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

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 (delta-phase); 0.33 <= x <= 0.55, 0.27 <= y <= 0.45, and 0.11 <= z <= 0.22 (delta'-phase). The delta- and delta'-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 (beta-phase) and with 0.45 <= x <= 0.6, 0.14 <= y <= 0.25, and 0.21 <= z <= 0.34 (beta'-phase). On heating to 900-1030 degrees C, the beta'-samples undergo a transition to a cubic phase with the delta-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 degrees 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 delta-Bi2O3 phase.