Synthesis of new compounds of the pseudo-ternary system SrO-Bi₂O₃-TeO₂ in air

Abstract

The phase equilibria of the pseudo-ternary system SrO-Bi₂O₃-TeO₂ at 600‡ to 850‡ C were examined in air by solid-state reaction techniques and X-ray powder diffraction. Three pseudo-ternary compounds were found: a hexagonal solid solution Bi₂O₃ · 2xSrO · 5xTeO₂ (x = 0.02 to 0.20,a = 0.394(1) to 0.399(5),c = 1.89(6) to 1.86(7) nm), a rhombohedral phase Bi₄Sr₃Te₅O₁₉ (a = 0.405(2),c = 2.71 (5) nm in hexagonal terms) and a cubic phase Bi₂SrTeO₇ (a = 1.086(9) nm). The Mössbauer spectra of¹²⁵Te in the compounds indicated that the tellurium atoms were mostly in the state of Te⁺⁴ in the former two compounds but were exclusively Te⁺⁶ in Bi₂SrTeO₇. The electrical conductivity of the first two were about 10⁻²Ω⁻¹ cm⁻¹ at 600‡ C. However, Bi₂SrTeO₇ was an electrical insulator.