BaO-BiO_(1.5) Phase Diagram in the Region 80-100 mol percent BiO_(1.5) at p_(o_2) = 21 kPa

摘要

The phase equilibria in the region from 80 to 100 mol percent BiO_(1.5) are studied in the BaO-BiO_(1.5) system in air and under an argon atmosphere using visual polythermal analysis (VPA), X-ray powder diffraction, differential thermal analysis (DTA), electron diffraction (ED), and elemental analysis in a transmission electron microscope (EA TEM). A series of discrete layered rhombohedral phases (RPs) with the composition Ba_2Bi_(8+n)O_y, where n = 0, 1, 2, 4, 8, or 10, is discovered. The melting character is determined for these RPs: the 1 : 4 phase melts congruently; the 2 : 9, 1 : 5, 1 : 6, and 1 : 8 phases melt incongruently. The crystallization fields are 10-30 deg C. At p_(O_2) = 21 kPa, the 1 : 4 phase in the subsolidus region decomposes into a 4 : 13 perovs-kite-like phase and the 2 : 9 phase. The other rhombohedral phases decompose into stages to yield Bi_2O_3 and a neighboring RP that is richer in barium. The Ba_2Bi_(8+n)O_y oxides are stable in argon and experience a first-order phase transformation at about 560 deg C.