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7439-95-4Relevant articles and documents
The effect of H2 partial pressure on the reaction progression and reversibility of lithium-containing multicomponent destabilized hydrogen storage systems
Price, Tobias E. C.,Grant, David M.,Weston, David,Hansen, Thomas,Arnbjerg, Lene M.,Ravnsbaek, Dorthe B.,Jensen, Torben R.,Walker, Gavin S.
, p. 13534 - 13538 (2011)
It is known that the reaction path for the decomposition of LiBH 4:MgH2 systems is dependent on whether decomposition is performed under vacuum or under a hydrogen pressure (typically 1-5 bar). However, the sensitivity of this multicomponent hydride system to partial pressures of H2 has not been investigated previously. A combination of in situ powder neutron and X-ray diffraction (deuterides were used for the neutron experiments) have shed light on the effect of low partial pressures of hydrogen on the decomposition of these materials. Different partial pressures have been achieved through the use of different vacuum systems. It was found that all the samples decomposed to form Li-Mg alloys regardless of the vacuum system used or sample stoichiometry of the multicomponent system. However, upon cooling the reaction products, the alloys showed phase instability in all but the highest efficiency pumps (i.e., lowest base pressures), with the alloys reacting to form LiH and Mg. This work has significant impact on the investigation of Li-containing multicomponent systems and the reproducibility of results if different dynamic vacuum conditions are used, as this affects the apparent amount of hydrogen evolved (as determined by ex situ experiments). These results have also helped to explain differences in the reported reversibility of the systems, with Li-rich samples forming a passivating hydride layer, hindering further hydrogenation.
Formation of one-dimensional MgH2 nano-structures by hydrogen induced disproportionation
Zlotea, Claudia,Lu, Jun,Andersson, Yvonne
, p. 357 - 362 (2006)
Remarkable formation of one-dimensional single crystalline MgH2 structures in the nano- and micro-meters ranges is reported. These structures have been tailored by hydrogen absorption and subsequent disproportionation of bulk Mg24Y5. The MgH2 whiskers have been structurally and morphologically characterized by X-rays diffraction, scanning and transmission electron microcopies. A growth model is proposed for the early stage of the whiskers formation by combining surface chemical and morphological investigations. The formation of MgH2 whiskers opens new engineering explorations and challenges for further experimental and theoretical studies.
Electrodeposition of aluminum, aluminum/magnesium alloys, and magnesium from organometallic electrolytes
Mayer
, p. 2806 - 2809 (1990)
In a previous publication we reported the evaluation of the organometallic aluminum electrolytes for electroforming applications. The electroformed deposits were of high purity and therefore exhibited a relatively low ultimate tensile strength of 65.5 MPa
Decomposition and oxidation of magnesium diboride
Guo, Yang,Zhang, Wei,Yang, Dong,Yao, Ru-Liang
, p. 754 - 759 (2012)
The decomposition and oxidation behavior of magnesium diboride (MgB 2) have been studied using thermogravimetry (TG), XRD and SEM-EDS. The reactions were carried out by heating MgB2powder in a stream of argon or air at atmospheric pressure. In the temperature range explored (298-1673 K), four successive steps were observed in the decomposition process of MgB2. The rate-limiting steps of the decomposition process were found to be associated with the nucleation or formation of boron-rich phases. The oxidation process of MgB2comprised five successive phases in the temperature range explored (298-1673 K). There was close relationship between the decomposition and oxidation behavior of MgB2. Experimental results showed that the decomposition reactions occurred during the oxidation process. The acceleration shown in the weight gain curve can be ascribed to the rapid oxidation of Mg vapor released from the decomposition reactions. The microstructure and composition of the oxide scale formed in the oxidation process were investigated using XRD and SEM-EDS. The oxide layer structure was identified based on the experimental results in this study.
Thermoelectric properties and microstructure of Mg3Sb2
Condron, Cathie L.,Kauzlarich, Susan M.,Gascoin, Franck,Snyder, G. Jeffrey
, p. 2252 - 2257 (2006)
Mg3Sb2 has been prepared by direct reaction of the elements. Powder X-ray diffraction, thermal gravimetric, differential scanning calorimetery, and microprobe data were obtained on hot pressed samples. Single phase samples of Mg
Crystal structure of κ-Ag2Mg5
Castro, Facundo J.,Primo, Gastón A.,Urretavizcaya, Guillermina
, p. 243 - 246 (2018)
The structure of κ-Ag2Mg5 has been refined based on X-ray powder diffraction measurements (Rwp = 0.083). The compound has been prepared by combining mechanical alloying techniques and thermal treatments. The intermetallic presents the prototypical structure of Co2Al5, an hexagonal crystal with the symmetries of space group P63/mmc, and belongs to the family of kappa-phase structure compounds. The unit cell dimensions are a=8.630(1) ? and c=8.914(1) ?. Five crystallographically independent sites are occupied, Wyckoff positions 12k, 6h and 2a are filled with Mg, another 6h site is occupied with Ag, and the 2c site presents mixed Ag/Mg occupancy. The crystal chemistry of the structure and bonding are briefly discussed in the paper.
Size-dependent hydrogen storage properties of Mg nanocrystals prepared from solution
Norberg, Nick S.,Arthur, Timothy S.,Fredrick, Sarah J.,Prieto, Amy L.
, p. 10679 - 10681 (2011)
Mg nanocrystals of controllable sizes were prepared in gram quantities by chemical reduction of magnesocene using a reducing solution of potassium with an aromatic hydrocarbon (either biphenyl, phenanthrene, or naphthalene). The hydrogen sorption kinetics were shown to be dramatically faster for nanocrystals with smaller diameters, although the activation energies calculated for hydrogen absorption (115-122 kJ/mol) and desorption (126-160 kJ/mol) were within previously measured values for bulk Mg. This large rate enhancement cannot be explained by the decrease in particle size alone but is likely due to an increase in the defect density present in smaller nanocrystals.
Hydrogen storage properties of Mg[BH4]2
Matsunaga,Buchter,Mauron,Bielman,Nakamori,Orimo,Ohba,Miwa,Towata,Züttel
, p. 583 - 588 (2008)
Among the large variety of possible complex hydrides only few exhibit a large gravimetric hydrogen density and stability around 40 kJ mol-1H2. Mg[BH4]2 is based on theoretical approaches a complex hydride with an equilibrium hydrogen pressure of approximately 1 bar at room temperature and a hydrogen content of 14.9 mass%. The reaction of Li[BH4] with MgCl2 at elevated temperatures was investigated as a possible route to synthesize Mg[BH4]2. Li[BH4] reacts with MgCl2 at a temperature >523 K at a pressure of 10 MPa of hydrogen, where the product contains LiCl and Mg[BH4]2. The desorption pc-isotherm of the product obtained at 623 K shows two flat plateaus, which indicates that the decomposition of the product consists of a two-step reaction. The products of the first and the second decomposition reaction were analyzed by means of X-ray diffraction and found to be MgH2 and Mg, respectively. The enthalpy for the first decomposition reaction was determined to be ΔH = -39.3 kJ mol-1H2 by the Van't Hoff plot of the equilibrium measurements between 563 K and 623 K, which is significantly lower than that for pure Li[BH4] (ΔH = -74.9 kJ mol-1H2). However, only the second reaction step (MgH2 → Mg) is reversible at the condition up to 623 K at 10 MPa of hydrogen.
Direct synthesis of Mg2FeH6 by mechanical alloying
Huot,Boily,Akiba,Schulz
, p. 306 - 309 (1998)
The hydride Mg2FeH6 was synthesized by high-energy ball milling of MgH2 and Fe under argon atmosphere without subsequent sintering. After 60 h of milling, 56% wt. of Mg2FeH6 was synthesized. This yiel
Enhancement of critical current density by a “MgB2-MgB4” reversible reaction in self-sintered ex-situ MgB2bulks
Peng, Junming,Cai, Qi,Cheng, Fang,Ma, Zongqing,Li, Chong,Xin, Ying,Liu, Yongchang
, p. 24 - 29 (2017)
Self-sintered ex-situ MgB2polycrystalline bulks have experienced a two-step sintering process, initially at 900?°C for 0–20?min and then at 650?°C for 1?h. MgB2was decomposed to MgB4and Mg at 900?°C and composed again at 650?°C from MgB4and Mg. The reversible reaction promotes the material migration, and thus eliminates pores and enhances the connectivity between the grains. The critical current density (Jc) is significantly improved due to both improved grain connectivity and the additive pinning centers such as MgB4and new-born boundaries. This two-step sintering process can be a promising method to fabricate high-performance ex-situ MgB2bulks and wires.
Hydride stability and hydrogen desorption characteristics in melt-spun and nanocrystallized Mg-Ni-La alloy
Tanaka, Kazuhide
, p. 432 - 439 (2008)
The hydrogen desorption properties of Mg-rich alloys are significantly improved by nanostructure formation. This effect is examined for a melt-spun and nanocrystallized Mg-Ni-La alloy by pressure-composition isotherm (PCT) and thermal desorption spectrum (TDS) measurements. This alloy exhibits fast desorption kinetics and favorable PCT characteristics with an H-capacity of ～4.6 wt%. TDS measurements reveal a definite peak ascribable to release of hydrogen from nanoboundaries, in addition to those associated with decompositions of hydrides such as MgH2, Mg2NiH4 and LaH3. Hydrogen transport along the nanoboundaries appears to facilitate the desorption kinetics in this alloy.
Hydrogenation Properties of Laves Phases LnMg2 (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Ho, Er, Tm, Yb)
Werwein, Anton,Maa?, Florian,Dorsch, Leonhard Y.,Janka, Oliver,P?ttgen, Rainer,Hansen, Thomas C.,Kimpton, Justin,Kohlmann, Holger
, p. 15006 - 15014 (2017)
The hydrogenation properties of Laves phases LnMg2 (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Ho, Er, Tm, Yb) were investigated by thermal analysis, X-ray, synchrotron, and neutron powder diffraction. At 14.0 MPa hydrogen gas pressure and 393 K, PrMg2 and NdMg2 take up hydrogen and form the colorless, ternary hydrides PrMg2H7 (P41212, a = 632.386(6) pm, c = 945.722(11) pm) and NdMg2H7 (P41212, a = 630.354(9) pm, c = 943.018(16) pm). The crystal structures were refined by the Rietveld method from neutron powder diffraction data on the deuterides (PrMg2D7, P41212, a = 630.56(2) pm, c = 943.27(3) pm; NdMg2D7, P41212, a = 628.15(2) pm, c = 940.32(3) pm) and shown to be isotypic to LaMg2D7. The LaMg2D7 type of hydrides decompose at 695 K (La), 684 K (Ce), 684 K (Pr), 672 K (Nd), and 639 K (Sm) to lanthanide hydrides and magnesium. The Laves phase EuMg2 forms a hydride EuMg2Hx of black color. Its crystal structure (P212121, a = 664.887(4) pm, b = 1136.993(7) pm, c = 1069.887(7) pm) is closely related to the hexagonal Laves phase (MgZn2 type) of the hydrogen-free parent intermetallic. GdMg2 and TbMg2 form hydrides GdMg2Hx with orthorhombic unit cells (a = 1282.7(4) pm, b = 572.5(2) pm, c = 881.7(2) pm) and TbMg2Hx (a = 617.8(3) pm, b = 1045.8(8) pm, c = 997.1(5) pm), presumably also with a distorted MgZn2 type of structure. CeMg2H7 and NdMg2H7 are paramagnetic with effective magnetic moments of 2.49(1) μB and 3.62(1) μB, respectively, in good agreement with the calculated magnetic moments of the free trivalent rare-earth cations (μcalc(Ce3+) = 2.54 μB; μcalc(Nd3+) = 3.62 μB).
Hydrogen cycling of niobium and vanadium catalyzed nanostructured magnesium
Schimmel, H. Gijs,Huot, Jacques,Chapon, Laurent C.,Tichelaar, Frans D.,Mulder, Fokko M.
, p. 14348 - 14354 (2005)
The reaction of hydrogen gas with magnesium metal, which is important for hydrogen storage purposes, is enhanced significantly by the addition of catalysts such as Nb and V and by using nanostructured powders. In situ neutron diffraction on MgNb0.05 and MgV0.05 powders give a detailed insight on the magnesium and catalyst phases that exist during the various stages of hydrogen cycling. During the early stage of hydriding (and deuteriding), a MgH1 phase is observed, which does not occur in bulk MgH2 and, thus, appears characteristic for the small particles. The abundant H vacancies will cause this phase to have a much larger hydrogen diffusion coefficient, partly explaining the enhanced kinetics of nanostructured magnesium. It is shown that under relevant experimental conditions, the niobium catalyst is present as NbH1. Second, a hitherto unknown Mg-Nb perovskite phase could be identified that has to result from mechanical alloying of Nb and the MgO layer of the particles. Vanadium is not visible in the diffraction patterns, but electron micrographs show that the V particle size becomes very small, 2-20 nm. Nanostructuring and catalyzing the Mg enhance the adsorption speed that much that now temperature variations effectively limit the absorption speed and not, as for bulk, the slow kinetics through bulk MgH2 layers.
The catalytic effect of Nb2O5 on the electrochemical hydrogenation of nanocrystalline magnesium
Zander,Lyubenova,K?ster,Dornheim,Aguey-Zinsou,Klassen
, p. 298 - 301 (2006)
Nanocrystalline Mg powder without and with 2 mol% Nb2O 5 catalyst was studied in a 6 M KOH electrolyte as electrode material for electrochemical hydrogen charging processes. Since the hydrogen overpotential of Mg, which is a measure of the hydrogen evolution at the electrode surface, was observed to be reduced by the addition of Nb 2O5, it is assumed that the catalyst influences the electrode reactions. Considering this assumption hydrogenation was studied at different current densities. The storage capacity as well as the kinetic of Mg/Nb2O5 electrodes increased significantly up to 1 wt.% H2 at a charging time of 30 min with decreasing current density. The storage capacity of nanocrystalline Mg powder showed only minor changes to lower hydrogen contents with decreasing current density.
Catalytic reduction of magnesia by carbon
Rongt, Li,Wei, Pan,Sano, Masamichi,Li, Jianqiang
, p. 265 - 267 (2003)
Reduction kinetics of magnesia with carbon and transition metal was investigated by thermogravimetry from room temperature to 1973 K. Cu, Co and Ni accelerates the reduction rate. Fe accelerates the reduction rate and decreases the initial reaction temper
The vibration-rotation emission spectrum of MgH2
Shayesteh,Appadoo,Gordon,Bernath
, p. 7785 - 7788 (2003)
The gaseous MgH2 molecule was discovered in an electrical discharge inside a furnace. The vibration-rotation emission spectrum of MgH 2 was recorded with a Fourier transform spectrometer. Three hot bands were found and rotationally analyzed. The MgH2 molecule was found to have a linear structure.
An electrochemical and XRD study of lithium insertion into mechanically alloyed magnesium stannide
Roberts,Cairns,Reimer
, p. A912-A916 (2003)
The intermetallic Mg2Sn is a promising negative electrode material for rechargeable lithium cells. Preliminary cycling tests have demonstrated stable capacities at 400 mAh/g for 20 cycles. Magnesium stannide was produced by mechanically alloying magnesium and tin powders. Mechanical alloying can convert the equilibrium Mg2Sn phase to a metastable phase by the introduction of defects with extended milling times. In situ X-ray diffraction has shown that the cubic Li2MgSn phase, which is similar in size and structure to cubic Mg2Sn, is produced by lithium insertion into the equilibrium and metastable phases. The conversion from the metastable phase is irreversible, so subsequent lithium removal from Li2MgSn produces the equilibrium Mg2Sn phase.
Reversible storage of hydrogen in destabilized LiBH4
Vajo, John J.,Skeith, Sky L.,Mertens, Florian
, p. 3719 - 3722 (2005)
Destabilization of LiBH4 for reversible hydrogen storage has been studied using MgH2 as a destabilizing additive. Mechanically milled mixtures of LiBH4 + 1/2MgH2 or LiH + 1/2MgB 2 including 2-3 mol % TiCl3 are shown to reversibly store 8-10 wt % hydrogen. Variation of the equilibrium pressure obtained from isotherms measured at 315-400?°C indicate that addition of MgH2 lowers the hydrogenation/dehydrogenation enthalpy by 25 kJ/(mol of H 2) compared with pure LiBH4. Formation of MgB2 upon dehydrogenation stabilizes the dehydrogenated state and, thereby, destabilizes the LiBH4. Extrapolation of the isotherm data yields a predicted equilibrium pressure of 1 bar at approximately 225?°C. However, the kinetics were too slow for direct measurements at these temperatures. ? 2005 American Chemical Society.
Photochemical Synthesis of Magnesium Dihydride and Methyl Magnesium Hydride in Cryogenic Matrices
McCaffrey, John G.,Parnis, J. Mark,Ozin, Geoffrey A.,Breckenridge, W. H.
, p. 4945 - 4950 (1985)
Photolysis at the 3p1P 1S resonance transition of magnesium atoms isolated in hydrogen-containing rare gas matrices is found to give rise to the first observed example of a group 2 metal atom dihydride, magnesium dihydride (MgH2), with no evidence for the fragmented products, MgH + H.Isotopic substitution studies in the infrared indicate that the molecule is linear as predicted by simple Walsh type MO diagrams and ab initio calculations.This is in contrast with gas-phase studies, where only fragments are observed.Possible reasons for the differing reaction behavior (i.e. in the matrix and gas phase) are discussed in terms of the matrix cage effect and differences between the vibrational relaxation rates in the condensed phase and those in the gas phase.Similar photochemical behavior is exhibited by magnesium atoms in neat methane matrices, where the linear inserted product, methyl magnesium hydride (CH3MgH), is formed as shown by infrared isotopic substitution experiments.No electronic absorptions were observed for either products in the range 230-800 nm.Emission is observed during magnesium atom photolysis in xenon and methane matrices.The bands present in the former matrix are assigned to singlet (3p1P -> 3s1S) and triplet (3p3P -> 3s1S) atomic magnesium emission, while the possible origins of the long-lived visible emission in the latter matrix are proposed.The presence of hydrogen in a xenon matrix (1:10 H2:RG) causes a decrease in the emission intensity relative to a neat xenon matrix but adds no additional features.The observation of only linear inserted products (MgH2 and CH3MgH) is interpreted in the context of a concerted insertion mechanism with no detectable contribution from an abstraction pathway.
Morphology and preferred orientation of pulse electrodeposited magnesium
Gummow, Rosalind J.,He, Yinghe
, p. E45-E49 (2010)
A nanocrystalline magnesium material with a high specific surface area is expected to react rapidly and reversibly with hydrogen gas to yield magnesium hydride, a hydrogen storage medium. In this paper, the feasibility of the synthesis of magnesium materials for hydrogen storage applications by pulse electrodeposition of magnesium from ethereal electrolytes containing Grignard reagents was investigated. Deposition onto flat stainless steel electrodes established that, as in dc deposition, the morphology of the deposits varied widely with electrolyte composition and charge density. Irregular, nanocrystalline magnesium films were formed at low current density (0.4 mA cm-2) and low charge density (1 C cm-2) using butylmagnesium chloride electrolytes in dibutyl diglyme, while at a higher current density (15 mA cm-2) in tetrahydrofuran, dense films were favored.
Low-temperature hydrogenation of Mg-Ni-Nb2O5 alloy processed by high-pressure torsion
Caba?as-Moreno, J. G.,Cruz-Gandarilla, F.,Hernández-Silva, O.,Herrera-Ramírez, M.,Osorio-García, M.,Suárez-Alcántara, K.,Tejeda-Ochoa, A.,Todaka, Y.
, (2021)
Powder mixtures with a nominal composition Mg-5 wt%Ni-2 wt%Nb2O5 are used to produce ultrafine-grained bulk material by high-pressure torsion (HPT) processing. Samples subjected to 10 and 20 revolutions in torsion under a pressure of 3 GPa developed an ultrafine grain size, mainly in the 100?200 nm range. The hydrogenation properties of these HPT-processed materials have been characterized at temperatures in the interval of 373–723 K. The hydrogenation experiments clearly show faster kinetics of hydrogenation and higher storage capacities in the HPT materials compared to the initial mild-milled powder mixture. The storage capacities have been limited to about 5.5 wt% H2 by the formation of a substantial amount of MgO in the materials after several hydrogenation cycles. However, as a matter of practical relevance, the production of bulk pieces of the Mg-Ni-Nb2O5 alloy having an ultrafine grain structure allows handling of the material without special precautions against ignition, as well as its storage in contact with air for several months with no evident deterioration of its fast activation in posterior hydrogenation treatments.
Phase Relationship of Mg2Si at High Pressures and High Temperatures and Thermoelectric Properties of Mg9Si5
Imai, Motoharu,Ibuka, Soshi,Isoda, Yukihiro
, p. 11394 - 11400 (2021)
Magnesium silicide (Mg2Si) is a promising eco-friendly thermoelectric material, which has been extensively studied in recent times. However, its phase behavior at high pressures and temperatures remains unclear. To this end, in this study, in situ X-ray diffraction analysis was conducted at high pressures ranging from 0 to 11.3 GPa and high temperatures ranging from 296 to 1524 K, followed by quenching. The antifluorite-phase Mg2Si decomposed to Mg9Si5 and Mg at pressures above 3 GPa and temperatures above 970 K. The antifluorite-phase Mg2Si underwent a structural phase transition to yield a high-pressure room-temperature (HPRT) phase at pressures above 10.5 GPa and at room temperature. This HPRT phase also decomposed to Mg9Si5 and Mg when heated at ～11 GPa. When 5Mg2Si decomposed to Mg9Si5 and Mg, the volume reduced by ～6%. Mg9Si5 synthesized at high pressures and high temperatures was quenchable under ambient conditions. Thermoelectric property measurements of Mg9Si5 at temperatures ranging from 10 to 390 K revealed that it was a p-type semiconductor having a dimensionless thermoelectric figure of merit (ZT) of 3.4 × 10-4 at 283 K.
Direct synthesis of Mg-Ni compounds from their oxides
Tan, Serdar,Aydinol, Kadri,?ztürk, Tayfur,Karakaya, Shak
, p. 134 - 140 (2010)
A study was carried out on the synthesis of Mg-Ni compounds as well as on the extraction of pure Ni and Mg from their oxides using the method of electro-deoxidation. The oxides sintered at 1200 °C were in the form of discrete phases NiO and MgO, suitably proportioned to yield Ni, MgNi 2, Mg2Ni and Mg. The oxides were electrolyzed at 3.2 V in a eutectic mixture of CaCl2-NaCl solution maintained at a constant temperature (900-600 °C), using a graphite anode. The study has shown that NiO rich mixture, MgO:NiO = 1:2, can be reduced successfully to metallic state. Some loss of Mg was apparent in the latter, with the result that the product was far from the target composition MgNi2. The electroreduction of MgO rich mixtures was difficult to achieve. The mixture MgO:NiO = 2:1 when electrolyzed at 725 °C for 24 h, could be reduced to metallic phases only in small proportions (18 wt.%). In pure MgO, no trace of reduction was observed during the electrolysis at 600 °C. Difficulties in the electroreduction of MgO and MgO rich mixtures were partially attributed to low conductivity of MgO.
High-pressure synthesis of novel hydrides in Mg-RE-H systems (RE = Y, La, Ce, Pr, Sm, Gd, Tb, Dy)
Kamegawa,Goto,Kakuta,Takamura,Okada
, p. 284 - 287 (2006)
The high-pressure synthesis of new hydrides of Mg-RE-H systems, where RE = Y, La, Ce, Pr, Sm, Gd, Tb and Dy, were conducted by using a cubic-anvil-type apparatus, and their crystal structure, thermal stabilities and hydrogen contents were investigated. In Mg-Y-H system, newly found MgY2H y with a FCC-type structure has been prepared. In MgH2-x mol% REH (REH = LaH3, CeH2.5 and PrH3), new hydrides with primitive tetragonal structure were synthesized around x = 25-33 under GPa-order high pressures. The lattice constants were a = 0.8193 nm, c = 0.5028 nm, a = 0.8118 nm, c = 0.4979 nm and a = 0.8058 nm, c = 0.4970 nm at x = 25 in Mg-La, Ce and Pr systems, respectively. The hydrogen contents of the novel compounds were 4.1, 3.7 and 3.9 mass% in Mg-La, Ce and Pr systems, respectively, and the chemical formulae were found to correspond to Mg 3LaH9, Mg3CeH8.1 and Mg 3PrH9. The new hydrides decomposed into Mg and rare-earth hydride at about 600 K (Mg3LaH9: 614 K, Mg 3CeH8.1: 609 K, Mg3PrH9: 630 K) with an endothermic reaction. In MgH2-x mol% hREH (hREH = GdH 3, TbH3 and DyH3), new hydrides with FCC-type structure were synthesized around x = 67.