Investigation of structural transformations in Cu 2 Se

Structural transformations in Cu 2 Se have been studied by the method of hightemperature roentgenography. From a diffraction record of reflection angles and from a Debye‐powder pattern the unit‐cell parameters of a rhombic α‐modification have been calculated at temperatures of 25, 50, 100, and 132 °C. Using the diffraction line (027) disappearing under the α → β transformation and appearing again in the course of the inverse β → α transformation it has been found that the equilibrium temperature between the α‐ and β‐modifications is T 0 = 134 ± 0.5 °C. The unit cell parameter of a hightemperature face‐centered cubic β‐modification at temperatures of 150, 200, 250, and 300 °C also has been determined. In the course of mutual transformations a rigid orientational linkage has been found to exist between the α‐ and β‐modifications. It has been discovered that when the multiplicity of α → β and β → α transformations n reaches a value of approximately 30, a β‐Cu 2 Se → Cu 2 – x Se transformation (where x = 0.20) takes place which is not followed by an inverse transformation.