- Structural Distortion in Perovskite Type KCaH3–xFx (0.54 ≤ x ≤ 3)
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Representatives of the solid solution series KCaH3–xFx were synthesized by solid state reactions from binary metal hydrides and fluorides. Crystal structures were analyzed by Rietveld refinement based on X-ray powder diffraction. The degree of substitution was determined by refinement of site occupancy factors as well as elemental analysis for hydrogen. Three sections of x in KCaH3–xFx can be distinguished. For x 3 and the solid solution starts only at x = 0.54. The tetragonal SrTiO3 type structure with partial ordering of hydrogen and fluorine atoms is found for 0.54 ≤ x ≤ 1.7. Both anion positions show mixed occupation with some preference of hydrogen atoms for 8h and fluorine atoms for 4a sites (I4/mcm, SrTiO3 type). For fluorine-rich compounds a solid solution with orthorhombic GdFeO3 type structure (Pnma) and a perfectly statistical distribution of hydrogen and fluorine atoms is found (1.8 ≤ x ≤ 3). Interatomic distances resulting from the structure refinements are in the range of typical K–H, K–F, Ca–H, and Ca–F distances for mainly ionic compounds.
- Kohlmann, Holger,Pflug, Christian
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- CsCaF3 - //xH//xSOLID SOLUTION (0 less than equivalent to x less than equivalent to 1. 70): STRUCTURAL CHARACTERISTICS AND HYDROGEN DIFFUSION INVESTIGATION.
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A study of the substitution of hydrogen for fluorine in CsCaF//3 shows the existence of a solid solution CsCaF//3// minus //x//H//x (0 less than equivalent to x less than equivalent to 1. 70) with cubic perovskite type structure. Both X-ray powder diffraction and wideline NMR show a statistical distribution of hydrogen and fluorine anions. The thermal evolution of the line width in the NMR spectra for **1H and **1**9F has been studied. The hydride ion is the only mobile one. Ionic-conductivity measurements seem to confirm a diffusion mechanism based on anionic hydrogen vacancies.
- Park,Senegas,Reau,Pezat,Darriet,Hagenmuller
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- Synthesis of high-purity calcium hydride
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A procedure for synthesizing high-purity calcium hydride in high yield was suggested. The admixture composition of the resulting CaH2 was determined by laser mass spectrometry.
- Bulanov,Troshin,Balabanov
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- Structural and vibrational properties of Ca2FeH6 and Sr2RuH6
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The structural and vibrational properties of the isostructural compounds Ca2FeH6 and Sr2RuH6 are determined by periodic DFT calculations and compared with their previously published experimental crystal structures as well as new experimental vibrational data. The analysis of the vibrational data is extended to the whole series of alkaline-earth iron and ruthenium hydrides A2TH6 (A=Mg, Ca, Sr; T=Fe, Ru) in order to identify correlations between selected frequencies and the TH bond length. The bulk moduli of Ca2FeH6 and Sr2RuH6 have also been determined within DFT. Their calculated values prove to compare well with the experimental values reported for Mg2FeH6 and several other compounds of this structure.
- Hagemann,Danna,Lawson Daku,Gomes,Renaudin,Yvon
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- X-ray and neutron powder diffraction study of the order-disorder transition in Eu2IrH5 and the mixed crystal compounds Eu2-xAxIrH5 (A = Ca, Sr; x = 1.0, 1.5)
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The title compounds and their deuterides have been prepared by solid-state and solid-gas reactions from the elements and investigated by X-ray and neutron powder diffraction as a function of temperature. At room temperature they crystallize with an anion-deficient cubic K2PtCl6-type structure (space group Fm3m) in which five hydrogen (deuterium) atoms surround iridium randomly on six octahedral sites with average bond distances of Ir-D=169-171pm. At low temperature they undergo a tetragonal deformation (space group I4/mmm) to the partially ordered Sr2IrD5 (T=4.2K)-type structure in which four hydrogen (deuterium) atoms occupy planar sites with full occupancy (Ir-D=166-170pm) and two hydrogen (deuterium) atoms axial sites (Ir-D=174-181pm) with ～50% occupancy, i.e., the data are consistent with a mixture of square-pyramidal [IrD5]4- complexes pointing in two opposite directions. The transitions occur at ～240K (Eu0.5Ca1.5IrD5, Eu0.5Sr1.5IrD5), ～210K (EuSrIrD5), ～200K (EuCaIrD5, Eu2IrD5), and are presumably of first order.
- Kohlmann,Moyer Jr.,Hansen,Yvon
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- The many phases of CaC2
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Polymorphic CaC2 was prepared by reacting mixtures of CaH2 and graphite with molar ratios between 1:1.8 and 1:2.2 at temperatures between 700 and 1400 °C under dynamic vacuum. These conditions provided a well controlled, homogeneous, chemical environment and afforded products with high purity. The products, which were characterized by powder X-ray diffraction, solid state NMR and Raman spectroscopy, represented mixtures of the three known polymorphs, tetragonal CaC2-I and monoclinic CaC2-II and -III. Their proportion is dependent on the nominal C/CaH2 ratio of the reaction mixture and temperature. Reactions with excess carbon produced a mixture virtually free from CaC2-I, whereas high temperatures (above 1100 °C) and C-deficiency favored the formation of CaC2-I. From first principles calculations it is shown that CaC2-I is dynamically unstable within the harmonic approximation. This indicates that existing CaC2-I is structurally/dynamically disordered and may possibly even occur as slightly carbon-deficient phase CaC2-δ. It is proposed that monoclinic II is the ground state of CaC2 and polymorph III is stable at temperatures above 200 °C. Tetragonal I represents a metastable, heterogeneous, phase of CaC2. It is argued that a complete understanding of the occurrence of three room temperature modifications of CaC2 will require a detailed characterization of compositional and structural heterogeneities within the high temperature form CaC2-IV, which is stable above 450 °C. The effect of high pressure on the stability of the monoclinic forms of CaC2 was studied in a diamond anvil cell using Raman spectroscopy. CaC2-II and -III transform into tetragonal CaC2-I at about 4 and 1GPa, respectively.
- Konar, Sumit,Nylén, Johanna,Svensson, Gunnar,Bernin, Diana,Edén, Mattias,Ruschewitz, Uwe,H?ussermann, Ulrich
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- Hydrogen impurity effects. A5Tt3 intermetallic compounds between A = Ca, Sr, Ba, Eu and Tt = Si, Ge, Sn with Cr5B3-like structures that are stable both as binary and as ternary hydride and fluoride phases
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All of the binary systems Ca, Sr, Ba, or Eu (A) with Tt (tetrel) = Si or Ge as well as Sr-Sn form both binary Cr5B3-type A5Tt3 phases and the corresponding ternary hydrides with stuffed Cr5B3- (Ca5Sn3F-) type structures. All of those tested, Ca-Si, Ba-Si, Ca-Ge, also yield the isotypic A5Tt3Fx phases. The tetragonal structures of Ca5Si3, Ca5Si3F0.42, Sr5Si3, Eu5Si3Hx, Ca5Ge3, Ca5Ge3Hx, Ca5Ge3F0.66(I4/mcm, No. 140) and of Ba5Si3F0.16 (P4/ncc, Ba5Si3-type) were refined from single-crystal X-ray diffraction data. The interstitial H, F atoms are bound in a constricted tetrahedral (A2+)4 cavity in the Cr5B3-type heavy atom structure, which can be described ideally as (A2+)5(Tt2)6-(Tt)4-. Many of 14 previous reports of the phases reported here were apparently hydrides according to lattice constant differences or, for Sr5Si3, the fractional coordinates of Sr2 about the tetrahedral site. An articulated model is developed that allows description of the relationship between the dimensions of the tetrahedral interstitial site and the cation cavity about Tt2 and for some matrix effects in this structure type. The model suggests limitations on the stability of these binary A5Tt3 compounds for the heavier tetrels, as observed. The resistivities of Ca5Ge3 and Ca5Ge3Hx are both characteristic of poor metals, and Pauli-like magnetic susceptibilities are exhibited by Ca5Ge3, Ca5Ge3Hx, Ca5Ge3F0.66, Sr5Ge3, and Sr5Sn3. The characteristic ideal Tt26- dimers are evidently not realistic descriptions for these phases; rather at least some of the η*4 electrons in the dimers are delocalized in a conduction band. This effect appears to be greater in two europium salts. Bond lengths of dimers in the Ca-Si and Ca-Ge families appear to shorten slightly in three instances of their oxidation to form the hydride or the fluoride, as might be expected.
- Leon-Escamilla,Corbett, John D.
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- Synthesis and characterization of a new ternary imide-Li 2Ca(NH)2
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The ternary imide Li2Ca(NH)2 was successfully synthesized by dehydrogenating a mixture of LiNH2 and CaH2 at a molar ratio of 2:1 in a stream of purified argon at 300°C. A powder X-ray diffraction measurement revealed that Li2Ca(NH)2 was of the trigonal anti-La2O3 structure (space group P3m1) with lattice constants of a = 3.5664(3)A and c = 5.9540(8) A. Ca occupied the 1b site (0, 0, 1/2), Li occupied the 2d site (1/3, 2/3, 0.8841(22)), and N occupied the 2d site (1/3, 2/3, 0.2565(15)). Nuclear magnetic resonance and X-ray absorption fine structure analyses demonstrated that each Li ion was coordinated with four imide ions and each Ca ion was coordinated with six imide ions.
- Wu, Guotao,Xiong, Zhitao,Liu, Tao,Liu, Yongfeng,Hu, Jianjiang,Chen, Ping,Feng, Yuanping,Wee, Andrew T. S.
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- Hydrogen storage of metal nitride by a mechanochemical reaction
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Metal imides (Li2NH, CaNH), a metal amide (LiNH2) and metal hydrides (LiH, CaH2) were synthesized by ball milling of their respective metal nitrides (Li3N, Ca3N2) in a H2 atmosphere at 1 MPa and at room temperature.
- Kojima, Yoshitsugu,Kawai, Yasuaki
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- Synthesis and Photoluminescence Properties of Rare-Earth-Activated Sr3- xAxAlO4H (A = Ca, Ba; x = 0, 1): New Members of Aluminate Oxyhydrides
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A series of aluminate-based oxyhydrides, Sr3-xAxAlO4H (A = Ca, Ba; x = 0, 1), has been synthesized by high-temperature reaction of oxide and hydride precursors under a H2 atmosphere. Their crystal structures determined via X-ray and neutron powder diffraction are isostructural with tetragonal Sr3AlO4F (space group I4/mcm), consisting of (Sr1-x/3Ax/3)2H layers and isolated AlO4 tetrahedra. Rietveld refinement based on the diffraction patterns and bond-valence-sum analysis show that Ba preferentially occupies the 10-coordinated Sr1 sites, while Ca strongly prefers to occupy the 8-coordinated Sr2 sites. Luminescence owing to the 4f-5d transition of Eu2+ or Ce3+ was observed from Eu- and Ce-doped samples, Sr3-x-yAxByAlO4H (A = Ca, Ba; B = Eu, Ce; x = 0, 1, y = 0.02), under excitation of near-ultraviolet light. Compared with its fluoride analogue, Sr3AlO4H:Ce3+ shows red shifts of both the excitation and emission bands, which is consistent with the reported hydride-based phosphors and can be explained by the covalency of the hydride ligands. The observed luminescence spectra can be decomposed into two sets of sub-bands corresponding to Ce3+ centers occupying Sr1 and Sr2 sites with distinctly different Stokes shifts (1.27 and 0.54 eV, respectively), as suggested by the results of constrained density functional theory (cDFT). The cDFT results also suggest that the large shift for Ce3+ at Sr1 is induced by large distortion of the coordinated structure with shortening of the H-Ce bond in the excited state. The current findings expand the class of oxyhydride materials and show the potential of hydride-based phosphors for optical applications.
- Fujii, Kotaro,Matsuishi, Satoru,Murakami, Taito,Wu, Tong,Yashima, Masatomo
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- High temperature hydrogenation of CaC6
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The structure and superconducting properties of high temperature hydrogenated calcium-graphite intercalation compound, CaC6 have been investigated using room temperature X-ray diffraction, and temperature and field dependence of magnetisation.
- Srinivas,Howard,Skipper,Bennington,Ellerby
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- Hydride and ammonia dispersion of metals
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Chemical (hydride and ammonia) dispergation of Group II-V metals induced by hydrogen and ammonia in the temperature range of 100-500°C at a pressure of 0.5-2.0 MPa was studied. The phase transitions in the M-H2 and M-NH3 systems were investigated and conditions for metal hydride and nitride formation as highly dispersed powders were identified. The characteristic features of metal dispergation under the action of hydrogen and ammonia and the degrees of dispersity of the obtained powders were compared.
- Fokin,Fokina,Tarasov
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- YHO, an Air-Stable Ionic Hydride
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Metal hydride oxides are an emerging field in solid-state research. While some lanthanide hydride oxides (LnHO) were known, YHO has only been found in thin films so far. Yttrium hydride oxide, YHO, can be synthesized as bulk samples by a reaction of Y2O3 with hydrides (YH3, CaH2), by a reaction of YH3 with CaO, or by a metathesis of YOF with LiH or NaH. X-ray and neutron powder diffraction reveal an anti-LiMgN type structure for YHO (Pnma, a = 7.5367(3) ?, b = 3.7578(2) ?, and c = 5.3249(3) ?) and YDO (Pnma, a = 7.5309(3) ?, b = 3.75349(13) ?, and c = 5.3192(2) ?); in other words, a distorted fluorite type with ordered hydride and oxide anions was observed. Bond lengths (average 2.267 ? (Y-O), 2.352 ? (Y-H), 2.363 ? (Y-D), >2.4 ? (H-H and D-D), >2.6 ? (H-O and D-O), and >2.8 ? (O-O)) and quantum-mechanical calculations on density functional theory level (band gap 2.8 eV) suggest yttrium hydride oxide to be a semiconductor and to have considerable ionic bonding character. Nonetheless, YHO exhibits a surprising stability in air. An in situ X-ray diffraction experiment shows that decomposition of YHO to Y2O3 starts at only above 500 K and is still not complete after 14 h of heating to a final temperature of 1000 K. YHO hydrolyzes in water very slowly. The inertness of YHO in air is very beneficial for its potential use as a functional material.
- Zapp, Nicolas,Auer, Henry,Kohlmann, Holger
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p. 14635 - 14641
(2019/11/03)
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- Phase diagram study of CaBr2-CaHBr system
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A study of binary, CaBr2-CaHBr system was carried out by differential thermal analysis (DTA), covering the composition range from 100 % CaBr2 to 100 % CaHBr between room temperature and 800 C. From DTA results, the contour of solidus
- Vishnu Vardhan, Chilakapati Venkata,Ghosh, Sajal,Nagaraj, Subramaniam,Sridharan, Raghavachary,Gnanasekaran, Thiagarajan
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p. 127 - 131
(2013/06/04)
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- Ca(BH4)2-LiBH4-MgH2: A novel ternary hydrogen storage system with superior long-term cycling performance
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A ternary hydrogen storage system, of superior cyclic stability and high capacity, was developed from a mixture of Ca(BH4)2, LiBH4 and MgH2 in molar ratios of 1:2:2. Investigation on both non-isothermal and isothermal hydrogen desorption/absorption properties shows that the hydrogen desorption starts from 320 °C and completes at 370 °C under a heating rate of 2 °C min-1, releasing ca. 8.1 wt% H2. The finishing temperature of desorption is much lower and the capacity much higher than any of the two-hydride mixtures in the ternary system. In particular, hydrogenation of the ternary system initiates at an extremely low temperature of ca. 75 °C and the onset dehydrogenation temperature is significantly reduced by 90 °C after the initial dehydrogenation/ hydrogenation cycle, which is ascribed to the formation of an active dual-cation hydride of CaMgH3.72 for dehydrogenation in the hydrogenation process. There is ca. 7.6 wt% H2 absorbed at 350 °C and 90 bar H2 for 18 h for the system post-dehydrogenated at 370 °C for 30 min, demonstrating a reversibility of over 94%. The capacity seems to fade mainly in the initial few cycles and stabilizes after further cycling. The reversibility is as high as 97% and a dehydrogenation capacity of ca. 6.2 wt% H2 at the 10th cycle. Favourable kinetics and thermodynamics of hydrogen desorption/absorption are achieved, which are responsible for the low completion temperature and the superior cycling performance. Mechanisms of the improved dehydrogenation/hydrogenation properties including the cyclic behaviour of the system are also proposed in relation to microstructural analyses.
- Gao, Mingxia,Gu, Jian,Pan, Hongge,Wang, Yiliu,Liu, Yongfeng,Liang, Chu,Guo, Zhengxiao
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p. 12285 - 12292
(2013/10/01)
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- Formation of impurity Si2OH6 in silane synthesized from silicon tetrafluoride
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The possibility of the reduction of hexafluorodisiloxane by calcium hydride in the synthesis of silane from silicon tetrafluoride has been studied. This reaction is shown to be not decisive for oxygen contamination of silane. The most likely reason for the appearance of impurity Si2OH6 in "fluoride" silane is the Ca(OH)2-catalyzed reaction of silane with trace water. The concentration of impurity Si2OH 6 in silane at the stage of synthesis may be efficiently decreased by the preliminary purging of calcium hydride with a hydrogen (grade A) flow.
- Bulanov,Sennikov,Sozin, A. Yu.,Lashkov, A. Yu.,Troshin, O. Yu.
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p. 510 - 512
(2011/07/29)
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- Synthesis of calcium alanate and its dehydriding performance enhanced by FeF3 doping
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Ca(AlH4)2 was synthesized by ball-milling the mixture of NaAlH4 and CaCl2 in a molar ratio of 2:1 and under a hydrogen atmosphere of 1 MPa. The results indicate that the reactants have entirely transformed to Ca(AlH4)2 with a byproduct of NaCl after ball-milling for 48 h. Investigations of dehydriding behavior of the as-prepared Ca(AlH4)2 sample show that approximately 5.2 wt.% of hydrogen is desorbed during the first two dehydrogenation reactions of Ca(AlH4)2, which exhibit an exothermic event at 148 °C and an endothermic event at 267 °C, respectively. The high temperature dehydrogenation at 267 °C mainly concentrates on the thermolysis of CaAlH5 intermediate. FeF3-doped Ca(AlH4) 2 system represents an improved dehydriding performance, the dehydrogenation temperature of CaAlH5 intermediate is decreased about 43 °C. After FeF3 doping, the apparent activation energy of CaAlH5 is reduced from 153.4 kJ/mol (undoped) to 88.3 kJ/mol (doped), it renders a possibility to realize the rehydrogenation of CaAlH5. The catalytic effect is attributed to a fluorine transfer reaction that occurred to generate CaF2 and Fe catalysts.
- Li, Changxu,Xiao, Xuezhang,Chen, Lixin,Jiang, Kun,Li, Shouquan,Wang, Qidong
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p. 590 - 595
(2011/02/23)
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- Improved dehydrogenation properties of Ca(BH4) 2-LiNH2 combined system
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Ca(BH4)2-LiNH2 combined system is shown to release hydrogen at much lower temperature compared to the pure Ca(BH 4)2. The improved dehydrogenation in this system can be ascribed to a combination reaction between [BH4] and [NH2] based on the reaction mechanism of positive H and negative H. The Royal Society of Chemistry 2010.
- Chu, Hailiang,Xiong, Zhitao,Wu, Guotao,Guo, Jianping,He, Teng,Chen, Ping
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p. 10585 - 10587
(2011/01/06)
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- Thermal decomposition behavior of calcium borohydride Ca(BH4)2
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The thermal decomposition behavior of adduct-free Ca(BH4)2, prepared by heating Ca(BH4)2·2THF powder under vacuum, was investigated by X-ray diffraction and thermal analyses. It has been found that Ca(BH4)2 undergoes a polymorphic transformation at 440 K and eventually decomposes in two steps between 620 and 770 K. CaH2 and an unknown intermediate compound form after the first step, but CaH2 is the only crystalline phase observed after the second step with a total weight loss of about 9.0 wt.%.
- Kim, Jae-Hun,Jin, Seon-Ah,Shim, Jae-Hyeok,Cho, Young Whan
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- On the preparation of calcium gallohydride
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The reaction of CsGaH4 or RbGaH4 with CaI2 in THF produced calcium gallohydride CaHGaH4 ? THF (I). DTA showed that compound I decomposes with an endotherm in the range 116-130°C. CaHGaH4 ? THF is well soluble in diglyme. In the IR spectrum of compound I, there is a strong band at 1780 cm-1, which is intrinsic to the Ga-H stretching vibrations.
- Bakum,Kuznetsova
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p. 849 - 849
(2009/02/01)
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- Calcium borohydride for hydrogen storage: Catalysis and reversibility
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We demonstrate a new solid-state synthesis route to prepare calcium borohydride, Ca(BH4)2 by reacting a ball-milled mixture of CaB6 and CaH2 in a molar ratio of 1:2 at 700 bar of H2 pressure and 400-440°C. Moreover, doping with catalysts was found to be crucial to enhance reaction kinetics. Thermogravimetric analysis and differential scanning calorimetry revealed a reversible low-temperature to high-temperature endothermic phase transition at 140°C and another endothermic phase transition at 350-390°C associated with hydrogen release upon formation of CaB6 and CaH2, as was evident from X-ray diffraction analysis. Thus, since Ca(BH4)2 here is shown to be prepared from its anticipated decomposition products, the conclusion is that it has potential to be utilized as a reversible hydrogen storage material. The theoretical reversible capacity was 9.6 wt % hydrogen.
- Roennebro, Ewa,Majzoub, Eric H.
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p. 12045 - 12047
(2008/10/09)
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- Polyanionic hydrides from polar intermetallics AeE2 (Ae = Ca, Sr, Ba; E = Al, Ga, In)
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The hydrogenation behavior of the polar intermetallic systems AeE 2 (Ae = Ca, Sr, Ba; E = Al, Ga, In) has been investigated systematically and afforded the new hydrides SrGa2H2 and BaGa2H2. The structure of these hydrides was characterized by X-ray powder diffraction and neutron diffraction of the corresponding deuterides. Both compounds are isostructural to previously discovered SrAI 2H2 (space group P3m1, Z = 1, SrGa2H 2/D2: a = 4.4010(4)74.3932(8) A, c = 4.7109(4)/4.699(1) A; BaGa2H2/D2: a = 4.5334(6)/4.5286(5) A, c = 4.9069(9)/4.8991(9) A). The three hydrides SrAI2H2, SrGa2H2, and BaGa2H2 decompose at around 300 °C at atmospheric pressure. First-principles electronic structure calculations reveal that H is unambiguously part of a two-dimensional polyanion [E2H 2]2- in which each E atom is tetrahedrally coordinated by three additional E atoms and H. The compounds AeE2H2 are classified as polyanionic hydrides. The peculiar feature of polyanionic hydrides is the incorporation of H in a polymeric anion where it acts as a terminating ligand. Polyanionic hydrides provide unprecedented arrangements with both E-E and E-H bonds. The hydrogenation of AeE2 to AeE2H 2 takes place at low reaction temperatures (around 200 °C), which suggests that the polyanion of the polar intermetallics ([E2] 2-) is employed as precursor.
- Bjoerling, Thomas,Noreus, Dag,Haeussermann, Ulrich
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p. 817 - 824
(2007/10/03)
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- Disproportionation of CaNi3 hydride: Formation of new hydride, CaNiH3
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The hydrogenation properties of CaNi3 were investigated at temperatures ranging from 298 to 773 K by differential thermal analysis (DTA). This compound exhibited four exothermic peaks at 373, 498, 543 and 653 K followed by an endothermic peak at 748 K when the compound was heated to 773 K under a hydrogen atmosphere of 3 MPa, and its final products were CaH2 and Ni. However, the formation of a new ternary hydride was observed in the X-ray diffraction (XRD) profiles below the endothermic reaction temperature at which the final products were formed. The Rietveld refinement of the obtained XRD profiles and a volumetric measurement of the hydrogen content based on the Sieverts' method indicated that this new phase was CaNiH3 with a cubic CsCl type structure for the metal constituents. The experimental data obtained by XRD and DTA were discussed from the viewpoint of the disproportionation of CaNi3 in the hydrogen atmosphere.
- Takeshita, Hiroyuki T.,Oishi, Toshio,Kuriyama, Nobuhiro
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p. 266 - 273
(2008/10/08)
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- Preparation and fine purification of SiF4 and 28SiH4
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Silicon tetrafluoride was obtained by the thermal decomposition of pure-grade sodium hexafluorosilicate and purified by low-temperature distillation. Next, SiF4 was 28Si-enriched by centrifugation and converted to silane by calcium h
- Bulanov,Balabanov,Pryakhin,Troshin
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p. 283 - 287
(2008/10/08)
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- Ba21Ge2O5H24 and Related Phases. A Corrected Structure Type and Composition for a Zintl Phase Stabilized by Hydrogen
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Syntheses of the so-called suboxide phases Ba21T2O5 (T = Ge, Si, Ga, In, Tl) are achieved only in the presence of hydrogen. The heavy-atom structure of Ba21Ge2O5H24 at room temperature was redetermined by single-crystal X-ray diffraction and found to be primitive trigonal symmetry (P3121 (No. 152), Z = 6, a = 14,4227(5) ?, c = 35.332(3) ?) instead of the previously refined cubic (Fd3?m) result. The change greatly improves the heavy-atom parameters. Twenty-four independent deuterium atoms have also been located by time-of-flight neutron diffraction, The structure contains Ba2+ cations, and three different types of monatomic anions. corresponding to the oxidation states (Ba+2)21(Ge-4)2(O-2) 5(H-)24. The deuterium atoms occupy tetrahedral, square-pyramidal, and octahedral barium interstices while the oxide anions lie in nearly regular octahedral barium polyhedra. The germanide anions are surrounded by 12 barium atoms in a distorted icosahedral configuration. Property measurements show that Ba21Ge2O5H24 is diamagnetic and is a semiconductor (or insulator). The analogues Ba21Tr2O5Hx, Tr = Ga, In, Tl, are isotypic with the heavy-atom structure of the title phase and presumably contain 22 hydride ions.
- Huang, Baoquan,Corbett, John D.
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p. 1892 - 1899
(2008/10/08)
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- Ca2RhH5.4 - Structure determination via neutron diffraction experiments
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The structure of Ca2RhH5 described by Moyer et al. is only known respective to the arrangement of the metal atoms. Elastic neutron diffraction experiments on the deuterated compound led to the complete structure, which corresponds to that of the K2PtCl6 type structure with the chloride sites statistically occupied in accordance with the formula of the mixed valent compound Ca2RhD5.4. A neutron diffraction diagram of a high resolution T-O-F spectrometer led to the up to now unknown compound Ca8Rh5D23 which crystallises isotypic to the analogous strontium compound in an atomic arrangement representing a transition from the K2PtCl6 type to the perovskite type structure.
- Bronger,Jansen,Breil
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p. 1477 - 1480
(2008/10/09)
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- Synthesis of Coarsely Crystalline Metal Hydrides
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Hydrogenation of metals with high-purity chemically active hydrogen under a pressure of 0.5-3.0 MPa was studied. Yttrium and lanthanum trihydrydes were prepared from compact metals at room temperature; titanium, zirconium, and vanadium dihydrides, from metal powders at room temperature; and calcium, strontium, and barium dihydrides, from compact metals at 150-200°C.
- Fokin,Fokina,Shilkin
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p. 1210 - 1212
(2007/10/03)
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- Synthesis, structure and thermal stability of Yb4Mg4Fe3H22
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Yb4Mg4Fe3H22 and its deuteride were prepared by sintering mixtures of YbMg, Fe and LiH (LiD) powders in the ratio YbMg:Fe:LiH (LiD) = 4:3:1 at 510-520 °C and 120-155 bar hydrogen (deuterium) pressure, and were characterized by X-ray and neutron powder diffraction. They crystallize with cubic symmetry (space group, P4/mmm; hydride, a = 6.6936(4) angstroms; deuteride, a = 6.6839(5) angstroms, and are isostructural with the calcium analogue Ca4Mg4Fe3H22. The deuteride contains octahedral [FeD6]4- complex anions with bond distances [Fe-4D1] = 1.586(5) angstroms and [Fe-2D2] = 1.554(7) angstroms, and tetrahedrally coordinated D- anions with bond distances [D3-Mg] = 1.915(9) angstroms and [D3-3Yb] = 2.411(7) angstroms. At a hydrogen pressure of 6 bar, the Yb compound decomposes at about 480 °C into YbH2, Mg and Fe, whereas the Ca analogue decomposes at about 450 °C into Ca2FeH6, Mg and Fe. The enthalpies of desorption, as measured from pressure-composition isotherms, are 137(3) kJ (mol H2)-1 for Yb4Mg4Fe3H22 and 122(4) kJ (mol H2)-1 for Ca4Mg4Fe3H22.
- Huang, B.,Yvon, K.,Fischer, K.
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