Grain-boundary diffusion of strontium in (La,Ca)CrO₃ perovskite-type oxide by SIMS

The grain-boundary-diffusion coefficient (D_gb) of strontium in La_0.9Ca_0.13CrO_3-δ was determined by secondary-ion mass spectrometry (SIMS), using two different measurement modes: depth profiling from the surface and line scanning on the fracture surface. The depth profiles that were sputtered by an O₂⁺-primary-ion beam gave two slopes of strontium concentration profiles, which corresponded to grain (bulk) and grain-boundary diffusion. The depth profiles were fitted to an appropriate equation that gave the grain- (bulk-) and grain-boundary-diffusion coefficients (D_bulk = 6.5 × 10^-20 m²/s and D_gb = 1.6 × 10^-15 m²/s in air at 1273 K, respectively). Initially, to obtain the D_gb value via the SIMS line-scanning measurement, the fracture surface of La_0.9Ca_0.13CrO_3-δ was measured by a low-energy O₂⁺-primary-ion beam. The line-scanning measurement enabled us to successfully determine the strontium concentration profiles around the grain boundary. However, the D_gb value that was obtained via the line-scanning mode was 6.0 × 10^-13 m²/s, which was a factor of 100 greater than that which was obtained by the depth-profile mode. Comparison between the depth-profile and line-scanning modes will require additional careful examination.