Anisotropy and thermal stability of hot-forged BICUTIVOX oxygen ion conducting ceramics

The oxygen ion conductivity of ultra dense, hot forged Bi4(MexV1−x)2O11 (BIMEVOX) ceramics is reported for the first time. A novel approach to electrode preparation, including laser trenching, was developed to perform 4-probe impedance spectroscopy and determine conductivity of small bar-shaped samples with high accuracy and precision. Hot forged (HF) Bi4(Cu0.05Ti0.05V0.90)2O11 (BICUTIVOX) ceramic, with modest preferred orientation (11%), exhibits anisotropy by a factor of 2 in its conductivity. Brick layer model (BLM) analysis of complex impedance plots reveals that the relative contribution of grains and grain boundaries to the total resistance is direction dependent, in the low temperature γ′ phase. The total ionic conductivity of BICUTIVOX, prepared either by hot-forging or conventional sintering, appears to be stable with thermal aging and cycling. Anisotropy in the thermal expansion of polycrystalline BIMEVOX ceramics is also reported.