Pressure-induced improvement of grain boundary properties in yttrium-doped BaZrO₃

Yttrium-doped BaZrO₃ (BZY) is a promising electrolyte for intermediate-temperature protonic ceramic fuel cells. However, BZY exhibits a high resistance because of the blocking effect of the grain boundaries. In this study, the effect of pressure on undoped and 5% yttrium-doped BaZrO₃ (BZY0 and BZY5) were investigated at 0.45–24.01 GPa and 273–673 K with a diamond anvil cell. Their bulk, grain boundary, and total electrical conductivities were determined by impedance spectroscopy and direct-current resistance measurement. Both samples tended to show increasing electrical conductivity with increasing pressure, although each showed a discontinuous inflexion point (at ∼14.54 GPa for BZY0 and at ∼11.11 GPa for BZY5) indicating a phase transition from a cubic to a tetragonal structure. The samples showed a 3.43 GPa difference in the onset pressure of the structure change. Characteristic parameters, including space charge potential, relaxation frequency, and transport activation energy, were obtained before and after the phase transition. The results suggest that pressure significantly improves oxygen ion conduction in acceptor-doped perovskites oxides. (paper)