Experimental determination of oxygen permeation flux through bulk and grain boundary of La_0.7Ca_0.3CrO₃

Oxygen permeation flux through La_0.7Ca_0.3CrO₃ was determined by an electrochemical method. Yttria-stabilized zirconia (YSZ) was used as an oxygen pump/sensor to apply an oxygen potential gradient over the sample, and the steady state current was recorded. The oxygen vacancy diffusion coefficient, D_v, was determined to be 1 × 10^-5 cm² s^-1 assuming a random defect model. The tracer exchange experiment was performed at 1273 K in ¹⁸O enriched O₂ (0.2 bar), and the sample was analyzed by a depth profiling and imaging technique using a secondary ion mass spectrometer (SIMS). The existence of fast diffusion paths along grain boundaries was confirmed. The bulk tracer diffusion coefficient, D^*, was calculated to be 2 × 10^-12 cm² s^-1 in air, which was about 6 times higher than that expected from the electrochemical measurement.