Order-disorder transition in CdGa2Se4-CdIn2Se4s solid solutions

A transition of the order-disorder type in the CdGa2Se4-CdIn2Se4 alloy is studied. The X-phase, microstructural and differenital-thermal analyses made it possible to obtain the polythermal cross section of CdGa2Se4-CdIn2Se4. Over the whole concentration range the existence of solid solutions and the phase transformation from the low-temprature modification α into the high-temperature one α' are found. Data on concentration dependence of the phase transformation temperature, the parameter of tetragonal compression and expansion coefficients in different directions are presented. The structural variation of α-α' leads to the variation of the shape and the volume of the elementary cell and decrease of its symmetry from cubic to tetragonal one. The data also give an evidence that the α-α' transformation is of the first kind