INTERDIFFUSION STUDIES IN SYSTEM MGO-CR2O3

The rate of formation of single crystal MgCr2O4 from MgO single crystal and polycrystalline Cr2O3 in air can be described by the expression k = 16.3 exp(80,000±9,000/RT) cm2 sec-1. The single crystal of MgCr2O4 grew by the advancement of(110) planes at the MgCr2O4/Cr2O3 interface. Two different methods were used for the calculation of interdiffusion coefficients of Cr3+ in MgO in the temperature range 1340-1640°C. Wagner's recent analysis was applied for the calculation of interdiffusion coefficients in the MgO-Cr2O3 system where an intermediate spinel phase exists. A different mathematical treatment was derived for the calculation of interdiffusion coefficients at the saturation concentration of Cr2O3, in MgO single crystal. The interdiffusion coefficients increased linearly with increasing mole fraction of Cr3+ cations and with increasing mole fraction of cation vacancies. For a concentration of one mol.% Cr2O3 MgO, the interdiffusion coefficient can be expressed as D = 5·50 × 10-3 exp(67,000 ±2,000/RT) cm2 sec-1. The enthalpy of activation was independent of cation vacancy concentration while the entropy of activation increased with increasing vacancy concentration. The measured interdiffusion coefficients were deduced to be the intrinsic diffusion coefficients for Cr3+ cations in MgO. Interdiffusion coefficients were in the range of 10-12-10-9cm2sec-1 for the temperatures and concentrations studied. © 1969.