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 δ-Bi2O3, stable at room temperature: 0.65 ≤ x ≤ 0.93. In addition, the ternary system contains two tetragonal phases (β at x = 0.96 and β′ in the region 0.50 ≤ x ≤ 0.61, 0.14 ≤ y ≤ 0.21, 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 β′ tetragonal compounds undergo one phase transition, to the cubic phase with the δ-Bi2O3 structure. The samples with the β-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 °C. The high-temperature (350-800 °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.