Stabilized Bi2O3-based phases in the Bi2O3–Pr2O3–MoO3 system and their electrical properties

Abstract The formation of Bi2O3-based compounds with the general formula (Bi2O3)x(Pr2O3)y(MoO3)z (x + y + z = 1) in the ternary system Bi2O3–Pr2O3–MoO3 has been studied using samples prepared by solid-state reactions in air, followed by slow cooling. The results demonstrate that, in this system, phases with a monoclinic, tetragonal, or cubic fluorite structure can be stabilized, when bismuth oxide is co-doped with molybdenum and praseodymium. Two stability fields of cubic phases have been identified: 0.6 ≤ x ≤ 0.93, 0.02 ≤ y ≤ 0.2, and 0.02 ≤ z ≤ 0.26 (δ-phase); 0.33 ≤ x ≤ 0.55, 0.27 ≤ y ≤ 0.45, and 0.11 ≤ z ≤ 0.22 (δ'-phase). The δ- and δ'-phases have identical X-ray powder diffraction patterns but differ in properties. Two tetragonal phases exist in the system, with 0.94 ≤ x ≤ 0.97 (β-phase) and with 0.45 ≤ x ≤ 0.6, 0.14 ≤ y ≤ 0.25, and 0.21 ≤ z ≤ 0.34 (β'-phase). On heating to 900–1030 °C, the β'-samples undergo a transition to a cubic phase with the δ-Bi2O3 structure, which is accompanied by a lambda-type anomaly in permittivity, characteristic of ferro- or antiferroelectrics. The electrical conductivity of the samples increases with Bi2O3 concentration. The highest conductivity in the Bi2O3–Pr2O3–MoO3 system (0.4 S/cm at 800 °C) is offered by the cubic material (Bi2O3)0.8(Pr2O3)0.1(MoO3)0.1. A monoclinic phase isostructural with Bi3.24La2W0.76O10.14 have been found in a narrow region near the cubic δ-Bi2O3 phase.