- New multicomponent fluoride glasses
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New glass compositions have been investigated in the barium-, indium- and gallium-based glass system (BIG). Radioactive thorium has been completely removed and replaced by gadolinium, and these new glasses have been stabilized by substituting barium by al
- Fogret,Charron,Fonteneau,L'Helgoualch,Lucas
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- Thermal stabilities of americium and cerium tetrafluorides
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The thermal stabilities of americium and cerium tetrafluorides were determined by mass spectrometry, monitoring their gaseous vaporization and/or decomposition products as a function of temperature. For americium tetrafluoride, the dominant high temperature (less than or equal to 700°C) process is thermal decomposition to the trifluoride. In contrast, with cerium tetrafluoride, the most prominent process at high temperature (less than or equal to 850°C) is congruent sublimation. The results of these studies are interpreted in terms of the relevant thermodynamic parameters for each process and are compared with predictions and results which have been reported in the literature.
- Gibson,Haire
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- Pseudotetragonal structure of Li2+xCex 3+Ce12-x4+F50: The first mixed valence cerium fluoride
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The crystal structure of the new Li5.5Ce12F 50 compound has been fully characterized by single-crystal and synchrotron powder X-ray diffraction. An accurate pseudotetragonal structure was described In the monoclinic P21 space group with 68 independent crystallography sites. The Li5.5Ce12F50 composition belongs to the Li2+xCex3+Ce 12-x4+F60 solid solution. Its structure consists of an opened fluorine framework where a channel network allows the intercalation of relatively mobile lithium cations, inducing the formation of the mixed-valence cerium (the intercalation of Li+ leads to the reduction of a part of Ce4+ to Ce3+). One part of the lithium ions, necessary for the electroneutrality of the tetravalent equivalent cerium fluoride (Li2Ce12F50 composition), is in a locked fluorine polyhedron. Only the supplementary x amount of lithium is able to be exchanged in Li2+xCex3+Ce 12-x4+F50. The structure of Li 2+xCex3+Ce12-x4+F 50 is a rearrangement, due to lithium intercalation, of the base CeF4 structure. Bond valence calculation on Ce sites, Ce coordination polyhedra volumes, and a calculated Ce cationic radius give the indication of a partial long-range ordering of trivalent and tetravalent cerium cations In specific slabs of the structure. 7Li NMR spectroscopy and XPS analyses have confirmed all of the structure details.
- Renaudln, Guillaume,Dleudonne, Belto,Avignant, Daniel,Mapemba, Elise,El-Ghozzi, Malika,Fleutot, Solene,Martinez, Herve,Cerny, Radovan,Dubois, Marc
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- 19F high magnetic field NMR study of β-ZrF4 and CeF4: From spectra reconstruction to correlation between fluorine sites and 19F isotropic chemical shifts
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High magnetic field and high spinning frequency one- and two-dimensional one-pulse MAS 19F NMR spectra of β-ZrF4 and CeF 4 were recorded and reconstructed allowing the accurate determination of the 19F chemical shift tensor parameters for the seven different crystallographic fluorine sites of each compound. The attributions of the NMR resonances are performed using the superposition model for 19F isotropic chemical shift calculation initially proposed by Bureau et al. (Bureau, B.; Silly, G.; Emery, J.; Buzare, J.-Y. Chem. Phys. 1999, 249, 85-104). A satisfactory reliability is reached with a root-mean-square (rms) deviation between calculated and measured isotropic chemical shift values equal to 1.5 and 3.5 ppm for β-ZrF4 and CeF4, respectively.
- Legein,Fayon,Martineau,Body,Buzare,Massiot,Durand,Tressaud,Demourgues,Peron,Boulard
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- Tetraammine Tetrafluorido Cerium(IV) Ammonia (1/1), [CeF 4(NH3)4] · NH3
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The synthesis and crystal structure of the first ammine complex of a cerium fluoride, tetraammine tetrafluorido cerium(IV) ammonia (1/1), [CeF 4(NH3)4] · NH3, are presented. The compound crystallizes in the form of colorless, block-shaped single crystals in the tetragonal space group P4/ncc with a = 9.03215(9), c = 10.96404(17) A , V = 894.443(19) A3, and Z = 4. The compound contains discrete [CeF4(NH3)4] molecules interconnected by N-H·F hydrogen bonds.
- Kraus, Florian,Baer, Sebastian A.
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- Synthesis and structure of Ag7M6F31 (M = Zr, Hf, Ce)
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Colorless single crystals of Ag7Zr6F31 have been obtainend by heating up a mixture of AgF and ZrF4 in a closed goldtube (T = 450 °C, t ~ 2d). The compound crystallizes trigonal, space group R3?-C23i (No. 148) with a = 1400,9(3) pm, c = 979,0(2) pm, Z = 3. Also prepared were the isotypic compounds Ag7Hf6F31 with a = 1393,8(2) pm, c = 978,7(2)pm, and Ag7Ce6F31 with a = 1469,8(1) pm, c = 998,5(1) pm.
- Koller,Müller
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p. 1426 - 1428
(2008/10/08)
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- Au[AuF4]2 - An unexpected by-product in the system MF4/AuF3 and single crystals of CeF4, a further by-product
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Investigating the system MF4/AuF3 (M = Th4+, Ce4+) we obtained unexpectively Au[AuF4]2 in form of irregular, brown single crystals. It crystallizes monoclinic, space group P21/n (No. 14) with a = 527.21(7) pm, b = 1070.76(10) pm, c = 573.48(7) pm, β= 90.633(14)°, Z = 2, isotypic with Ag[AuF4]2 and Pd[AuF4]2. As a further by-product we obtained for the first time colourless single crystals of CeF4 (monoclinic, C2/c, No. 15, a = 1258.83(8) pm, b = 1062.63(8) pm, c = 822.41(9) pm, β = 126.24(1)°, and Z = 12).
- Schmidt,Müller
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p. 605 - 608
(2008/10/08)
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