Interdiffusion in the Quasi-Binary Systems Cd3te3/Ga2te3 and Hg3te3/Ga2te3

The quasibinary systems Cd3Te3/Ga2Te3 (I) and Hg3Te3/Ga2Te3 (II) form regions of extended solid solution. The interdiffusion of the cationic components in these regions is coupled with a flux of so-called structural vacancies. Peculiarities in the composition and temperature dependence of the interdiffusion coefficient, measured by an electron microprobe, are due to the effect of the thermodynamic factor. The calculation of the thermodynamic factor is based on a model of tetrahedral clusters. Special features of the phase diagrams of systems I and II are used to estimate the cluster energies. By use of these cluster energies the free excess enthalpy of the solid solution is calculated, and therefrom the thermodynamic factor can be derived. The course of the interdiffusion coefficient is caused by totally different influencies: in system I by a trend towards spinodal demixing, in system II by a trend towards ordering.