Layer growth of ZnSb phase in the Zn-Sb diffusion couple at high pressure

Abstract

The kinetics of growth of the ZnSb phase layer in the Zn-Sb system has been investigated with the diffusion couples annealed in the temperature range of 240 to 320℃, under pressures up to 30 kb and for time up to 17 hr. Among all the intermetallic compounds present in the Zn-Sb equilibrium phase diagram, only ZnSb was the product detected in the diffusion zone. Concentrations of zinc in the ZnSb layer were 20-35 at%, which deviated extensively from the equilibrium concentration. Zinc was by far the faster moving species and the pronounced Kirkendall effect was observed. Since the parabolic rate law was obeyed and the Kirkendall markers moved toward the zinc side, it was concluded that volume diffusion controlled the layer growth and occurred by vacancy mechanism. It has been found that pressure affects not only the growth of the ZnSb phase, but also the interface composition; the increase of 8 kb in the applied pressure reduces the rate constant by about 7% and the increase of pressure from 14 to 22 kb decreases by about 7% the concentration of zinc in the ZnSb layer. The apparent activation energies and the activation volumes are 12.1-14.3 kcal/mol in the range of 240-320℃ and 0.9-1.2cm^3/mol in the range of 14-30 kb, respectively. The diffusion coefficients of zinc calculated by using Kidson's method were 10^-9 - 10^-10 cm^2/sec and they were 5-10 times as large as those obtained in the Zn-As system.