STRUCTURAL PHASE-TRANSITIONS IN CU2-XTE CRYSTALS (X = 0.00, 0.10, 0.15, 0.20, 0.25)

Structural phase transitions in Cu2-xTe crystals have been investigated by high-temperature X-ray diffraction. At room temperature Cu2Te and Cu1.90Te specimens are two-phased, i.e. they consist of an orthorhombic phase with a = 7.319, b = 22.236, c = 36.458 angstrom and a hexagonal phase with a = 4.150, c = 7.188 angstrom. The changes in both compounds take place generally in the hexagonal phase with increasing temperature. At 821, 873 K they transform to a FCC phase. Monocrystals of the other compounds at room temperature crystallize in the hexagonal system and at 673, 773, 723 K, respectively, they transform to a FCC phase. It is determined that as the cation deficiency increases the crystal quality becomes better.