Determination of diffusion coefficient of Nd3+ in NdCrO3 based on solid state reaction

The solid state reaction, (1/2)Nd2O3 + (1/2)Cr2O3 --> NdCrO3, was studied b etween 1473 K and 1773 K in air to determine the parabolic rate constant. T he electrical conductivity of the NdCrO3 phases separately equilibrated wit h Nd2O3 and Cr2O3 were measured between 1673 K and 1773 K in an argon-oxyge n mixture. The standard Gibbs energy change for the solid state reaction wa s 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 stat e reaction, the standard Gibbs energy change of the solid state reaction, a nd the defect equilibrium reaction in NdCrO3. From these data, the diffusio n coefficient of Nd-3+ in NdCrO3 was given by DNd3+/m(2)s(-1) = 1.3 x 10(-6) (.) exp (-343 kJ mol(-1)/RT) (PO2/Pa)(3/16)a (1/8)Cr(2)O(3) where a(Cr2O3) is the activity of Cr2O3 and PO2 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.