PHASE-STABILITY, PHASE-TRANSFORMATION KINETICS, AND CONDUCTIVITY OF Y2O3-BI2O3 SOLID ELECTROLYTES CONTAINING ALIOVALENT DOPANTS

Single-phase, cubic solid solutions of baseline composition 25% Y2O3-75% Bi2O3 with and without aliovalent dopants were fabricated by pressureless sintering of powder compacts. CaO, SrO, ZrO2, or ThO2 was added as an aliovalent dopant. Sintered samples were annealed between 600-degrees and 650-degrees-C for up to 4000 h. Samples doped with ZrO2 or ThO2 remained cubic, depending upon the dopant concentration, even after long-term annealing. By contrast, undoped, CaO-doped, and SrO-doped samples transformed to the low-temperature, rhombohedral phase within approximately 200 h. Conductivity measurements showed no degradation of conductivity in samples that did not undergo the transformation. In samples that underwent the transformation, a substantial decrease in conductivity occurred. The enhanced stability of the ZrO2- and ThO2-doped samples is rationalized on the basis of suppressed interdiffusion on the cation sublattice.