- Study on the stability of GaF3-based glasses by differential scanning calorimetry
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The glass formation and devitrification of GaF3-based glasses were studied by differential scanning calorimetry. A comparison of various simple quantitative methods to assess the level of stability of multi-component fluoride glass systems is presented. Most of these methods are based on critical temperatures. In this paper a new parameter kb(T) is added to the stability criteria. The stability of several GaF3-based glasses were experimentally evaluated and correlated with the activation energies of crystallization via this new kinetic criterion and compared with those evaluated by other criteria.
- Zhu,Jin,Dong,Qiang,Ma
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- Structural and magnetochemical studies on KCuGaF6
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The crystal structure of KCuGaF6 was determined on the base of X-ray single crystal data (wR2 = 0.084 for 2476 independent reflections). The compound crystallizes with a = 728.56(4), b = 989.51(6), c = 676.27(3) pm, β = 93.120(5)°, Z = 4 in space group P21/c of the pyrochlore related KCuCrF6 type. The octahedral coordinations [GaF6] and [CuF6] are slightly resp. strongly distorted (mean values Ga-F: 188.2pm resp. Cu-F: 188.2/200.1/ 227.6 pm). The longest distances Ga-F and the shortest ones Cu-F are found within octahedral chains of these two kinds of atoms, running along [100] and [001], resp., and being mutually bridged as well (M-F-M in between 114 and 145°). The magnetic mole susceptibilities measured at powders and at a single crystal follow the isotropic Heisenberg model for S = 1/2, if effects of chain disrupture are considered in the form of some paramagnetic portion. No indication of threedimensional magnetic order is observed down to T = 2 K and low magnetic fields H 6 (J/k = -71 K for the powder) is distinguished this way from the chain structure compounds KCuAlF6 und Na2CuScF7 (J/k = -76 resp. -59 K) which were also magnetically studied and yield similar antiferromagnetic exchange constants J/k.
- Dahlke,Pehler,Babel
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- Recognition on systems RbF-GaF3 and CsF-GaF3
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The systems RbF-GaF3 and CsF-GaF3 were re-investigated by DTA and XRD method. In the system RbF-GaF3, with eutectic E1 at 750°C in the location of 8.5 mol% GaF3 and E2 at 749°C in the location of 43.0 mol% GaF3, three compounds Rb3GaF6, RbGaF4 and RbF·2GaF3 were identified and indexed by XRD. The indexed result of α-Rb3GaF6 could not be successfully obtained, β-Rb3GaF6 is tetragonal, a = 6.324±0.004, c = 8.860±0.003 A?. RbGaF4 is orthorhombic, a = 9.821 ± 0.006, b = 9.517 ± 0.005, c = 8.060 ± 0.006 A?; RbF·2GaF3 is also orthorhombic, a = 9.459 ± 0.005, b = 9.336 ± 0.005, c = 7.685 ± 0.005 A?. In the system CsF-GaF3, with eutectic E1 at 66C in the location of 7.5 mol% GaF3 and E2 at 675°C in the position of 44.0 mol% GaF3, two compounds were confirmed. α-Cs3GaF6 is orthorhombic with a = 10.62 ± 0.02, b = 9.959 ± 0.006 and c = 5.607 ± 0.005 A?; β-Cs3GaF6 is also orthorhombic, a = 10.356 ± 0.003, b = 8.280 ± 0.003, c = 7.621 ± 0.005 A?; γ-Cs3GaF6 is tetragonal, a = 6.833 ± 0.003, c = 9.869 ± 0.002 A?; CsGaF4 is orthorhombic, a = 8.571 ± 0.007, b = 7.575 ± 0.007 and c = 6.981 ± 0.006 A?. (C) 2000 Elsevier Science B.V.
- Chen,Zhang
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- Quantum-chemical calculations and IR spectra of the (F2)MF 2 molecules (M = B, Al, Ga, In, Tl) in solid matrices: A new class of very high electron affinity neutral molecules
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Electron-deficient group 13 metals react with F2 to give the compounds MF2 (M = B, Al, Ga, In, Tl), which combine with F 2 to form a new class of very high electron affinity neutral molecules, (F2)MF2, in solid argon and neon. These (F 2)MF2 fluorine metal difluoride molecules were identified through matrix IR spectra containing new antisymmetric and symmetric M-F stretching modes. The assignments were confirmed through close comparisons with frequency calculations using DFT methods, which were calibrated against the MF3 molecules observed in all of the spectra. Electron affinities calculated at the CCSD(T) level fall between 7.0 and 7.8 eV, which are in the range of the highest known electron affinities.
- Wang, Xuefeng,Andrews, Lester
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p. 3768 - 3771
(2011/04/26)
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- Structural and magnetochemical studies of Ba5Mn3F19 and related compounds AII5MIII3F19
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Single crystal structure determinations by X-ray methods were performed at the following compounds, crystallizing tetragonally body-centred (Z = 4): Sr5V3F19 (a = 1423.4(2), c = 728.9(1) pm), Sr5Cr3F19 (a = 1423.5(2), c = 728.1(1) pm), Ba5Mn3F19 (a =1468.9(1), c =770.3(1) pm, Ba5Fe3F19 (a =1483.5(1), c =766.7 (1) pm), and Ba5Ga3F19 (a = 1466.0(2), c = 760.1(2) pm). Only Ba5Mn3F19 was refined in space group I4cm (mean distances for elongated octahedra Mn1-F: 185/207pm equatorial/axial; for compressed octahedra Mn2-F: 199/182 pm), the remaining compounds in space group I4/m. In all cases the octahedral ligand spheres of the M1 atoms showed disorder, the [M1F6] octahedra being connected into chains in one part of the compounds and into dimers in the other. The magnetic properties of the V, Cr and Mn compounds named above and of Pb5Mn3F19 and Sr5Fe3F19 as well were studied; the results are discussed in context with the in part problematic structures.
- Dahlke,Graulich,Welsch,Pebler,Babel
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p. 1255 - 1263
(2008/10/08)
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- On X-ray single crystal studies of Na2FeAlF7, Na2MIIGaF7 (MII = Ni, Zn), and Na2ZnFeF7 and the Structural Chemistry of Weberites
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At single crystals of the orthorhombic weberite Na2NiGaF7 (a = 716.1, b = 1021.6, c = 740.9 pm; Imma, Z = 4) and of the monoclinic variants (C2/c, Z = 16) Na2FeAlF7 (a = 1242.6, b = 727.8, c = 2420.6 pm, β = 99.99°), Na2ZnGaF7 (a = 1251.9, b = 730.3, c = 2435.3 pm, β = 99.74°) and Na2ZnFeF7 (a = 1261.0, b = 7.359, c = 2453.8 pm, β = 99.70°) complete X-ray structure determinations were performed. The results and the influence of radii on the bridge angles MII-F-MII and MII-F-MIII are discussed in connection with general features within the structural chemistry of 28 weberites.
- Dahlke,Peschel,Babel
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p. 1003 - 1010
(2008/10/09)
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- X-ray structural studies of the polymorphic elpasolites K2LiAlF6 and Rb2LiGaF6
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At single crystals of low (LT) and high temperature (HT) modifications of K2LiAlF6 and of Rb2LiGaF6, synthesized at normal pressure (NP), the crystal structures were refined. LT-K2LiAlF6 is a cubic elpasolite (Fm3m, Z = 4, a = 784.2(1) pm; Al-F: 181.2(1) pm), HT-K2LiAlF6 and NP-Rb2LiGaF6 are isostructural with the hexagonalrhombohedral type of Cs2NaCrF6 (R3m, Z = 6, a = 561.7(1) resp. 586.3(1), c = 2757.6(6) resp. 2856.3(5) pm; mean values Al-F: 180.5 resp. Ga-F: 189.3 pm). A cubic high pressure modification (HP) of Rb2LiGaF6 was obtainable as a powder only (a = 820.8(2) pm). The relations of distances between LT/HT and HP/NP polymorphs of elpasolites are compared and discussed.
- Graulich,Drüeke,Babel
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p. 1460 - 1464
(2008/10/09)
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- InBF4, the First Complex Fluoride with Indium(I)
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InBF4 has been obtained for the first time by reaction of indium metal with anhydrous HF and BF3 in form of colourless, transparent single crystals. It crystallizes orthorhombic, space group Pnma - D162h (Nr. 62) with a = 919.1(2), b = 577.1(1) and c = 737.0(2) pm, Z = 4 and it is isotypic to KBF4 respectively to baryt-typ.
- Fitz,Mu?ller
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p. 579 - 582
(2008/10/09)
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- The first oligomeric anions of fluoro-litho metallates with octahedra sandwich motive: Cs4K{[F3MIIIF3]Li[F 3MIIIF3]}, MIII = Ga, Fe
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Colourless single crystals of Cs4K{Li[Ga2F12]} (A) and Cs4K{Li[Fe2F12]} (B) have been obtained by solid state reaction from intimate mixtures of the corresponding binary fluorides (Pt-tube, 750°C, 40 d). The trigonal unit cells with (A) a = 631,3(1) pm; c = 3059,9(6) pm and (B) a = 635,0(1) pm; c = 3089,2(7) pm, respectively (Z = 3, Guinier-Simon data, Cu-Kα1), are confirmed by single crystal investigations. The compounds crystalize isostructural in the space group R3m (No. 166). The structures were determined using four-circle diffractometer data (Siemens AED 2) with (A) R = 2.95%, 3627 Io and (B) R = 1.86%, 4179 Io, respectively (SHELX-76), and are characterized by triplets of facesharing octahedra parallel [00.1] with the cation-sequence MIII-Li-MIII, six of which are connected by [KF6]-octahedra via common corners and each triplet is surrounded by six different [KF6]-octahedra. The structure is completed by Cs+ filling the cavities. The Madelung Part of Lattice Energy (MAPLE), Mean Fictive Ionic Radii (MEFIR) and Effective Coordination Numbers (ECoN) are calculated and compared. The classification as lithometallate could be verified by a new MAPLE concept. The Charge Distribution (CHARDI) was calculated and compared with the results according to 'bond length-bond strength'. Johann Ambrosius Barth 1996.
- Bork,Hoppe
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p. 297 - 307
(2008/10/09)
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- The Crystal Structure of LiPdGaF6, RbPdAlF6 and K1.06Pd0.95Fe1.05F6
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Single crystals of LiPdGaF6 (blue; trigonal, P3-1C-D(2)3d (No. 163), a=505.72(2), c=923.7(2) pm; LiCaAlF6-Type [1]), RbPdAlF6 (violet; orthorhombic, PNMA-D(16)2h (No. 62), a=729.0(1), b=711.1(1), c=1006.5(2) pm; CsAgFeF6-Type [2]) and K1.06Pd0.95Fe1.05F6 (greenish-blue; tetragonal, P42/MBC-D(13)4h (No.135), a=1279.07(7), c-800.2(1) pm; K1.08MnFeF6-Type [3]; four cycle diffractometer data, Siemens AED2) are obtained by heating the binary fluorides in sealed Pd-tubes under dry argon [solid state reaction, T~650, t~ 19 d) (39 d, 24 d)].
- Mueller, Markus,Mueller, Bernd G.
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- Blue and green upconversion in Er3+-doped fluoroindate glasses
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The upconversion properties of Er3+ in fluoroindate bulk glasses (composition: 40InF3-20ZnF2-16BaF2-(20-x) SrF2-2GaF3-2NaF-xErF3 with x=1, 2, 3, and 4 mole %) are investigated, following 4F9/2 excitation with a red krypton laser. A strong green and a weaker blue luminescence is observed at room temperature corresponding to emissions from the thermally coupled 4S3/2 and 2H11/2 bands and the 2H9/2 level respectively. Resonant energy transfer processes involving two excited erbium ions and a two-step absorption process are proposed to explain the upconversion phenomena. The emission intensities depend on the excitation power as Pexcn with 1.5 ≤n≤1.7 for the green and 1.6 ≤n≤1.9 for the blue emission. The decay times and the relative intensities of the luminescences are also studied as a function of Er3+ concentration.
- Reiche,Nunes,Carvalho,Messaddeq,Aagerter
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p. 773 - 777
(2008/10/08)
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- Crystal structure of the metastable form of aluminum trifluoride β-AlF3 and the gallium and indium homologs
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The crystal structure of the metastable phase β-AlF3, which is related to the hexagonal tungsten bronze structure, has been solved by X-ray powder and single-crystal diffraction methods. The crystal habit is pseudo-hexagonal with systematic twinning (rotation of 120° around the c axis), but the true symmetry is orthorhombic. The network is built from very regular AlF6 octahedra rotated by approximately 7.2° from the positions of the ideal HTB structure. A similar network, with the same propagation of the tilting, was observed in the compound (H2O)0.33FeF3 and in the metastable polymorphs of CrF3 and of VF3.
- Bail, A. le,Jacoboni, C.,Leblanc, M.,Pape, R. de,Duroy, H.,Fourquet, J. L.
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