Solid-state reaction kinetics of LaCrO3 from the oxides and determination of La3+ diffusion coefficient

The parabolic rate constant for the solid-state reaction of 1/2La(2)O(3) + 1/2CrO(3) = LaCrO3 was measured at temperatures between 1483 and 1688 K in air and at 1695 K in oxygen pressures between 2.1 x 10(4) and 1.5 x 10(-5) Pa. According to Wagner's theory, the diffusion coefficient of La3+ in LaCrO3 was evaluated using the parabolic rate constant and the standard Gibbs energy change of the reaction. The oxygen pressure dependence of the diffusion coefficient is given by DLa3+/m(2) s(-1) = 4.5 x 10(-16) (P-O2/Pa)(3/16) a(Cr2O3)(1/8) + 1.6 x 10(-16) a(Cr2O3)(1/5) (T = 1695 K) where a(Cr2O3) is the activity of Cr2O3 and P-O2 is the oxygen pressure. The temperature dependence of the diffusion coefficient of lanthanum ion in LaCrO3 is given by DLa3+/m(2) s(-1) = 2.3 x 10(-1) exp (- 480 kJ mol(-1)/RT)(P-O2/Pa)(3/16) a(Cr2O3)(1/8) (at higher P-O2, e.g., P-O2 > 10(3) Pa at 1695 K).