Investigation of GeTe homegeneity region

High-temperature x-ray phtographic and metallographic studies of the homogenity region of GeTe have been carried out. The composition of the alloy was varied at intervals of 0.1% at.% in the range of 49.8 -51 at.% Te and at intervals of 0.2 at.% Te in the range 51 -52.6 at.% Te. The alloys were subjected to a homogenizing annealing. The x-ray and metallographic analysis showed that in alloys with up to 50.6 at.% Te there are two phases: rhomobohedral α-GeTe and Ge. Alloys with 50.7 and 50.8 at.%Te consist of one phase but in alloys with more than 50.8 at.% Te a second phase in addition to α-GeTe is found at the grain boundaries. In the x-ray phtographs new lines are found which give a hint for the appearance of γ-GeTe with a rhombic lattice. With an increase of the annealing temperature up to 3500C for the 51 at.% Te composition (with a subsequent quenching) the diffraction lines of γ-GeTe disappear in the x-ray photographs, and the lines of α-GeTe are blurred which is connected with the complex process of the phase transformations. The region of homogenity was also determined from the change of lattice parameters as a function of the composition for different temperatures. From this data the homogenity region of the low-temperature modification α-GeTe lies between 50.6-50.8 at.% Te, of the high-temperature phase β-GeTe at 6000C between 50.2 - 51.4 at.% Te. The temperature of the α→β phase transition is 400+-50C from the Ge side and 365+-50C from the Te side