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New compounds with the general formula A x A"3-x B y B"1-y (A, A" = Li, Na; B, B" = Sb, Bi) were prepared in the system Li–Na–Sb–Bi. Na3Sb0.5Bi0.5has a hexagonal structure (Na3As type, a= 5.415 A, c= 9.595 A), and Li3Sb0.5Bi0.5and Li2NaSb0.5Bi0.5have a cubic structure (BiF3type, a= 6.645 and 6.772 A, respectively). The phase transitions of alkali-metal pnictides were studied by in situ x-ray diffraction at room temperature and pressures from 105Pa to 9.0 GPa. Li3Sb and Na3Sb were each shown to exist in two polymorphs with hexagonal (Na3As type) and cubic (BiF3type) structures. At atmospheric pressure, Li3Sb undergoes an irreversible α–β phase transition at 650°C, while Na3Sb undergoes a reversible transformation into a cubic phase at ≃2.3 GPa and room temperature. |
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