Phase Stability, Phase Transformation Kinetics, and Conductivity of Y ₂ O ₃ —Bi ₂ O ₃ Solid Electrolytes Containing Aliovalent Dopants

Single‐phase, cubic solid solutions of baseline composition 25% Y ₂ O ₃ —75% Bi ₂ O ₃ with and without aliovalent dopants were fabricated by pressureless sintering of powder compacts. CaO, SrO, ZrO ₂ , or ThO ₂ was added as an aliovalent dopant. Sintered samples were annealed between 600° and 650°C for up to 4000 h. Samples doped with ZrO ₂ or ThO ₂ 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 ∼ 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 ZrO ₂ ‐ and ThO ₂ ‐doped samples is rationalized on the basis of suppressed interdiffusion on the cation sublattice.