Determination of Diffusion Coefficient of Nd³⁺ in NdCrO₃ Based on Solid State Reaction

Abstract

The solid state reaction, (1⁄2)Nd₂O₃+(1⁄2)Cr₂O₃→NdCrO₃, was studied between 1473 K and 1773 K in air to determine the parabolic rate constant. The electrical conductivity of the NdCrO₃ phases separately equilibrated with Nd₂O₃ and Cr₂O₃ were measured between 1673 K and 1773 K in an argon-oxygen mixture. The standard Gibbs energy change for the solid state reaction was estimated from the activity dependence of the electrical conductivity of NdCrO₃. According to Wagner’s theory, the diffusion coefficient of Nd³⁺ in NdCrO₃ can be evaluated from the parabolic rate constant for the solid state reaction, the standard Gibbs energy change of the solid state reaction, and the defect equilibrium reaction in NdCrO₃. From these data, the diffusion coefficient of Nd³⁺ in NdCrO₃ was given by D_Nd^3+/m^2s^-1 = 1.3 ×10^-6 ·exp\\left(-\\frac343 kJ mol^-1RT \\ ight) (P_O_2/Pa)^3/16 a_Cr_2O_3^1/8where a_Cr2O3 is the activity of Cr₂O₃ and P_O2 is the oxygen pressure. The obtained diffusion coefficient of Nd³⁺ in NdCrO₃ was compared with that of Y³⁺ in YCrO₃ and that of La³⁺ in LaCrO₃.