Phase formation and electrical properties of Bi2O3-based compounds in the Bi2O3-La2O3-MoO3 system

The ternary system Bi2O3-La2O3-MoO3 is shown to contain a wide range of (Bi2O3)(x)(La2O3)(y)(MoO3)(z) (x + y + z = 1) compounds isostructural with the cubic phase 8-81203, stable at room temperature: 0.65 <= x <= 0.93. In addition, the ternary system contains two tetragonal phases (3 at x = 0.96 and f3' in the region 0.50 <= x <= 0.61, 0.14 <= y <= 021, and 0.22 <= z <= 0.31) and a rhombohedral phase in a narrow composition range (0.60 <= x <= 0.64) on the Bi2O3-La2MoO6 join. When heated to 1000-1100 C, the rhombohedral and 13, tetragonal compounds undergo one phase transition, to the cubic phase with the delta-Bi2O3 structure. The samples with the delta-Bi2O3 structure exhibit a more complex polymorphism. The electrical conductivity of the samples increases with Bi2O3 concentration. The conductivity of the cubic materials with x = 0.8 reaches 0.6 S/cm at 800 degrees C. The high temperature (350-800 degrees C) conductivity of such samples follows the Vogel-Fulcher-Tammann law. At lower temperatures, their conductivity exhibits Arrhenius behavior with an activation energy near 0.8 eV. (C) 2016 Elsevier B.V. All rights reserved.