超高圧下におけるAX_2,ABX_3およびA_2BX_4型酸化物およびカルコゲン化物の相転移とその結晶多形の構造
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The thermal equilibria at very high pressure were studied on the materials of disulfides and diselenides of germanium, metaoxogermanates and silicates of strontium and barium, and orthothiogermanates and thiosilicate of manganese and magnesium. Several new high pressure -polymorphisms were found. Tetragonal GeS_2III of isostructure with HgI_2 (red) was equilibrated at about 75 kbar/600℃, tetragonal GeSe_2II of isostructure with GeS_2II equilibrated at 60 kbar/600℃. Pseudoorthorohmbic SrGeO_3II, BaGeO_3II and SrSiO_3II like the high temperature phase of BaGeO_3 were equilibrated at 10 kbar, 30 kbar and 34 kbar, respectively. Cubic perovskite SrGeO_3III was stabilized at about 50 kbar. Both hexagonal 9H-type and 4H-type-like perovskite-like BaGeO_3 were stabilized at about 95 kbar. It was found that Mn_2GeS_4, Mn_2SiS_4 and Mg_2GeS_4 having the olivine type structure were decomposed into the momo and disulfides of the constituent metals under the high pressure ranging 70 to 85 kbar. The large volume change amounting to 37 percents or so was observed when tne coordination number of cations increased at the phase transition. The volume change without change of coordination number was generally below ten percents. The lattice constants of these new polymorphisms were as follows; a=3.469(1)Å, c=10.978(1)Å for the tetragonal GeS_2III, a=5.731(4)Å, c=9.702(7)Å for the tetragonal GeSe_2II, a=8.652(2)Å, b=11.136(3)Å, c=37.20(1)Å for the pseudoorthorohmbic SrGeO_3II, a=3.7964(3)Å for the cubic SrGeO_3III, a=9.011(6)Å, b=11.580(6)Å, c=38.84(1)Å for the pseudoorthorohmbic BaGeO_3II, a=5.648(4)Å, c=21.07(10)Å, and a=5.603(1)Å, c=9.11(1)Å for hexagonal 9H-type and 4H-type-like BaGeO_3, respectively, and a=8.492(6)Å, b=10.913(7)Å, c=36.25(2)Å for the pseudoorthorohmbic SrSiO_3II.
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