Relaxation phenomena in amorphous selenium-tellurium alloys

Amorphous specimens of selenium-tellurium alloys containing 0-35 at% Te were held for various times at temperatures ranging from room temperature to 318°K. Changes with time in the microhardness, density, small-angle X-ray scattering and heat capacity were determined. The hardness of crystalline specimens containing 0-100 at% Te and the density of crystalline specimens containing 0-30 at% Te were also measured. The microhardness and density of the amorphous specimens increased with time at room temperature to approximately constant values. With increasing time of annealing, the intensity of small-angle scattering decreased. Peaks developed in the heat capacity versus temperature curves; their height increased with time and decreased with temperature of annealing. The peaks moved to higher temperatures with increasing tellurium concentration. Changes in the enthalpy were determined from the heat capacities. The increases in microhardness, density and height of the heat capacity peaks reflect relaxation towards a more stable structure of smaller molecular mobility. The decrease in small-angle X-ray scattering indicates the disappearance of inhomogeneities in the density during the early stages of annealing. At a later stage, the enthalpy decreased with the most rapid change occurring over a narrow time interval. A spectrum of activation energies centered around 23 kcal (gram-atom)^-1 was derived. The effects of composition, temperature and time of annealing on the various properties are explained in terms of structural changes and relaxation kinetics.