- Thermodynamic properties of silicate glasses and melts: II. System SrO-SiO2
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High-temperature mass spectrometry was used to determine the Gibbs energies, activities, and chemical potentials of SrO and SiO2 in glasses and melts of the SrO-SiO2 system in the temperature range 1840-1970 K. Negative deviations fr
- Lopatin,Shugurov,Stolyarova,Tyurnina
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- Non-isothermal decomposition kinetics of alkaline earth metal carbonates
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The kinetics of thermal decomposition of four synthetic alkaline earth metal carbonates (MgCO3, CaCO3, SrCO3, and BaCO3) was studied under non-isothermal conditions using thermogravimetry. The activation energy and the pre-exponential factor for the decomposition reactions were determined using the Agarwal and Sivasubramanium integral approximation method. A new method was developed using a Turbo-C-based computer program to evaluate the integral of the kinetic equation. It was observed that the decomposition reaction of MgCO3 and CaCO 3 followed two-dimensional diffusion-controlled kinetics and the decomposition reaction of SrCO3 and BaCO3 followed a Ginstling-Brounshtein model-based diffusion-controlled kinetics.
- Maitra,Bandyopadhyay,Das,Pal,Pramanik
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- Oxidative Dimerisation of Methane over BaCO3, SrCO3 and these Catalysts promoted with Alkali
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The yield and selectivity for formation of C2 hydrocarbons from CH4 and O2 were 18.2 and 48.4 percent respectively over 2 g of BaCO3 at 1073 K at a CH4 : O2 ratio of 2.0 : 1, whereas the yield and selectivity were 2.5 and 99.5 percent over SrCO3 at 973 K at a CH4 : O2 ratio of 37.9 : 1.
- Aika, Ken-ichi,Moriyama, Takeshi,Takasaki, Nobuhiro,Iwamatsu, Eiji
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- EPR study of electron trapping on partially hydroxylated alkali-earth oxides occurring during SO2 disproportionation
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We used the Electron Paramagnetic Resonance (EPR) technique to study the interaction of SO2 molecules on bare and partially hydroxylated alkali-earth oxide (AEO) surface. When SO2 is adsorbed on the surfaces of higher basicity (CaO and SrO) disproportionation reaction occurs with the formation of SO2- radical. We show also that, when the same reaction is present on partially hydroxylated surfaces a fraction of the electrons exchanged during the redox process are trapped on the oxide surface forming colour centres ((H+)(e-) centres).
- Livraghi, Stefano,Paganini, Maria Cristina,Giamello, Elio
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- A novel mixed valent chromium-layered oxide with peculiar magnetic properties: Sr4.5Cr2.5O9
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A new mixed valent chromium-layered oxide, Sr4.5Cr2.5O9, with a structure closely related to the '0201-1201' structure of the superconducting cuprate TIBa(2-x)La(2+x)Cu2O9, has been synthesized at normal pressure. This orthorhombic phase (a = 10.7 59(2) A, b = 5.4012(1) A, and c = 30.0755(6) A) consists of the regular intergrowth of [Sr2CrO4]0201 blocks and [(Sr0.5Cr0.5)Sr2CrO5]1201 blocks. It differs from the thallium cuprate by the 1:1 ordering of Sr and Cr species within the intermediate layer of the '1201' block, so that at this level CrO4 tetrahedra, containing Cr6+ species, are obtained. Moreover, at the boundary between the '1201' and '0201' blocks, CrO6 octahedra alternate with CrO5 pyramids, both occupied by Cr3+ species. The magnetic measurements show an original metamagnetic transition from an antiferromagnetic to a weak ferromagnetic state. These properties are interpreted in terms of strong intralaye and weak interlayer magnetic couplings between Cr3+ species through a superexchange mechanism. (C) 2000 Academic Press.
- Pelloquin,Wahl,Masset,Maignan,Michel,Raveau
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- Crystal structures and magnetic properties of new europium melilites Eu2MSi2O7 (M = Mg, Mn) and their strontium analogues
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Synthesis, crystal structures, and magnetic properties of melilite-type oxides A2MSi2O7 (A = Sr, Eu; M = Mg, Mn) were investigated. These compounds crystallize in the melilite structure with space group P421m. The 151Eu Moessbauer measurements show that the Eu ions are in the divalent state. The Eu2MgSi 2O7 is paramagnetic down to 1.8 K. Long-range antiferromagnetic ordering is observed at 3.4 K for Sr2MnSi 2O7. On the other hand, the Eu2MnSi 2O7 shows a ferrimagnetic transition at 10.7 K. From the magnetization and specific heat measurements, it is found that the Eu 2+ (14 μB) and Mn2+ (5 μB) sublattices order antiferromagnetically. This result indicates that an interaction between f-d electrons (Eu-Mn) predominantly operate in this compound.
- Endo, Takashi,Doi, Yoshihiro,Wakeshima, Makoto,Hinatsu, Yukio
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- The magnetoelectric perovskite Sr3Fe2TeO9: An insight from magnetic measurements and neutron powder diffraction
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A study of the crystallographic and magnetic structures of the double perovskite Sr3Fe2TeO9 has been carried out on a polycrystalline sample using neutron powder diffraction (NPD) data between 10 and 650 K. An analysis of the NPD patterns at room temperature has shown that this compound crystallises in the tetragonal space group I4/m with a = 5.5614(7) ? and c = 7.867(1) ? and has a partially ordered arrangement of Fe and Te at the B-sites. The compound undergoes an I4/m → Fm-3m improper ferroelectric phase transition near 460 K. A low-temperature ferrimagnetic ordering (below TN = 260 K) has been followed from the magnetisation measurements and sequential NPD data analysis. In good agreement with magnetic measurements the ferrimagnetic structure with very weak magnetisation is defined by the propagation vector k = (0, 0, 0). In addition to the obtained experimental results on magnetic and electric properties some aspects of magnetoelectricity in this perovskite are also discussed and compared with those of another quaternary oxide Sr3Fe2B6+O9.
- Ivanov,Nordblad,Eriksson,Tellgren,Rundl?f
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- Reduction chemistry of platinum group metal perovskites
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The reduction chemistry of the perovskite and perovskite-related compounds, CaRuO3, SrRuO3, BaRuO3, SrIrO3, and BaIrO3, was examined. Samples were reduced at low temperatures (≤ 600°C) by direct reduction with hydrogen gas and by a method that utilized zirconium metal as an oxygen getter. No evidence for oxygen deficient perovskites was observed. In almost all cases, the mixed metal oxide was reduced to form the zero valent platinum group metal and the binary oxide or hydroxide (AO or A(OH)2). One exception was seen in the reduction of SrIrO3 via the getter method where the intermediate Sr4IrO6 was found.
- Wiley, John B.,Poeppelmeier, Kenneth R.
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- Kinetics of free-surface decomposition of magnesium, strontium and barium carbonates analyzed thermogravimetrically by the third-law method
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The results of our thermogravimetric experiments on the decompositions of MgCO3, SrCO3 and BaCO3 powders and some data reported in the literature were used for the determination of the E parameter of the Arrhenius equation by the third-law method and estimation of the self-cooling effect on the results of these determinations. The experimental values of the E parameters for these carbonates (218, 286 and 302 kJ mol -1) are much higher than the enthalpies of equilibrium reactions (up to solid oxide and CO2) and the values accepted by TA community as the reference data. At the same time, these data are in a good agreement with the mechanism of congruent dissociative evaporation of carbonates with the simultaneous condensation of low-volatility oxides. Differences in the magnitudes of the τ parameter responsible for the consumption of condensation energy by the reactant are revealed. Instead of expected 0.50, the magnitudes of the τ parameter for Mg, Sr and Ba carbonates are as follows: 0.47, 0.42 and 0.10.
- L'vov, Boris V.,Ugolkov, Valery L.
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- High-pressure synthesis and crystal structures of the strontium oxogallates Sr2Ga2O5 and Sr5Ga6O14
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Abstract High-pressure synthesis experiments in a piston-cylinder apparatus at 1.5 GPa/3.0 GPa and 1000°C resulted in the formation of single-crystals of Sr2Ga2O5 and Sr5Ga6O14, respectively. The structures of both compounds have been solved from single-crystal diffraction data sets using direct methods. The first compound is orthorhombic with space group type Pbca (a=10.0021(4) ?, b=9.601(4) ?, c=10.6700(4) ?, V=1024.6(4) ?3, Mr=394.68 u, Z=8, Dx=5.12 g/cm3) and belongs to the group of single layer gallates. Individual sheets are parallel to (0 0 1) and can be built from the condensation of unbranched vierer single chains running along [0 1 0]. The layers are characterized by the presence of four- and strongly elliptical eight-membered rings of corner connected tetrahedra in UUDD and UUUUDDDD conformation. Strontium atoms are sandwiched between the tetrahedral layers for charge compensation and are coordinated by six and seven oxygen ligands, respectively. Sr2Ga2O5 is isotypic with several other double sulfides and selenides. To the best of our knowledge, it is the first example of an oxide with this structure type. From a structural point of view, Sr5Ga6O14 is a phyllogallate as well. The crystal structure adopts the monoclinic space group P21/c (a=8.1426(3) ?, b=8.1803(3) ?, c=10.8755(4) ?, β=91.970(4)°V=723.98(5) ?3, Mr=1080.42 u, Z=2, Dx=4.96 g/cm3). Individual sheets extend along (0 0 1). Basic building units are unbranched dreier single chains parallel to [1 0 0]. The layers contain tertiary (Q3) und quaternary (Q4) connected [GaO4]-tetrahedra in the ratio 2:1 resulting in a Ga:O ratio of 3:7 and the formation of exclusively five-membered rings. Linkage between adjacent tetrahedral sheets is provided by three symmetrically independent strontium ions which are surrounded by six to eight oxygen atoms. The layers in Sr5Ga6O14 are similar to those observed in the melilite structure-type. Crystallochemical relationships between the present phases and other known compounds are discussed in detail.
- Kahlenberg, Volker,Goettgens, Valerie,Mair, Philipp,Schmidmair, Daniela
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- Synthesis and Crystal Chemistry of a New Manganite Member Bi3.6Sr12.4Mn8O28+δ,n=2 of the [Bi2Sr2MnO6]n[Sr8Mn 6O16+δ]-Related Tubular Family
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A manganite with a tubular structure derived from the 2201-type, Bi3.6Sr12.4Mn8O28+δ, has been synthesized. Its complex crystal chemistry has been studied using XRD, ND, and HREM techniques. It crystallizes in an orthorhombic cell, space groupPbnb, witha=5.4946 A,b=23.595(1) A, andc=23.580(1) A. This structure can be described as an intergrowth, along b, of two types of (010) slices: 2201 -type slices [Bi2Sr2MnO6] that are two octahedra thick and manganese-deficient perovskite-related slices [Sr8Mn6O16+δ] that are one octahedron thick. A similar stacking is observed along c, which endows the structure with a pseudotetragonal character. Another way to describe this structure is to consider criss-crossing layers of manganese polyhedra forming tubes, where the [BiO] rows are inserted, and oxygen-deficient pillars, built up of four Mn polyhedra. This phase represents then=2 member of a new tubular family [Bi2Sr2MnO6]n[Sr8Mn 6O16+δ]. Intergrowth and shearing mechanisms arise along the b and c directions, in agreement with the pseudotetragonal character of the structure. The investigation of the transport and magnetic properties of this new manganite shows that it is an insulator and exhibits weak antiferromagnetism at low temperature (θp=-650 K); the high-temperature data evidence an effective magnetic moment of 4.7μBcharacteristic of high-spin Mn3+(μth=4.9μB).
- Pelloquin,Michel,Maignan,Hervieu,Raveau
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- Role of SrMoO4 in Sr2MgMoO6 synthesis
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Here we investigate the elemental and phase compositions during the solid-state synthesis of the promising SOFC-anode material, Sr 2MgMoO6, and demonstrate that molybdenum does not notably evaporate under the normal synthesis conditions with temperatures up to 1200 °C due to the formation of SrMoO4 as an intermediate product at low temperatures, below 600 °C. However, partial decomposition of the Sr2MgMoO6 phase becomes evident at the higher temperatures (~1500 °C). The effect of SrMoO4 on the electrical conductivity of Sr2MgMoO6 is evaluated by preparing a series of Sr2MgMoO6 samples with different amounts of additional SrMoO4. Under the reducing operation conditions of an SOFC anode the insulating SrMoO4 phase is apparently reduced to the highly conductive SrMoO3 phase. Percolation takes place with 2030 wt% of SrMoO4 in a Sr2MgMoO6 matrix, with a notable increase in electrical conductivity after reduction. Conductivity values of 14, 60 and 160 S/cm are determined at 800 °C in 5% H2/Ar for the Sr2MgMoO6 samples with 30, 40 and 50 wt% of added SrMoO4, respectively.
- Vasala,Yamauchi,Karppinen
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- Synthesis and structure of cobalt (II) oxide halides - Sr2CoO2X2 (X=Cl, Br)
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The first layered cobalt (II) oxide halides, Sr2CoO2Cl2 and Sr2CoO2Br2, have been synthesized and their structures determined from Rietveld refinement of powder X-ray data. The materials are structural analogues of the K2NiF4 cuprate phase Sr2CuO2Cl2, crystallizing in space group I4/mmm. The compounds contain CoO2 square planes separated by SrX layers (X=Cl,Br). The bromide material displays the expected increase in cell dimensions, i.e., for Sr2CoO2Cl2, a = 4.06251(5) A, c = 15.1251(3) A and for Sr2CoO2Br2, a = 4.08891(7) A, c = 16.4077(4) A.
- Knee, Christopher S.,Weller, Mark T.
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- Synthesis, crystal structure, and magnetic properties of a novel layered manganese oxide Sr2MnGaO5+δ
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New Sr2MnGaO4.97 complex oxide was synthesized by solid state reaction in sealed silica tubes at 950-1000°C. The Sr2MnGaO4.97 crystal structure was refined from X-ray powder diffraction data. Sr2MnGaO4.97 is based on the Ima2 brownmillerite-type structure with apically elongated MnO6 octahedra due to a Jahn-Teller effect. Electron diffraction and high-resolution electron microscopy showed that local ordering of the left- and right-hand chains of GaO4 tetrahedra in Sr2MnGaO4.97 leads to a superstructure with a doubling of the b parameter of the orthorhombic unit cell. The formal oxidation state of Mn (VMn) can be varied by thermal treatments at elevated oxygen pressure (450°C, 20 bar of O2). The oxygen insertion induces a structure transformation in oxidized Sr2MnGaO5.47 material with the formation of a tetragonal perovskite-like structure (a ≈ ap, c ≈ 2cp) with oxygen vacancies located in the Ga layers. The oxidation is accompanied by a significant compression of the Mn-O apical distances and a suppression of the Jahn-Teller deformation. Both Sr2MnGaO4.97 and Sr2MnGaO5.47 can probably be treated as canted antiferromagnets with TN~150 and 80 K, respectively.
- Abakumov,Rozova,Pavlyuk,Lobanov,Antipov,Lebedev,Van Tendeloo,Ignatchik,Ovtchenkov,Koksharov,Vasil'ev
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- Synthesis of phthalide-skeleton using selective intramolecular Tishchenko reaction over solid base catalysts
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An efficient, economical, and environmentally benign method for the synthesis of phthalide-skeleton using heterogeneous catalytic intramolecular Tishchenko reaction with solid bases is described. Among the solid base catalysts examined, MgO, CaO, and SrO exhibited high catalytic performances for the intramolecular Tishchenko reaction of o-phthalaldehyde to yield phthalide exclusively in excellent yields at 313 K in the short time span of 0.25 h. Application of γ-alumina to the intramolecular Tishchenko reaction of o-phthalaldehyde was also successful; phthalide was obtained selectively in excellent yields at 313 K in 4 h. The employment of KF/alumina and KOH/alumina at 313 K for 4 h resulted in the selective formation of phthalide in moderate yields. The heterogeneous catalytic systems realized by the use of CaO and γ-alumina were also successfully applicable to the selective intramolecular Tishchenko reaction of 2,3-naphthalenedicarbaldehyde to give the corresponding five-membered lactone in excellent yields at 333 K for 2 and 20 h, respectively. Based on the reaction results, the infrared spectra of adsorbed o-phthalaldehyde, and the quantum chemical calculations conducted at the PM3-MO level of theory for elucidation of the molecular and electronic structures of o-phthalaldehyde and the potential intermediates, a plausible reaction mechanism for the intramolecular Tishchenko reaction of o-phthalaldehyde to phthalide over MgO and γ-alumina was proposed. The catalytically active species should be o-MOCH2C6H4CHO (M=Mg or Al).
- Seki, Tsunetake,Tachikawa, Hiroto,Yamada, Takashi,Hattori, Hideshi
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- Kinetics of dehydration and thermal decomposition of Sr(NO3)2 ·4H2O and its deuterated analogue with a view to obtaining SrO
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The kinetics and mechanism of the thermal-dehydration of Sr(NO3). 4H2O and its deuterated analogue were studied by means of the DTA, TG and DSC. The temperatures, enthalpies and weight losses of phase transitions were measured. The dehydration occurs in a stepwise manner, and the composition of the intermediate depends on the rate of thermal decomposition. The kinetic parameters (E* and Z) for the two steps of dehydration at a heating rate of 5 deg min-1 were calculated. A correlation was found between the disperity of the end-product of the thermal decomposition (SrO) and the conditions of its preparation.
- Maneva,Petroff
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- High-Spin cobalt(II) ions in square planar coordination: Structures and magnetism of the oxysulfides Sr2CoO2Cu2S 2 and Ba2CoO2Cu2S2 and their solid solution
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The antiferromagnetic structures of the layered oxychalcogenides (Sr 1-xBax)2CoO2Cu2S 2 (0 ≥ x ≥ 1) have been determined by powder neutron diffraction. In these compounds Co2+ is
- Smura, Catherine F.,Parker, Dinah R.,Zbiri, Mohamed,Johnson, Mark R.,Gal, Zoltan A.,Clarke, Simon J.
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- Kinetics and mechanism of free-surface decomposition of solid and melted AgNO3 and Cd(NO3)2 analyzed thermogravimetrically by the third-law method
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The third-law method and the retardation effect of the excess of gaseous product in the reactor were used for thermogravometric (TG) investigation of kinetics and mechanisms of thermal decomposition of AgNO3 and Cd(NO3)2. The most important results of this study are formulated as follows. (i) In contrast to AgNO3, the evolution of oxygen in the process of decomposition of Cd(NO3)2 proceeds in the form of free atoms (O). This explains, in particular, the absence of O2 molecules in primary products of Cd(NO 3)2 decomposition revealed earlier by quadrupole mass spectroscopy (QMS). (ii) The decomposition rate is reduced after reactant melting because of the absence of product/reactant interface and associated transfer of condensation energy to the reactant. This conclusion is supported by a rise of the E parameter of the Arrhenius equation by about 20 kJ mol -1 after melting of AgNO3 and Cd(NO3) 2. (iii) The absence of layer of solid product in case of decomposition of melt provides conditions for a free evaporation in vacuum of all primary products including the low-volatility species. This phenomenon was observed in experiments on decomposition of AgNO3 melt in vacuum.
- L'vov, Boris V.,Ugolkov, Valery L.
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- Suppression of magnetic order in Sr3Fe2O 4Cl2 by Fe-site substitution by cobalt
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The low-temperature topotactic reduction of Sr3Fe 2-xCoxO5Cl2 oxychloride phases with LiH allows the preparation of phases of composition Sr3Fe 2-xCoxO4Cl2 (0 ≥ x ≥ 1). The reduced phases adopt body-centered tetragonal structures which are isostructural with Sr3Fe2O4Cl2 and contain square-planar (Fe/Co)O4 centers connected into apex-linked sheets, analogous to the CuO2 sheets present in superconducting cuprate phases. As the cobalt concentration in Sr3Fe2-xCo xO4Cl2 is increased the antiferromagnetic order of the Sr3Fe2O4Cl2 host phase is suppressed, ultimately leading to spin-glass behavior, at low temperature, in Sr3Fe2-xCoxO4Cl2 phases with x ≥ 0.8. The limited influence of cobalt substitution on the reactions which form the Sr3Fe2-xCoxO4Cl 2 phases is discussed and contrasted to that of the related SrFeO3-δ-SrFeO2 system.
- Dixon, Edward,Hayward, Michael A.
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- Coupled anion and cation ordering in Sr3RFe4O 10.5 (R=Y, Ho, Dy) anion-deficientperovskites
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The Sr3RFe4O10.5 (R=Y, Ho, Dy) anion-deficient perovskites were prepared using a solid-state reaction in evacuated sealed silica tubes. Transmission electron microscopy and 57Fe Mssbauer spectroscopy evidenced a complete A-cations and oxygen vacancies ordering. The structure model was further refined by ab initio structure relaxation, based on density functional theory calculations. The compounds crystallize in a tetragonal a≈2√2ap≈11.3 A, ≈4p≈16A unit cell (ap: parameter of the perovskite subcell) with the P42/mnm space group. Oxygen vacancies reside in the (FeO5/4□3/4) layers, comprising corner-sharing FeO4 tetrahedra and FeO5 tetragonal pyramids, which are sandwiched between the layers of the FeO 6 octahedra. Smaller R atoms occupy the 9-fold coordinated position, whereas the 10-fold coordinated positions are occupied by larger Sr atoms. The Fe sublattice is ordered aniferromagnetically up to at least 500 K, while the rare-earth sublattice remains disordered down to 2 K.
- Abakumov, Artem M.,D'Hondt, Hans,Rossell, Marta D.,Tsirlin, Alexander A.,Gutnikova, Olga,Filimonov, Dmitry S.,Schnelle, Walter,Rosner, Helge,Hadermann, Joke,Van Tendeloo, Gustaaf,Antipov, Evgeny V.
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- A new 2212-type stair like structure: Bi14Sr21Fe 12O61, m=5 member of the generic [Bi2Sr 3Fe2O9]m[Bi4Sr 6Fe2O16] family
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A new oxide, Bi14Sr21Fe12O61, with a layered structure derived from the 2212 modulated type structure Bi 2Sr3Fe2O9, was isolated. It crystallizes in the I2 space group, with the following parameters: a=16.58(3)A, b=5.496(1)A, c=35.27(2)A and β=90.62°. The single crystal X-ray structure determination, coupled with electron microscopy, shows that this ferrite is the m=5 member of the [Bi 2Sr3Fe2O9]m[Bi 4Sr6Fe2O16] collapsed family. This new collapsed structure can be described as slices of 2212 structure of five bismuth polyhedra thick along a→, shifted with respect to each other and interconnected by means of [Bi4Sr6Fe2O 16] slices. The latter are the place of numerous defects like iron or strontium for bismuth substitution; they can be correlated to intergrowth defects with other members of the family.
- Allix,Perez,Pelloquin,Hervieu,Raveau
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- Model study on transesterification of soybean oil to biodiesel with methanol using solid base catalyst
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Modeling of the transesterification of vegetable oils to biodiesel using a solid base as a catalyst is very important because the mutual solubilities of oil and methanol will increase with the increasing biodiesel yield. The heterogeneous liquid-liquid-solid reaction system would become a liquid-solid system when the biodiesel reaches a certain content. In this work, we adopted a two-film theory and a steady state approximation assumption, then established a heterogeneous liquid-liquid-solid model in the first stage. After the diffusion coefficients on the liquid-liquid interface and the liquid-solid interface were calculated on the basis of the properties of the system, the theoretical value of biodiesel productivity changing with time was obtained. The predicted values were very near the experimental data, which indicated that the proposed models were suitable for the transesterification of soybean oil to biodiesel when solid bases were used as catalysts. Meanwhile, the model indicated that the transesterification reaction was controlled by both mass transfer and reaction. The total resistance will decrease with the increase in biodiesel yield in the liquid-liquid-solid stage. The solid base catalyst exhibited an activation energy range of 9-20 kcal/mol, which was consistent with the reported activation energy range of homogeneous catalysts.
- Liu, Xuejun,Piao, Xianglan,Wang, Yujuri,Zhu, Shenlin
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- Preparation, crystal structure, and magnetic studies of a new Sr7Re4O19double oxide and its relation to the structure of Ba7Ir6O19
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The complex oxide Sr7Re4O19has been synthesized and its crystal structure was determined by X-ray diffraction powder data analysis (space group C2/m; a=13.6379(3) A, b=5.6035(2) A, c=10.3700(3) A; β=98.348(2)°, Z=2, RI=0.018, Rp=0.050). The compound crystallizes in a new structure type, which can be derived from the Ba7Ir6O19 structure by removing the Ir atoms from the middle octahedron of three face-sharing IrO6octahedra units. This change results in the infinite cis-bridged chains of the ReO6 octahedra linked together by common corners. Each chain is connected with another one by the corner-sharing of each second ReO6octahedron. The 10- and 12-coordinated Sr atoms are situated between these infinite structure fragments. Magnetic properties of the Sr7Re4O19 compound were studied by SQUID measurements.
- Bramnik,Ehrenberg,Fuess
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- Long-range ordering in the Bi1-xAexFeO 3-x/2 perovskites: Bi1/3Sr2/3FeO2.67 and Bi1/2Ca1/2FeO2.75
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Two-ordered perovskites, Bi1/3Sr2/3FeO2.67 and Bi1/2Ca1/2FeO2.75, have been stabilized and characterized by transmission electron microscopy, Moessbauer spectroscopy and X-ray powder diffraction techniques. They both exhibit orthorhombic superstructures, one with a ≈ b ≈ 2ap and c ≈ 3ap (S.G.: Pb2n or Pbmn) for the Sr-based compound and one with a ≈ b ≈ 2ap and c ≈ 8ap (S.G.: B222, Bmm2, B2mm or Bmmm) for the Ca-based one. The high-resolution transmission electron microscopy (HRTEM) images evidence the existence of one deficient [FeOx]∞ layer, suggesting that Bi1/3Sr2/3FeO2.67 and Bi 1/2Ca1/2FeO2.75 behave differently compared to their Ln-based homolog. The HAADF-STEM images allow to propose a model of cation ordering on the A sites of the perovskite. The Moessbauer analyses confirm the trivalent state of iron and its complex environment with three types of coordination. Both compounds exhibit a high value of resistivity and the inverse molar susceptibility versus temperature curves evidence a magne tic transition at about 730 K for the Bi1/3Sr2/3FeO2.67 and a smooth reversible transition between 590 and 650 K for Bi1/2Ca1/2FeO2.75.
- Lepoittevin,Malo,Barrier,Nguyen,Van Tendeloo,Hervieu
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- Mixed Tishchenko reaction over solid base catalysts
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Catalytic behaviors of solid base catalysts for mixed Tishchenko reactions were investigated to elucidate the activity- and selectivity-determining factors in active sites of the catalysts and molecular structures of the reactants. A mixture containing equal amounts of two kinds of aldehydes was allowed to react at 353 K. The aldehydes used were benzaldehyde, pivalaldehyde, and cyclopropanecar-baldehyde. For all the reactions, the catalytic activity of alkaline earth oxides increased in the order of BaO ? MgO 2O3, ZrO2, ZnO, γ-alumina, hydrotalcite, KF/alumina, and KOH/alumina, were all inactive for the mixed Tishchenko reaction of benzaldehyde and pivalaldehyde; not only crossed-condensation products but also self-condensation products hardly formed. Quantum chemical calculations of the positive charges on the carbonyl carbon atoms of aldehydes and the structure parameters of the active species for the ester formations account for the observed selectivities to four Tishchenko dimers. The selectivities to four Tishchenko dimers over MgO and CaO are determined primarily in the step of the nucleophilic addition of the active species (PhCH2O-, tBuCH2O-, and C3H5CH2O-) to the carbonyl carbon atoms of aldehydes. The reaction of the aldehyde having a more positively charged and sterically less-hindered carbonyl carbon atom with the active species having a less-hindered oxygen atom proceeds faster.
- Seki, Tsunetake,Kabashima, Hajime,Akutsu, Kazumasa,Tachikawa, Hiroto,Hattori, Hideshi
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- Oxygen non-stoichiometry in the (Tl,Pb)-Sr-Ca-Cu-O 1212 system
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Materials in the (Tl, Pb)Sr2CaCu2O7-δ system have been synthesized with different oxygen stoichiometries and their structure and superconducting properties studied. Powder neutron-diffraction studies reveal that for δ>0 va
- Ogborne, D. M.,Weller, M. T.
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- Extension of the 1201 family to strontium-rich chromite and ferrite, Bi0.4Sr2.5Cr1.1O4.9 and Bi0.4Sr2.5Fe1.1O5
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Two new Sr-rich 1201 -type oxides, Bi0.4Sr2.5Cr1.1O4.9 and Bi0.4Sr2.5Fe1.1O5 have been synthesized. These compounds, intergrowths of double rock-salt layers with single perovskite layers, show a 1:1 ordering between (Bi,M) and Sr species within the intermediate rock-salt layer [Bi0.4M0.1Sr0.5O]. The XANES study shows that bismuth is mainly trivalent, whereas iron is mixed valent containing 50% Fe3+ and 50% Fe4+ (also confirmed by Moessbauer), and chromium could be a mixture of Cr3+ and Cr6+ sitting inthe perovskite and rock-salt-type sites, respectively. Both compounds exhibit antiferromagnetic interactions. The Cr-phase is a strong insulator, whereas the Fe-phase exhibits a semi-conductor-like resistivity whose value at room temperature is close to that of isotypic cobaltite.
- Allix,Pelloquin,Studer,Nguyen,Wahl,Maignan,Raveau
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- Topochemical fluorination of Sr3(M0.5Ru 0.5)2O7 (M = Ti, Mn, Fe), n = 2, Ruddlesden-popper phases
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Reaction of the appropriate Sr3(M0.5Ru 0.5)2O7 (M = Ti, Mn, Fe), n = 2, Ruddlesden-Popper oxide with CuF2 under flowing oxygen results in formation of the oxide-fluoride phases Sr3(Ti0.5Ru 0.5)2O7F2, Sr3(Mn 0.5Ru0.5)2O7F2, and Sr3(Fe0.5Ru0.5)2O 5.5F3.5 via a topochemical anion insertion/substitution process. Analysis indicates the titanium and manganese phases have Ti 4+, Ru6+ and Mn4+, Ru6+ oxidation state combinations, respectively, while Moessbauer spectra indicate an Fe3+, Ru5.5+ combination for the iron phase. Thus, it can be seen that the soft fluorination conditions employed lead to formation of highly oxidized Ru6+ centers in all three oxide-fluoride phases, while oxidation states of the other transition metal M cations remain unchanged. Fluorination of Sr3(Ti0.5Ru0.5) 2O7 to Sr3(Ti0.5Ru 0.5)2O7F2 leads to suppression of magnetic order as the fluorinated material approaches metallic behavior. In contrast, fluorination of Sr3(Mn0.5Ru0.5) 2O7 and Sr3(Fe0.5Ru 0.5)2O7 lifts the magnetic frustration present in the oxide phases, resulting in observation of long-range antiferromagnetic order at low temperature in Sr3(Mn0.5Ru 0.5)2O7F2 and Sr3(Fe 0.5Ru0.5)2O5.5F3.5. The influence of the topochemical fluorination on the magnetic behavior of the Sr3(M0.5Ru0.5)2OxF y phases is discussed on the basis of changes to the ruthenium oxidation state and structural distortions.
- Romero, Fabio Denis,Bingham, Paul A.,Forder, Susan D.,Hayward, Michael A.
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- Synthesis and thermal study of 8-hydroxy-quinoline derivatives of the alkaline Earth metals: I. Strontium complexes
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Strontium complexes of 5,7-dibromo-, 5,7-dichloro-, 7-iodo- and 5-chloro-7-iodo-8-hydroxyquinoline were precipitated from an aqueous ammonia and acetone medium. The complexes obtained were Sr[(C9H4ONBr2)2]·2.5H 2O; Sr[(C9H4ONCl2)(OH)]·1.5H2O; Sr[(C9H5ONI)2]·5H2O and Sr[(C9H4ONICl)(OH)]·1.25H2O. The residues of their thermal decomposition were SrBr2; a mixture of SrCl2, SrCO3 and SrO3 SrCO3, and SrCO3, respectively. All were characterized by means of thermogravimetry, differential thermal analysis, complexometry with EDTA, atomic absorption spectroscopy, IR spectroscopy and X-ray diffraction.
- Guerreiro,Ribeiro,Crespi,Torres
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- Structure-property relationships in a series of mixed layer pnictide oxide compounds: A2Mn3Pn2O2 (A = Sr, Ba; Pn = P, As, Sb)
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Results of magnetic property measurements for the compounds A2Mn3Pn2O2 (A = Sr, Ba; Pn = P, As, Sb) are reported and discussed in the light of structural trends in the series. The structure consists of a 1:1 intergrowth of metal oxide layers in which the metal coordination is square planar and metal pnictide layers in which the coordination is tetrahedral. With the exception of Sr2Mn3As2O2, magnetic susceptibility data reveal the presence of broad maxima that have been assigned to coupling of the MnO2-2 layers. The data have been fitted assuming a 2D Heisenberg antiferromagnet model and the intraplanar coupling constants obtained are observed to increase as the a parameter or metal oxygen bond length decreases. The same trend is observed for the relationship of transition temperatures, obtained from dχT/dT plots, to the a axial parameters. The exception to the rule is Sr2Mn3As2O2, which has an anomalously low transition temperature and different magnetic behavior for field-cooled versus zero-field-cooled samples. The field-cooled data show a sharp antiferromagnetic transition whereas the zero-field-cooled data show no transition to 3D order between 5 and 300 K.
- Brock, Stephanie L.,Kauzlarich, Susan M.
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- Variation of physical properties in the nominal Sr4V 2O6Fe2As2
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We show using a combination of powder X-ray and neutron diffraction, first-principles calculations, temperature- and field-dependent magnetization, heat capacity and resistivity data that the superconducting behavior of 'Sr 4V2O6Fe2As2' is dependent on synthesis conditions, particularly, heating profiles result in unintentional chemical doping. This compound can be tuned from a state in which the vanadium electrons are itinerant with a high electronic density of states, to a state where the vanadium-oxide layers are insulating and presumably magnetic.
- Sefat, Athena S.,Singh, David J.,Ovidiu Garlea,Zuev, Yuri L.,McGuire, Michael A.,Sales, Brian C.
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- Efficient heterogeneous catalytic intramolecular Tishchenko reaction of o-phthalaldehyde to phthalide with alkaline earth oxides
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The heterogeneous catalytic systems realized by alkaline earth oxides are successfully applicable to the highly efficient intramolecular Tishchenko lactonization of o-phthalaldehyde to phthalide.
- Seki,Hattori
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- Application of non-arrhenius method for analyzing the decomposition kinetics of SrCO3 and BaCO3
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The nonisothermal kinetics of thermal decomposition of SrCO3 and BaCO3 was studied by thermo-gravimetry following non-Arrhenius integral approach of Harcourt and Esson. Variation of activation energy of these two carbonates with frac
- Maitra, Saikat,Bandyopadhyay, Narayan,Pal, Jayita
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- Characterization of an alkaline earth metal-doped solid superacid and its activity for the esterification of oleic acid with methanol
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The leaching of grafted sulfate groups is one of the major issues for the solid acid catalysts with sulfate modification. A detailed study of sulfated alkaline earth metal-ferric composite oxides was carried out to suppress the leaching of sulfate groups as well as maintain high reactivity during the esterification of oleic acid. The acid properties and quantities of the active sites present on the catalysts were studied with pyridine-adsorption, FT-IR, TGA, and titration methods. The following order of acidic strength was observed: SO42-/Sr-Fe oxide > SO42-/Ca-Fe oxide > SO42-/Mg-Fe oxide. After sulfate modification, sulfate ions are linked to the composite oxides in a bridged bidentate form. SO42-/Sr-Fe oxide exhibits superacidic nature due to the high induction effect of the sulfated ion grafted on the Sr cation. TGA and FT-IR spectroscopic analyses provide new insights into the function of the iron cations implanted on the catalyst surface for enhancing the turnover frequency (TOF) of the active sites on SO42-/Sr-Fe oxide in the esterification. It was verified that the active energy of SO42-/Sr-Fe oxide for the esterification of oleic acid with methanol was as low as 28.53 ± 0.72 kJ mol-1. In the reusability study, SO42-/Sr-Fe oxide exhibited high reusability in the esterification, due to the high stability of the sulfate ion grafted on SO42-/Sr-Fe oxide.
- Huang, Chien-Chang,Yang, Chieh-Ju,Gao, Pei-Jyuan,Wang, Nai-Ci,Chen, Ching-Lung,Chang, Jo-Shu
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- Synthesis, physical and photo electrochemical characterization of La-doped SrSnO3
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The transport properties of Sr0.98La0.02SnO3-δ in the system Sr1-xLaxSnO3-δ, after which the pyrochlore La2Sn2O7 appears, were investigated over the temperature range 4.2-300 K. The oxide was found to be n-type semiconductor with concomitant reduction of Sn4+ into Sn2+. The magnetic susceptibility was measured down to 4.2 K and is less than 3×10-5 emu cgs mol-1 consistent with itinerant electron behavior. The electron is believed to travel in a narrow band of Sn:5s character with an effective mass ~4 mo. The highest band gap is 4.32 eV and the optical transition is directly allowed. A further indirect transition occurs at 4.04 eV. The electrical conductivity follows an Arrhenius-type law with a thermal activation of 40 meV and occurs by small polaron hopping between nominal states Sn4+/2+. The linear increase of thermo-power with temperature yields an electron mobility μ300 K (2×10-4 cm2 V-1 s-1) thermally activated. The insulating-metal transition seems to be of Anderson type resulting from random positions of lanthanum sites and oxygen vacancies. At low temperatures, the conduction mechanism changes to a variable range hopping with a linear plot Ln ρ-1 vs. T-4. The photo electrochemical (PEC) measurements confirm the n-type conductivity and give an onset potential of -0.46 VSCE in KOH (1 M). The Mott-Schottky plot C-2-V shows a linear behavior from which the flat band potential Vfb=+0.01 VSCE at pH 7 and the doping density ND=1.04×1021 cm-3 were determined.
- Hadjarab,Bouguelia,Trari
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- Synthesis and crystal structure of oxygen-deficient Bilayer Ruthenate Sr3Ru2O7-δ
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The structural properties of oxygen-deficient Ruddlesden-Popper-type Sr3Ru2O7-δ compounds are presented. Sr3Ru2O7-δ compounds (δ≤0.17, 0.23, 0.28, 0.40, and 0.47) were obtained by hydrogen reduction of the parent Sr3Ru2O7 ruthenate. Rietveld structure refinements were performed to determine the crystal structure of the reduced compounds. Oxygen deficiency in the samples was studied by redox titrations and the Ru3+ content was confirmed by electron paramagnetic resonance. Magnetisation measurements were performed to study the magnetic response of the reduced phases. Removal of the oxygen atoms from the parent compound resulted in the decrease of the c-lattice parameter and increase of the a-lattice parameter that is related to partial reduction of Ru4+, in Sr3Ru2O7, to Ru3+. Rietveld analyses showed that the apical oxygen atoms of the RuO6 octahedra were partially lost during reduction. Redox titration experiments showed a linear correlation between reduction of the compounds and the annealing time under H2. CSIRO 2014.
- Martinez-Anaya, Oliver,Garcia-Valdes, Jesus,De La Mora, Pablo,Tavizon, Gustavo
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- Constitution of the Sr-Ni-O system
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The constitution of the Sr-Ni-O system was studied experimentally for the first time. Samples were prepared either from SrCO3 and NiO or from Sr(NO3)2 and Ni(NO3)2·6H 2O and characterized by high-temperature X-ray powder diffraction, scanning electron microscopy, thermogravimetric and differential thermal analyses. In the SrO-NiO quasibinary system an eutectic reaction: liquid?SrO+NiO was found to occur at 1396±5°C, while the homogeneity range of terminal solid solutions is negligible. Thermodynamic calculations using the regular solution model for the liquid and rocksalt-type phases were employed to predict liquidus and solidus curves. Three ternary compounds, SrNiO2.5, Sr5Ni4O11, and Sr9Ni7O21 were observed in the samples prepared from nitrate solutions, but only Sr9Ni7O21 was proved to be thermodynamically stable in air up to 1030±6°C. When heating in air, SrNiO2.5 and Sr5Ni4O 11 were found to transform irreversibly into a mixture of Sr 9Ni7O21 and NiO. Isothermal section of the SrO-NiO-O subsystem, which represents phase equilibria at 950-1030°C as well as an isobaric section of the Sr-Ni-O system in air were constructed.
- Zinkevich
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- The ability of RP-type cobaltites to accommodate carbonate groups: A new layered oxide Sr4Co2(CO3)O5.86
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The possibility to introduce carbonate groups inside a pure cobalt based Ruddlesden Popper type matrix is demonstrated. This paper reports the synthesis as a single phase of a new layered oxycarbonate Sr4Co 2(CO3)O5.8
- Demont,Pelloquin,Hebert,Breard,Hoewing,Miyazaki,Maignan
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- The standard enthalpies of formation of hydroxides, I. The alkaline-earth hydroxides β-Ba(OH)2 and Sr(OH)2
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The enthalpies of solution of β-Ba(OH)2(s) and Sr(OH)2(s) in 1.0109 mol*dm-3 HCl(aq) have been measured.From the results the standard molar enthalpies of formation have been calculated: ΔfH0mβ-Ba(OH)2, s, 298.1
- Konings, R. J. M.,Cordfunke, E. H. P.,Ouweltjes, W.
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- Topotactic oxidative and reductive control of the structures and properties of layered manganese oxychalcogenides
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Topotactic modification, by both oxidation and reduction, of the composition, structures, and magnetic properties of the layered oxychalcogenides Sr4Mn3O7.5Cu2Ch2 (Ch = S, Se) is described. These Mns
- Hyett, Geoffrey,Barrier, Nicolas,Clarke, Simon J.,Hadermann, Joke
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- Peculiarities of CaCO3, SrCO3 and BaCO3 decomposition in CO2 as a proof of their primary dissociative evaporation
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The results of thermogravimetric experiments on the decompositions of CaCO3, SrCO3 and BaCO3 in the presence of CO2 and some data reported in the literature were used for the determination of the E parameter of the Arrhenius equation by the third-law method. The values obtained (495, 569 and 605kJmol-1) are twice as much compared with the values of the E parameter obtained for these carbonates earlier in the absence of CO2. This fact together with the invariance of the E parameter with partial pressure of CO2 (P CO2) and a hyperbolic dependence of the rate of decomposition on PCO2 is in excellent agreement with the theoretical predictions deduced from the mechanism of decomposition that includes the primary stage of dissociative evaporation of reactant.
- L'vov, Boris V.,Ugolkov, Valery L.
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- Oxygen-ion and electron conductivity in Sr2(Fe1-xGax)2 O5
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High-temperature electrical conductivity measurements, structural data from powder X-ray diffraction and 57Fe Moessbauer spectroscopy were combined to study the interrelationship of oxygen ion transport and p- and n-type transport in Sr2(Fe1-xGax)2O 5, where x = 0, 0.1 and 0.2. Although gallium substitution generally decreases the total ion-electron transport, the transition of the orthorhombic brownmillerite structure to a cubic phase on heating results in the recurrence of the conductivity to the same high level as in the parent ferrite (x = 0). The changes of the partial contributions to the total conductivity as a function of x are shown to reflect a complicated interplay of the disordering processes that develop in the oxygen sublattice on heating in response to replacement of iron with gallium.
- Leonidov,Patrakeev,Bahteeva,Poholok,Filimonov,Poeppelmeier,Kozhevnikov
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- Comparative study of oxygen double exchange between O2 adsorbate and alkaline-earth oxides
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Thermal desorption of doubly exchanged oxygen molecules at temperatures above 800 K is observed not from MgO but from CaO and SrO powders after 18O2-gas exposure at room temperature. The exchange reaction was investigated using ab initio molecular-orbital calculations. The defective (111) surface clusters of CaO and SrO were found to prepare anion-charged reactive centers to accept the O2 adsorbate. The adsorbate was incorporated into a key O5-charged intermediate which can provide an oxygen molecule composed of two lattice atoms for desorptipn. The nonreactive character of the MgO surface in the ground state is ascribed to the presence of oxygen ions bound strongly at the lattice points.
- Huzimura, Ryoitiro,Matsumura, Keiko,Yamabe, Shinichi,Yanagisawa, Yasunori
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- Electron-donor Sites of Oxides as Investigated on Oxygen-17 Exchanged CaO Surfaces
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The electron-donor sites of various oxides (BaO, SrO, CaO, MgO, γ-Al2O3 and SiO2-Al2O3), activated under vacuum in the temperature range 1000 - 1273 K, have been investigated by adsorption of 9,10-dimethylanthracene (DMAN), chlorine and oxygen (90 percent 17O-enriched or non-enriched).Upon adsorption of DMAN, radical anions are formed on CaO, whereas radical cations are formed on SiO2-Al2O3.On oxides of intermediate base strength (MgO and γ-Al2O3) very low radical concentration was obtained.The data allow for a further specification of the correlation between electron acceptor-donor properties of oxides and their acid-base strength.Upon adsorption of Cl2, a two g-value e. s. r. signal (g1 = 2.002, g2 = 2.013) was observed on alkaline-earth oxides.A nearly identical signal was also observed on adsorption of O2 on the same oxides.Upon adsorption of O2 (non-enriched) on CaO samples, previously exchanged with 17O2, the above signal showed some relevant modifications, suggesting that the paramagnetic species contains oxygen atoms.The signal is tentatively assigned to a O33- surface species.This species is thought to be formed on the surface of alkaline-earth oxides in the electron-donation process from low-coordination oxidic sites (OCUS2-) toward acceptor molecules.The OCUS2- sites are therefore identified as the electron-donor sites.The work also includes a volumetric study of O2 adsorption on the various oxides.By comparing volumetric adsorption data with the concentration of radicals (O2- and O3-), it is possible to provide a description of the O2 adsorption mechanism on alkaline-earth oxides.
- Indovina, Valerio,Cordischi, Dante
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- Deciphering local complex order by HAADF in a disordered mixed polyanion iron oxide: Sr4Fe2[Fe0.5(SO4)0.25(CO3)0.25]O7.25
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A layered iron compound involving two divalent polyanions (carbonate and sulfate anions) was synthesized by solid state chemistry in a closed ampule in the form of a ceramic. The Sr4Fe2[Fe0.5(SO4)0.25(CO3)0.25]O7.25 compound derives from the third term of the Ruddlesden and Popper family, Sr4Fe3O10. A multiscale approach through transmission electron microscopy (TEM) and powder neutron diffraction (PND) studies shows that SO4 and CO3 groups substitute for the iron polyhedron of the central layer of the perovskite blocks and the absence of long range ordering between sulfate and carbonates and FeO5 groups. Nevertheless, waves disturbing the expected periodicity of the atomic layer are evidenced in HAADF images. An accurate analysis of these images provides a view of the local cationic order correlated with SO4 and CO3 for FeO5 substitution.
- Gonano, Bruno,Bréard, Yohann,Pelloquin, Denis,Caignaert, Vincent,Pérez, Olivier,Pautrat, Alain,Bazin, Philippe,Suard, Emmanuelle,Boullay, Philippe
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- The topotactic reduction of Sr3Fe2O 5Cl2-square planar Fe(II) in an extended oxyhalide
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The topotactic reduction of the oxychloride Sr3Fe 2O5Cl2 with LiH results in the formation of Sr3Fe2O4Cl2. Neutron powder diffraction data show that Sr3Fe2O4Cl 2 adopts a body-centered tetragonal crystal structure (I4/mmm, a = 4.008(1) A, c = 22.653(1) A at 388 K) with anion vacancies located within the SrO layer of the phase. This leads to a structure consisting of infinite sheets of corner-sharing Fe(II)O4 square planes. Variable-temperature neutron diffraction data show that Sr3Fe 2O4Cl2 adopts G-type antiferromagnetic order below TN ~ 378(10) K with an ordered moment of 2.81(9) μB per iron center at 5 K consistent with the presence of high-spin Fe(II). The observed structural and chemical selectivity of the reduction reaction is discussed. The contrast between the structure of Sr 3Fe2O4Cl2 and the isoelectronic all-oxide analogue (Sr3Fe2O5) suggests that by careful selection of substrate phases, the topotactic reduction of complex transition metal oxychlorides can lead to the preparation of novel anion-deficient phases with unique transition metal-oxygen sublattices which cannot be prepared via the reduction of all-oxide substrates.
- Dixon, Edward,Hayward, Michael A.
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- Structural and Thermodynamic Characterization of the Perovskite-Related Ba1+yUO3+xand (Ba, Sr)1+yUO3+xPhases
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The perovskite-type BaUO3structure has been investigated by X-ray and neutron diffraction. The Ba/U ratio, the (Ba, Sr)/U ratio, and the oxygen stoichiometry in Ba1+yUO3+xwere varied, and the integral enthalpies of formation were determined by solution calorimetry. In addition, equilibrium oxygen partial pressures were measured using a reversible EMF cell. The chemical defect mechanism is discussed, and it is shown that the continuous series BaUO3-Ba1+yUO3+x-Ba3UO 6exists in which uranium vacancies are gradually filled with barium ions whereas uranium is oxidized via the pentavalent to the hexavalent state in Ba3UO6(=Ba2(Ba,U)O6).
- Cordfunke,Booij,Smit-Groen,Van Vlaanderen,Ijdo
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- Crystal and Electronic Structures of A2NaIO6Periodate Double Perovskites (A = Sr, Ca, Ba): Candidate Wasteforms for I-129 Immobilization
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The synthesis, structure, and thermal stability of the periodate double perovskites A2NaIO6 (A= Ba, Sr, Ca) were investigated in the context of potential application for the immobilization of radioiodine. A combination of X-ray diffraction and neutron diffraction, Raman spectroscopy, and DFT simulations were applied to determine accurate crystal structures of these compounds and understand their relative stability. The compounds were found to exhibit rock-salt ordering of Na and I on the perovskite B-site; Ba2NaIO6 was found to adopt the Fm-3m aristotype structure, whereas Sr2NaIO6 and Ca2NaIO6 adopt the P21/n hettotype structure, characterized by cooperative octahedral tilting. DFT simulations determined the Fm-3m and P21/n structures of Ba2NaIO6 to be energetically degenerate at room temperature, whereas diffraction and spectroscopy data evidence only the presence of the Fm-3m phase at room temperature, which may imply an incipient phase transition for this compound. The periodate double perovskites were found to exhibit remarkable thermal stability, with Ba2NaIO6 only decomposing above 1050 °C in air, which is apparently the highest recorded decomposition temperature so far recorded for any iodine bearing compound. As such, these compounds offer some potential for application in the immobilization of iodine-129, from nuclear fuel reprocessing, with an iodine incorporation rate of 25-40 wt%. The synthesis of these compounds, elaborated here, is also compatible with both current conventional and future advanced processes for iodine recovery from the dissolver off-gas.
- Dixon Wilkins, Malin C.,George, Jonathan,Hyatt, Neil C.,Kim, Eunja,Kirk, Cameron,Knight, Kevin S.,Montoya, Eduardo,O'Sullivan, Sarah E.,Sun, Shi-Kuan,Weck, Philippe F.
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p. 18407 - 18419
(2020/12/23)
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- One-pot synthesis of glycidol from glycerol and dimethyl carbonate over a highly efficient and easily available solid catalyst NaAlO2
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The one-pot synthesis of glycidol from glycerol and dimethyl carbonate (DMC) was developed by using a solid base catalyst. A series of solid base catalysts have been investigated in this reaction. It was found that NaAlO 2, a cheap and easily available raw material, was a highly efficient heterogeneous catalyst for the one-pot synthesis of glycidol, and it can be easily recovered and reused. Under the reaction conditions of a DMC-glycerol molar ratio of 2, catalyst-glycerol weight ratio of 3%, reaction time of 90 min, and temperature of 80-92 °C, the conversion of glycerol and the selectivity to glycidol reached 94.7% and 80.7%, respectively. Activity tests of the catalyst after exposure to the air showed that, to a certain extent, the NaAlO2 catalyst is tolerant to water and carbon dioxide, which makes the present system a practically interesting process for glycidol synthesis.
- Bai, Rongxian,Zhang, Hongkun,Mei, Fuming,Wang, Shu,Li, Tao,Gu, Yanlong,Li, Guangxing
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p. 2929 - 2934
(2013/10/08)
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- METHOD OF MAKING ALCOHOLS
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A method of making one or more alcohols with a single hydroxy group, such as methanol and ethanol, the method comprising contacting a polyol and water with a basic catalyst. The polyol may be glycerol, for example. The '. catalyst may be magnesium oxide.
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Page/Page column 9
(2013/03/26)
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- Volatile Imidazoles and Group 2 Imidazole Based Metal Precursors
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Sterically hindered imidazole ligands are described, along with their synthesis, which are capable of coordinating to Group 2 metals, such as: calcium, magnesium, strontium, in an eta-5 coordination mode which permits the formation of monomeric or dimeric
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Page/Page column 29
(2012/02/15)
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- Synthesis and structural characterization of new phases in the cubic M 3Te2O6X2 (M = Sr, Ba; X = Cl, Br) structure family
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Four alkaline earth oxotellurate(IV) halides with common formula M 3Te2O6X2 (M = Sr, Ba; X = Cl, Br) have been prepared as polycrystalline powders and/or in the form of single crystals. All compounds crystallize in the cubic space group Fd (3) m with cell parameters a = 15.9351(4) A for Sr3Te2O 6Cl2 (single-crystal X-ray data), 16.052(5) A for Sr3Te2O6Br2 (powder X-ray data), 16.688(2) A for Ba3Te2O6Cl2 (single-crystal X-ray data) and 16.8072(3) A for Ba3Te 2O6Br1.64Cl0.36 (single-crystal X-ray data). The results of the crystal structure analyses reveal a rigid (3)[M3Te2O6]2+ framework which can be described as being composed of regular octahedra of two types of chemically non-bonded M6 octahedra that are capped by trigonal pyramidal [TeO3] anions located above every second face of one of the M 6 octahedra. The halide X- anions are situated in the voids of the [M3Te2O6]2+ framework. Dependent on the nature of the halogen, the anions show various kinds of occupational disorder which eventually led to a revision of the previous structure model of Ba3Te2O6Cl2. A comparative discussion with other structures of general formula M 3Ch2O6X2 (M = divalent metal; Ch = Te, Se; X = Cl, Br) is presented. Copyright
- Stoeger, Berthold,Weil, Matthias,Silich, Konstantin A.,Olenev, Andrey V.,Berdonosov, Peter S.,Dolgikh, Valery A.
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p. 1322 - 1329
(2011/11/05)
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- Thermoanalytical investigation of relative reactivity of some nitrate oxidants in tin-fueled pyrotechnic systems
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In order to investigate relative reactivity of different oxidants in solid-state reactions of pyrotechnic mixtures, thermal properties of Sn + Sr(NO3)2, Sn + Ba(NO3)2, and Sn + KNO3 pyrotechnic systems have been studied by means of TG, DTA, and DSC methods and the results compared with those of pure oxidants. The apparent activation energy (E), ΔG No, ΔH No, and ΔS No of the combustion processeswere obtained from the DSC experiments. The results showed that the nat ure of oxidant has a significant effect on ignition temperature, and thekinetic of the pyrotechnic mixtures' reactions, and the relative reacti vity of these mixtures was found to obey in the following order: Sn + Sr(NO3)2 > Sn + Ba(NO 3)2 > Sn+ KNO3.
- Hosseini, Seyed Ghorban,Eslami, Abbas
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p. 1111 - 1120
(2011/01/07)
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- Two variants of the 1/2[110]p(203)p crystallographic shear structure: The phasoid Sr0.61Pb0.18(Fe 0.75Mn0.25)O2.29
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For the composition (Sr0.61 Pb0.18)(Fe 0.75Mn0.25)O2.29, a new modulated crystallography shear structure, related to perovskite, has been synthesized and structurally characterized by transmission ele
- Lepoittevin, Christophe,Hadermann, Joke,Malo, Sylvie,Perez, Olivier,Van Tendeloo, Gustaaf,Hervieu, Maryvonne
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p. 8257 - 8262
(2009/12/08)
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- Strontium silylamides, adducts thereof with Lewis bases, preparation thereof and deposition of strontium thin films
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Compound of the formula (I): wherein R represents a radical chosen from methyl or ethyl, and n is an integer equal to 1, 2 or 3. Its use in semiconductor manufacturing, as a thin film precursor and a method of its deposition on a substrate.
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Page/Page column 6
(2008/12/08)
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- Metal Complex Compound Comprising B-Diketonato Ligand
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[PROBLEMS] To provide a metal complex compound capable of being suitably used for manufacturing a metal-containing thin film by the CVD method and a method for preparing a metal-containing thin film. [MEANS FOR SOLVING PROBLEMS] A metal complex compound comprising a β-diketonato ligand having an alkoxyalkyl-methyl group, and a method for preparing a metal-containing thin film using the metal complex compound by the CVD method.
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Page/Page column 22
(2008/12/04)
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- Partially hydroxylated polycrystalline ionic oxides: A new route toward electron-rich surfaces
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Charge traps at the surface of oxide materials play a fundamental role in various chemical processes, such as the activation of supported metal clusters. In this study, combining electron paramagnetic resonance with cluster model DFT calculations, we show that excess electrons at the surface of MgO, CaO, and SrO polycrystalline materials can be generated by preparing weakly hydroxylated surfaces followed by deposition of small amounts of alkali metals. The residual OH groups present on specific sites of the partially dehydroxylated surface act as stable traps for electrons donated by the alkali metal (Na in this case) which forms a Na+ ion distant from the trapped electron. This process results in the formation of thermally stable (H+)(e_) color centers at the surface of the oxide. The procedure could be of interest for the stabilization and activation of supported metal nanoparticles with potential use in catalysis.
- Napoli, Francesco,Chiesa, Mario,Giamello, Elio,Finazzi, Emanuele,Di Valentin, Cristiana,Pacchioni, Gianfranco
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p. 10575 - 10581
(2008/02/12)
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- Reduction of benzaldehyde on alkaline earth metal oxides
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Benzaldehyde reduction was studied over alkaline earth metal oxide catalysts and carried out in a nitrogen or a dihydrogen atmosphere at the 100-350 °C of the range reaction temperature. The results show that benzyl alcohol is produced by the Cannizzaro reaction under nitrogen flow on MgO oxide and by direct hydrogenation under dihydrogen on irreducible oxides such as CaO, BaO and SrO. The Cannizzaro reaction involves the basic hydroxyl groups and is followed by the reduction of benzoate species by H2 to benzaldehyde. Toluene and benzene were produced at high reaction temperature under N2 flow over alkaline earth oxides from a reaction involving benzylate species. Under H2 flow, toluene and benzene were also formed by means of consecutive reduction reactions. The present work deals with the acid-base properties of alkaline earth metal oxide catalysts (MgO, CaO, BaO, SrO) and benzaldehyde reduction was used as probe reaction for characterizing the surface properties.
- Saadi,Rassoul,Bettahar
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- Structural chemistry and metamagnetism of an homologous series of layered manganese oxysulfides
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An homologous series of layered oxysulfides Sr2MnO 2Cu2-mδSm+1 with metamagnetic properties is described. Sr2MnO2Cu2-δ-S2 (m = 1), Sr2MnO2Cu4-δS3 (m = 2) and Sr2MnO2Cu6-δS4 (m = 3), consist of MnO2 sheets separated from antifluorite-type copper sulfide layers of variable thickness by Sr2+ ions. All three compounds show substantial and similar copper deficiencies (δ ≈ 0.5) in the copper sulfide layers, and single-crystal X-ray and powder neutron diffraction measurements show that the copper ions in the m = 2 and m = 3 compounds are crystallographically disordered, consistent with the possibility of high two-dimensional copper ion mobility. Magnetic susceptibility measurements show high-temperature Curie-Weiss behavior with magnetic moments consistent with high spin manganese ions which have been oxidized to the (2+δ)+ state in order to maintain a full Cu-3d/S-3p valence band, and the compounds are correspondingly p-type semiconductors with resistivities around 25 Ω cm at 295 K. Positive Weiss temperatures indicate net ferromagnetic interactions between moments. Accordingly, magnetic susceptibility measurements and low-temperature powder neutron diffraction measurements show that the moments within a MnO2 sheet couple ferromagnetically and that weaker antiferromagnetic coupling between sheets leads to A-type antiferromagnets in zero applied magnetic field. Sr 2MnO2Cu5.5S4 and Sr 2MnO2CU3-5S3 are metamagnets which may be driven into the fully ordered ferromagnetic state below 25 K by the application of fields of 0.06 and 1.3 T respectively. The relationships between the compositions, structures, and physical properties of these compounds, and the prospects for chemical control of the properties, are discussed.
- Gal, Zoltan A.,Rutt, Oliver J.,Smura, Catherine F.,Overton, Timothy P.,Barrier, Nicolas,Clarke, Simon J.,Hadermann, Joke
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p. 8530 - 8540
(2007/10/03)
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- Bi12Sr22Fe11O56: A new form of 2 2 0 1/0 2 0 1 terraces like structures, terms like m = 6, n = 11 of the [BiO2]m[Sr2FeO 4]n family
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A new oxide, namely Bi12Sr22Fe11O 56, has been isolated in the Bi-Sr-Fe-O system. The transmission electronic microscopy studies carried out have permitted to characterise it as a double collapsed member derived from the regular intergrowth 2 2 0 1/0 2 0 1 type structure Bi2Sr4Fe2O10 (J. Solid State Chem. 118 (1995) 227). It crystallises in the space group I2/a with the following parameters: a=38.82(1)A,b=5.731(2),c=38.35(1)A and β=121.31(2)°. Close relationships with the collapsed structure Bi 13Ba2Sr25Fe13O66 (m=7,n=13) are shown. This new ferrite can be described as the (m=6,n=11) member of the [Bi2O2]m[Sr2FeO 4]n family. The stairs are then 6 bismuth atoms wide and the K2NiF4 layers are 11 FeO6 octahedra thick. Moreover, the high-resolution electron microscopy images show the presence of local defects leading to the (m=7,n=11) member. Another description of this structure is also considered: it can be understood as slices of the parent structure, Bi2Sr4Fe2O10, separated by shearing zones. If the last ones seem to be the same in all the members, the thickness of the first ones can vary and so leading to different members of the new [Bi2Sr4Fe2O10]w [Bi4Sr6Fe3O16] family.
- Allix, Mathieu,Pelloquin, Denis,Raveau, Bernard
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p. 1133 - 1138
(2008/10/09)
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- Synthesis, structure, and magnetic properties of Sr2NiOsO 6 and Ca2NiOsO6: Two new osmium-containing double perovskites
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Two new double perovskite oxides, Ca2NiOsO6 and Sr2NiOsO6, have been prepared as polycrystalline powders by solid state synthesis. The two oxides were structurally characterized by variable-temperature powder neutron diffraction. Ca2NiOsO6 was found to adopt a monoclinic structure (P21/n), while Sr 2NiOsO6 was found to be tetragonal (I4/m). Magnetic susceptibility measurements indicate that Ca2NiOsO6 orders in a canted antiferromagnetic state at about 175 K while Sr 2NiOsO6 orders antiferromagnetically at about 50 K.
- Macquart, Rene,Kim, Seung-Joo,Gemmill, William R.,Stalick, Judith K.,Lee, Yongjae,Vogt, Tom,Zur Loye, Hans-Conrad
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p. 9676 - 9683
(2008/10/09)
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- Synthesis and properties of the layered perovskite phase Sr 3Mo1.5Zn0.5O7-δ
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The new layered perovskite phase Sr3Mo1.5Zn 0.5O7-δ was synthesized by solid state reaction using a Zn/ZnO oxygen buffer. The crystal structure was refined from X-ray powder pattern by the Rietveld method. The compound crystallizes tetragonal in the space group I4/mmm (no. 139) with the lattice parameters a = 3.9631(3) A, c = 20.583(1) A. An oxygen deficiency corresponding to δ ≈ 0.25 was determinated, indicating the presence of molybdenum in mixed valence(Mo4+ and Mo6+).
- Steiner, Udo,Reichelt, Werner,Schmidt, Marcus,Schnelle, Walter
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p. 649 - 654
(2008/10/09)
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- Thermal decomposition of metal nitrates in air and hydrogen environments
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The decomposition of metal nitrates in air has been systematically studied by thermogravimetry. Observed temperature of decomposition (Td) have been inversely correlated to the charge densities (CD) of the metal cations. Due to a back-donation of electronic cloud from the nitrate to an unfilled d-orbital of transition and noble metals, their nitrates generally exhibited lower TdS ( 850 K). The thermal stability/reducibility of metal nitrates in an hydrogen atmosphere has also been studied by temperature-programmed reduction (TPR). Observed reduction temperatures (Tr) for nitrates of the base metals and the noble metals are lower than their Td, i.e., Tr d. The lowering of Tr might be attributed to a spillover of hydrogen to a nitrate moiety through heterolytic (ionic) and homolytic (atomic) dissociation of hydrogen on the respective base and noble metals. The stoichiometry of hydrogen consumption, quantitatively measured from TPR, varied with the group of metal cations. According to the stoichiometry, the end product in the TPR reduction was NH3 (NH2/NNO3-a??4.4) and N2 (NH2/NNO3-a??2.4) for nitrates of the noble and base metals, respectively. The Trs for nitrates of the transition metals are often a??20 K higher than their Tds, and the ratio NH(2)/NNO3- varies widely between 0.7 and 3.2. Their reduction may be triggered by thermal decomposition.
- Yuvaraj, Shanmugam,Lin, Fan-Yuan,Chang, Tsong-Huei,Yeh, Chuin-Tih
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p. 1044 - 1047
(2007/10/03)
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- Large effects of A-site average cation size on the properties of the double perovskites Ba2-xSrxMnReO6: A d5-d1 system
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Ba2-xSrxMnReO6 (x = 0, 0.5, 1, 2) phases with a double-perovskite structure were prepared by solid-state techniques in evacuated sealed silica tubes. Mn2+ and Re6+ are virtually completely ordered on the B sites. The compounds are ferrimagnetic below 120 K. The maximum saturation moment was obtained for a compound with x = 0.5 whose tolerance factor is closest to 1. The whole series of compounds, 0.0≤x≤2.0, exhibits semiconducting behavior with variable-range hopping type of conduction. Sr2MnReO6 has an unusually high coercive field (2.6 T at 5 K) and two transitions in the M-H loop. Ba2MnReO6 shows large positive magnetoresistance (14% at 80 K, 5 T) below 140 K, while the other compositions studied exhibit negative magnetoresistance in the temperature range measured.
- Popov, Guerman,Greenblatt, Martha
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- Structural investigations of ACu3Ru4O12 (A=Na, Ca, Sr, La, Nd) - A comparison between XRD-Rietveld and EXAFS results
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The structures of five perovskite-related oxides with the general composition ACu3Ru4O12 with A = Na, Ca, Sr, La and Nd, have been examined both by XRD-Rietveld refinements and Ru-K EXAFS-spectroscopy. In addition, the behavior on reduction was investigated by thermogravimetry (TG). The TG measurements revealed that the composition was almost exactly A1Cu3Ru4O12 for all samples. The inter-atomic distances derived from EXAFS- and XRD-Rietveld fits show an excellent agreement with differences smaller than 8 mA even for R > 5 A. All inter-atomic distances increase in the order NaA-cation. The experimentally found distances are compared with the corresponding values expected from bond-valence calculations.
- Ebbinghaus,Weidenkaff,Cava
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p. 126 - 136
(2008/10/08)
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- New layered manganese oxide halides
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The first layered manganese(III) oxide chlorides, Sr2MnO3Cl and Sr4Mn3O8-yCl2, have been synthesised; Sr2MnO3Cl adopts a K2NiF4 type structure with sheets of MnO5 square based pyramids linked through oxygen and separated by SrCl layers; it is the end member of a new family of Ruddlesden-Popper type manganese oxide halides which includes the three-layer member Sr4Mn3O8-yCl2 also reported herein.
- Knee, Christopher S.,Weller, Mark T.
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p. 256 - 257
(2007/10/03)
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- The superconductor (Tl,Hg,Ca)2- (Ba,Sr)2(Ca,Sr,Tl)Cu2O7.6
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The crystal structure of superconductor (Tl,Hg,Ca)2-(Ba,Sr)2(Ca,Sr,Tl)Cu2O7.6 was investigated. The compound contained both Tl and Hg in the charge reservoir (CR), Sr is located at both alkali-earth (AE) metal
- Valldor, Martin,Bryntse, Ingrid,Morawski, Andrzej
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p. i126-i128
(2007/10/03)
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