Determination of Diffusion Coefficient of Nd<SUP>3+</SUP> in NdCrO<SUB>3</SUB> Based on Solid State Reaction

Abstract

The solid state reaction, (1 /2 )Nd 2 O 3 + (1/2)Cr 2 O 3 → NdCrO 3 , was studied between 1473 K and 1773 K in air to determine the parabolic rate constant. The electrical conductivity of the NdCrO 3 phases separately equilibrated with Nd 2 O 3 and Cr 2 O 3 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 NdCrO 3 According to Wagner's theory, the diffusion coefficient of Nd 3+ in NdCrO 3 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 NdCrO 3 . From these data, the diffusion coefficient of Nd 3 in NdCrO 3 was given by D Ma3+ /m 2 s -1 = 1.3 × 10 -6 .exp(-343 kJ mol -1 /RT) (P O2 /Pa) 3/16 a 1/8 Cr2O3 where a Cr2O3 is the activity of Cr 2 O 3 and P O2 is the oxygen pressure. The obtained diffusion coefficient of Nd 3+ in NdCrO 3 was compared with that of Y 3+ in YCrO 3 and that of La 3+ in LaCrO 3 .