- Electron microscopy, spectroscopy, and first-principles calculations of Cs2O
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Oxides of cesium play a key role in ameliorating the photoelectron emission of various opto-electronic devices. However, due to their extreme reactivity, their electronic and optical properties have hardly been touched upon. With the objective of better understanding the electronic and optical properties of Cs2O in relationship to its structure, an experimental and theoretical study of this compound was undertaken. First-principles density functional theory calculations were performed. The preferred structural motif for this compound was found to be anti-CdCl2. Here three Cs-O-Cs molecular layers are stacked together through relatively weak van-der-Waals forces. The energy bands were also calculated. The lowest transition at 1.45 eV, was found to be between the K point in the valence band to the Γ point in the conduction band. A direct transition at 2 eV was found in the center (Γ) of the Brillouin zone. X-ray powder diffraction, transmission electron microscopy and selected area electron diffraction were used to analyze the synthesized material. These measurements showed good agreement with the calculated structure of this compound. Absorption measurements at 4.2 K indicated two optical transitions with somewhat higher energy (indirect one at 1.65 and a direct transition at 2.2 eV, respectively). Photoluminescence measurements also showed similar transitions, suggesting that the lower indirect transition is enhanced by three nearby minima at 1.5 eV in the Brillouin zone.
- Gemming,Seifert,Muehle,Jansen,Albu-Yaron,Arad,Tenne
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- Homoatomic Stella Quadrangula [Tl8]6 in Cs 18Tl8O6, Interplay of SpinOrbit Coupling, and JahnTeller Distortion
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Cs18Tl8O6 was synthesized reacting the binary compounds CsTl and Cs2O. According to single crystal X-ray analysis, the title compound crystallizes as a novel structure type in the cubic space group I23 and is diamagnetic. The electronic structure of the extended solid and of excised Cs6Tl8 clusters has been examined by relativistic density functional calculations including spin-orbit coupling. Cs18Tl8O6 comprises a clusteranion [Tl 8]6- in the shape of a tetrahedral star. An isoelectronic cluster was found previously in Cs8Tl8O, however, with the shape of a parallelepiped. Both clusteranions can be derived from a homocubane unit by displacive distortions. It has been shown by quantum mechanical analyses that the closed-shell electronic structure of the parallelepiped is the result of a Jahn-Teller distortion, while in contrast the tetrahedral star in Cs 18Tl8O6 would still exhibit an open-shell degenerate HOMO within a scalar relativistic approximation. Only if spin-orbit coupling is considered, a closed-shell electronic system is obtained in accordance with the diamagnetic behavior of Cs18Tl8O 6.
- Wedig, Ulrich,Saltykov, Vyacheslav,Nuss, Juergen,Jansen, Martin
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- The suboxometallates A9MO4 (A = Rb, Cs; M = Al, Ga, In, Fe, Sc)
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Single crystals of the suboxometallates A9MO4 (A = Rb, Cs; M = Al, Ga, Fe, Sc) were prepared by reaction of stoichiometric mixtures of M2O3 with alkali metals and their oxides A 2O. They crystallize i
- Hoch, Constantin,Bender, Johannes,Wohlfarth, Andreas,Simon, Arndt
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- Preparation of Cs2ZrO3 and Cs2ThO3 through sol-gel method and their characterization
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Cesium zirconate and cesium thorate were prepared by sol-gel method following citrate-nitrate route. The compounds were characterized by X-ray diffraction, chemical analysis and simultaneous TG-DTA. The methods of preparation of Cs2ZrO3/s
- Mishra,Ali,Bharadwaj,Das
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- Alkali Metal Suboxometalates-Structural Chemistry between Salts and Metals
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The crystal structures of the new cesium-poor alkali metal suboxometalates Cs10MO5 (M = Al, Ga, Fe) show both metallic and ionic bonding following the formal description (Cs+)10(MO45-)(O2-)·3e-. Comparable to the cesium-rich suboxometalates Cs9MO4 (M = Al, Ga, In, Fe, Sc) with ionic subdivision (Cs+)9(MO45-)·4e-, they contain an oxometalate anion [MIIIO4]5- embedded in a metallic matrix of cesium atoms. Columnlike building units form with prevalent ionic bonding inside and metallic bonding on the outer surface. In the cesium-rich suboxometalates Cs9MO4, additional cesium atoms with no contact to any anion are inserted between columns of the formal composition [Cs8MO4]. In the cesium-poor suboxometalates Cs10MO5, the same columns are extended by face-sharing [Cs6O] units, and no additional cesium atoms are present. The terms "cesium-rich" and "cesium-poor" here refer to the Cs:O ratio. The new suboxometalates Cs10MO5 crystallize in two modifications with new structure types. The orthorhombic modification adopts a structure with four formula units per unit cell in space group Pnnm with a = 11.158(3) ?, b = 23.693(15) ?, and c = 12.229(3) ? for Cs10AlO5. The monoclinic modification crystallizes with eight formula units per unit cell in space group C2/c with a = 21.195(3) ?, b = 12.480(1) ?, c = 24.120(4) ?, and β = 98.06(1)° for Cs10AlO5. Limits to phase formation are given by the restriction that the M atoms must be trivalent and by geometric size restrictions for the insertion of [Cs6O] blocks in Cs10MO5. All of the suboxometalate structures show similar structural details and form mixed crystal series with statistical occupation for the M elements following the patterns Cs9(M1xM21-x)O4 and Cs10(M1xM21-x)O5. The suboxometalates are a new example of ordered intergrowth of ionic and metallic structure elements, allowing for the combination of properties related to both ionic and metallic materials. (Figure Presented).
- W?rsching, Matthias,Hoch, Constantin
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- Metal-insulator transition during oxidation of cesium films
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The oxidation of Cs films in the thickness range of 5 to 25 layers was investigated at 95 K using UPS and HREELS combined in situ. The whole film undergoes a metal to insulator transition at an oxygen dose equivalent to the formation of Cs2O, the normal oxide. This state is characterized through a single, somewhat broadened 2p line of O2- in UPS, the opening of a gap around EF (vanishing electronic losses as seen through HREELS), and the appearance of a strong Fuchs-Kliewer phonon intensity. Below this transition, i.e., in the range of suboxides, the Cs surface plasmon is observed with its energy shifting to small values as the metallic electron density gets diluted with O2 dose. Above the transition, the UP spectra change into multiplet spectra well known for Cs dioxygen species. The oxidation process can be described by a Cs → suboxides → Cs2O → peroxides sequence.
- Shi,Jacobi
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- Anomalous lattice parameter increase in alkali earth aluminium substituted tungsten defect pyrochlores
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The structures of the defect pyrochlores AAl0.33W1.67O6 where A=K, Rb or Cs have been investigated using X-ray and neutron powder diffraction methods as well as the ab initio modelling program VASP. The three cubic pyrochl
- Thorogood, Gordon J.,Kennedy, Brendan J.,Peterson, Vanessa K.,Elcombe, Margaret M.,Kearley, Gordon J.,Hanna, John V.,Luca, Vittorio
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- Preparation and structural characterization of stable Cs2O closed-cage structures
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(Figure Presented) Fullerene-like Cs2O nanoparticles were prepared by laser ablation of 3R-Cs2O powder in evacuated quartz ampoules. The Cs2O closed cages, such as the faceted nanoparticle shown in the picture, are remarka
- Albu-Yaron, Ana,Arad, Talmon,Popovitz-Biro, Ronit,Bar-Sadan, Maya,Prior, Yehiam,Jansen, Martin,Tenne, Reshef
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- Crystal structures of Rb2U2O7 and Rb 8U9O31, a new layered rubidium uranate
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Two alkali metal uranates Rb2U2O7 and Rb8U9O31 have been synthesized by solid state reaction at high temperature and their crystal structures determined from single crystal X-ray diffraction data, collected with a three circles Brucker SMART diffractometer equipped by Mo(Kα) radiation and a charge-coupled device (CCD) detector. Their structures were solved using direct methods and Fourier difference techniques and refined by a least-square method on the basis of F2 for all unique reflections, with R1=0.043 for 53 parameters and 746 independent reflections with I≥2σ(I) for Rb2U 2O7, monoclinic symmetry, space group P21/c, a=7.323(2)A, b=8.004(3)A, c=6.950(2)A, β=108.81(1)°, ρmes=6.56(3)g/cm3, ρcal=6.54(2)g/cm3, Z=2 and R1=0.036 for 141 parameters and 2065 independent reflections with I≥2σ(I) for Rb 8U9O31, orthorhombic, space group Pbna, a=6.9925(9)A, b=14.288(2)A, c=34.062(5)A, ρmes=6.47(3)g/ cm3, ρcal=6.48(2)g/cm3, Z=4. The Rb2U2O7 structure presents a strong analogy with that of K2U 2O7 and can be described by layers of distorted UO 2(O4) octahedra built from dimeric units of edge shared octahedra further linked together by opposite corners. In Rb8U 9O31 puckered layers are formed by the association of two different uranium polyhedra, pentagonal bipyramids and distorted octahedra. The structure of Rb8U9O31 is built from a regular succession of ∞1[U4O14]4- infinite ribbons similar to those observed in diuranates M2U2O7 (MK, Rb) and infinite three polyhedra wide ribbons ∞1[U5O21]12-, to create an original undulated sheets ∞2[U9O31]8-. For both compounds Rb+ ions occupy the interlayer space and exhibit comparable mobility with conductivity measurements indicating an Arrhenius-type behavior.
- Yagoubi,Obbade,Dion,Abraham
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- First isolated hypoelectronic [In6]6- cluster in insulating Cs22In6(SiO4)4
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Cs22In6(SiO4)4 was synthesized by the reaction of appropriate starting materials at 673 K, followed by slow cooling to room temperature, in arc-welded tantalum ampoules. According to single-crystal X-ray analysis, the compound crystallizes in a new structure type (P21/n(no. 14), a = 14.3533(4), b = 16.1712(4), c = 25.0135(7) A, β = 94.368(1), Z = 4), consisting of [In6]6- clusters with the shape of a distorted octahedron or more appropriately described as a condensate of three face sharing tetrahedra. The cluster is the first example of a hypoelectronic isolated [In6] 6- indium cluster. The oxosilicate indide can be regarded as a double salt , Cs6In6 on one hand and the oxosilicate Cs4SiO4 (× 4) on the other, which form the quaternary structure by inhomogeneous intergrowth of partial structures. The electronic structure of Cs22In6(SiO4) 4 was examined by DFT calculations and compared to the one of Rb 2In3, which exhibits linked In6 polyhedra. According to the DOS the title compound is a semiconductor with a band gap of 0.5 eV, which is in agreement with its observed insulating character. [In 6]6- is an isolated cluster bearing inert electron pairs at each vertex. In contrast, [In6]4- in Rb2In3 only exhibits inert pairs at the apical atoms. The four basal atoms are linked to neighboring clusters by covalent bonds forming a 2D network. These bonding scenarios are supported by the analysis of the projected density of states, the electron localization function and the partitioning of the electron density according to Bader. Copyright
- Saltykov, Vyacheslav,Nuss, Juergen,Wedig, Ulrich,Prasad, Dasari L. V. K.,Jansen, Martin
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- The standard molar enthalpy of formation of Cs2ZrO3
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The enthalpy of Cs2ZrO3 has been derived from its enthalpy of solution in HF*100H2O, as measured calorimetrically, in combination with auxiliary values.For the standard molar enthalpy of formation of Cs2ZrO3 the value ΔfH0m/sub
- Cordfunke, E. H. P.,Ouweltjes, W.,Vlaanderen, P. van
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- Cs10Tl6SiO4, Cs10Tl 6GeO4, and Cs10Tl6SnO3 - First oxotetrelate thallides, double salts containing "hypoelectronic" [Tl6]6- clusters
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Cs10Tl6TtO4 (Tt = Si, Ge) and Cs 10Tl6SnO3 were synthesized by the reaction of appropriate starting materials at 623-673 K, followed by fast cooling or quenching to room temperature, in arc
- Saltykov, Vyacheslav,Nuss, Juergen,Jansen, Martin
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- Cs3reIIIGe3O9 (RE = Pr, Nd, and Sm?Yb) and Cs8TbIII2TbIVGe9O27: A rare example of a mixed-valent Tb(III)/Tb(IV) oxide
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Single crystals of 12 new cesium rare earth germanates crystallizing in two new structure types were grown from a CsCl/CsF flux. Cs3REGe3O9 (RE = Pr, Nd, and Sm?Yb), a new family of germanates that form for almost the entire series of rare earth elements, crystallizes in orthorhombic space group Pna21 with lattice parameters in the following ranges: a = 13.7033(4)?14.022(2) ?, b = 7.0545(2)?7.2405(12) ?, and c = 12.6672(4)?12.836(2) ?. Surprisingly, the Tb reaction yielded both Cs3TbGe3O9 and Cs8Tb3Ge9O27, a rare example of a mixed-valent Tb(III)/ Tb(IV) compound. Cs8Tb3Ge9O27 crystallizes in space group P3 with the following lattice parameters: a = 11.2906(4) ?, and c = 7.9605(3) ?. The mixed-valent oxidation state of Tb was confirmed by structure solution, bond-valence sums, X-ray photoelectron spectroscopy data, and magnetic data. Optical and magnetic properties are reported for both sets of compounds.
- Morrison, Gregory,Spagnuolo, Nicholas R.,Karakalos, Stavros G.,Zur Loye, Hans-Conrad
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- From ∞1[(UO2)2O(MoO 4)4]6- to ∞ 1[(UO2)2(MoO4)3(MoO 5)]6- infinite chains in A6U2Mo 4O21 (A=Na, K, Rb, Cs) compounds: Synthesis and crystal structure
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A new caesium uranyl molybdate belonging to the M6U 2Mo4O21 family has been synthesized by solid-state reaction and its structure determined from single-crystal X-ray diffraction data. Contrary to the other alkali uranyl molybdates of this family (A=Na, K, Rb) where molybdenum atoms adopt only tetrahedral coordination and which can be formulated A6[(UO2)2O(MoO 4)4], the caesium compound Cs6U 2Mo4O21 should be written Cs 6[(UO2)2(MoO4)3(MoO 5)] with molybdenum atoms in tetrahedral and square pyramidal environments. Cs6[(UO2)2(MoO4) 3(MoO5)] crystallizes in the triclinic symmetry with space group P1 and a=10.4275(14) A, b=15.075(2) A, c=17.806(2) A, α=70.72(1)°, β=80.38(1)° and γ=86.39(1)°, V=2604.7(6) A3, Z=4, ρmes=5.02(2) g/cm 3 and ρcal=5.08(3) g/cm3. A full-matrix least-squares refinement on the basis of F2 yielded R 1=0.0464 and wR2=0.0950 for 596 parameters with 6964 independent reflections with I≥2σ(I) collected on a BRUKER AXS diffractometer with Mo(Kα) radiation and a CCD detector. The crystal structure of Cs compound is characterized by ∞ 1[(UO2)2(MoO4)3(MoO 5)]6- parallels chains built from U2O 13 dimeric units, MoO4 tetrahedra and MoO5 square pyramids, whereas, Na, K and Rb compounds are characterized by ∞1[(UO2)2O(MoO 4)4]6- parallel chains formulated simply of U2O13 units and MoO4 tetrahedra. Infrared spectroscopy measurements using powdered samples synthesized by solid-state reaction, confirm the structural results. The thermal stability and the electrical conductivity are also studied. The four compounds decompose at low temperature (between 540 and 610 °C).
- Yagoubi,Obbade,Saad,Abraham
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- Direct Z-scheme Cs2O-Bi2O3-ZnO heterostructures for photocatalytic overall water splitting
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In this work, a direct Z-scheme Cs2O-Bi2O3-ZnO heterostructure without any electron mediator is fabricated by a simple solution combustion route. Cs2O is chosen as a sensitizer to expand the light absorption range, and in addition, its conduction band minimum (CBM) and valence band maximum (VBM) positions are suitable to construct a direct Z-scheme system with ZnO and Bi2O3. Structural and elemental analyses show clear evidence for heterostructure formation. The Z-scheme charge carrier migration pathway in Cs2O-Bi2O3-ZnO is confirmed by high resolution XPS and ESR studies. The fabricated heterostructure exhibits a good ability to split water to H2 and O2 under simulated sunlight irradiation without any sacrificial agents or co-catalysts and has excellent photostability. The apparent quantum efficiency of the optimized Cs2O-Bi2O3-ZnO heterostructure reaches up to 0.92% at 420 nm. The excellent efficiency of this fabricated heterostructure is attributed to the efficient charge carrier separation, the high redox potential of the CBM and VBM benefiting from a direct Z-scheme charge carrier migration pathway and the extended light absorption range.
- Hezam, Abdo,Namratha,Drmosh,Ponnamma, Deepalekshmi,Nagi Saeed, Adel Morshed,Ganesh,Neppolian,Byrappa
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p. 21379 - 21388
(2018/11/20)
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- Bad-Metal-Layered Sulfide Oxide CsV2S2O
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Through a solid-state reaction between stoichiometric amounts of a mixed cesium oxide Cs2O1.3, VS, S, and V2O5, a polycrystalline powder of CsV2S2O was obtained. Small single crystals could be grown in a CsCl melt by allowing Cs2SO4, V metal and S powders to react. The crystals have a plate-like morphology, consistent with the tetragonal crystal-structure symmetry [P4/mmm, a = 3.9455(1), c = 7.4785(1) ?]. Magnetic measurements suggest that CsV2S2O is a temperature-independent paramagnet, and resistivity data concur with a bad metal. The mixed oxidation state of V on one crystallographic site offers a tentative explanation of the electronic properties of the title compound. CsV2S2O has a tetragonal crystal structure and contains Cs-separated V-S-O layers with relatively short V-V distances of 2.790 ?. V has formally a charge of +2.5, resulting in temperature-independent paramagnetism and bad-metal-like electric conductivity.
- Valldor, Martin,Merz, Patrick,Prots, Yurii,Schnelle, Walter
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- Characterization of oxides of cesium
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Cesium oxides are materials of great interest to the photodetection industry because of their relatively low work function (a??1 eV). Used mainly as coating films for photoemissive devices, they provide high wavelength thresholds and high photocurrents. However, they are unstable, air-sensitive, and hygroscopic, rendering them short-lived and limiting their applications. Although the technology of these devices is highly developed, their characterization on the micro- and nanoscale suffers from their poor chemical stability and poor crystallinity. In the present study, cesium oxides were synthesized from the elements and were characterized using a combination of chemical and structural analysis techniques. Because the reaction products were extremely sensitive to humidity, sample analysis without atmospheric exposure was essential, and techniques were developed for the transfer of the samples to the measurements systems. Extensive data obtained from X-ray energy-dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), X-ray diffraction (XRD), and Raman microscopy were obtained. Raman spectra with bands at 103, 742, and 1134 cm-1 strongly confirmed the presence of the oxide, peroxide, and Superoxide ions, respectively, as well as the absence of carbonate as an impurity. The A1g mode of Cs2O was detected as an anti-Stokes band at 103 cm-1. This study provides further insight into the reactivity of the various cesium oxides.
- Band,Albu-Yaron,Livneh,Cohen,Feldman,Shimon,Popovitz-Biro,Lyahovitskaya,Tenne
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p. 12360 - 12367
(2007/10/03)
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- Synthesis and crystal structure of CS3AuO2
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Bright orange single crystals of Cs3AuO2, sensitive to moisture and atmosphere, are obtained by reacting CsAu with a 1:1 molar mixture of Cs2O and CsO2 (CsAu: Cs2O:CsO2 = 3:2:2) in sealed silver crucibles under argon atmosphere at 380°C for a period of 6 days. The crystal structure (Pearsoncode mP72, P21/n, a = 1019.6(3), b = 1984.3(7), c = 1028.5(4) pm, β = 93.96(1)°, Z =12, 2562 reflections mit Io > 2ω(I), R1 = 0.0662, wR2 = 0.1660) is characterized by the presence of dumb-bell-shaped [O-Au-O]-moieties (d(Au-O) = 200,8(2) pm), a common feature of oxoaurates(I). WILEY-VCH Verlag GmbH, 2001.
- Mudring, Anja-Verena,Jansen, Martin
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- Teranry Oxides containing Anionic Gold
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The preparation and crystal structure of the novel ternary oxides M3AuO (M=Cs, Rb, K) containting anionic gold is reported. Cs3AuO (a=7.830(1) A, c=7.060(1) A) crystallizes as an hexagonal, Rb3AuO (a=5.501(1) A), K3AuO (a=5.240(1) A) as a cubic anti perovskite. Concerning to the ionic description (M(1+))3Au(1-)O(2-) in Cs3AuO gold exists as an anion. In Rb3AuO and K3AuO the anionic character of gold decreases respectively. The analysis of bond length and molar volumes gives support to this view, as well as investigations of conductivity and magnetic properties do.
- Feldmann, Claus,Jansen, Martin
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