Phase Diagram of the CdS-CdTe Pseudobinary System

There is a very narrow two-phase region in the CdS-CdTe pseudobinary system in high temperature, and we can obtain mixed crystals in almost the entire range of composition. Lattice parameters of CdS x Te 1- x satisfy "Vegard's law". Both of the solidus and the liquidus curves determined by D.T.A. have the same minimum temperature of 1071°C at x =0.2. At 1000°C the crystal structure is the cubic zincblende ( x <0.2) and the hexagonal wurtzite ( x >0.2). In the solid phase there is a miscibility gap, and it is attributed to lattice strain resulting from the large difference in atomic sizes of the VIth elements. On account of the strain energy contributions to the thermodynamic free energy the solidus curve is calculated from the experimental liquidus curve, and it agrees very well with the experimental data.