OXYGEN-DEFICIENT AND ORDERED PEROVSKITE-TYPE SOLID-SOLUTION SYSTEM BA1+XBI1-XOY (0 LESS-THAN-OR-EQUAL-TO X LESS-THAN-OR-EQUAL-TO 0.5, 3.00 GREATER-THAN-OR-EQUAL-TO Y GREATER-THAN-OR-EQUAL-TO 2.75)

A new oxygen-deficient and ordered perovskite-type solid-solution system Ba1+xBi1-xOy(0 less-than-or-equal-to x less-than-or-equal-to 0.5, 3.00 greater-than-or-equal-to y greater-than-or-equal-to 2.75) was synthesized, with the estimated ionic configuration Ba(Ba2+xBi3+3.5-1.5x-yBi5+-3+0.5x+y)(Bi5+0.5)Oy. The lattice parameters and mean valence of bismuth in the sample annealed in one atmosphere of oxygen at 673 K were determined by powder X-ray diffraction and iodometric titration, respectively. Samples with the compositions 0 less-than-or-equal-to x less-than-or-equal-to 0.05, 0.10 less-than-or-equal-to y less-than-or-equal-to 0.15, 0.20 less-than-or-equal-to x less-than-or-equal-to 0.425, 0.45 less-than-or-equal-to x less-than-or-equal-to 0.475, and 0.475 less-than-or-equal-to x less-than-or-equal-to 0.50 were found to be monoclinic, rhombohedral, cubic, tetragonal and cubic, respectively. Oxygen deficiency was observed in the whole range of composition; the ordering of the oxygen vacancics was confirmed for x greater-than-or-equal-to 0.45. Oxygen deficiency at high temperatures was measured by P(O2)-controlled thermogravimetry for samples with the compositions, x = 0.33 and 0.50 and within the ranges of 873 less-than-or-equal-to T less-than-or-equal-to 1313 K and 0.001 less-than-or-equal-to P(O2) less-than-or-equal-to 1 atm. At least four phases were recognized in the phase diagram for the sample x = 0.33 in the measured range of the temperature and oxygen partial pressure, while no phase change was observed for the sample x = 0.50.