A thermodynamic investigation of crystalline and amorphous Se?Te alloys

The heats of formation, referred to the component elements in their stable crystalline forms, of crystalline Se?Te alloys containing 0 to 100 at. pct Te and amorphous alloys containing 0 to 30 at. pct Te were measured by liquid metal solution calorimetry. The heats of formation of the crystalline and amorphous alloys changed nonmonotonically with composition in a parallel manner. The crystalline alloys had negative heats of formation in the range of 0 to approximately 17 at. pct Te; the largest negative value of approximately?0.235 kcal/g-atom occurred at 10 at. pct Te. At 20 at. pct Te the heat of formation was positive and had a value of approximately 0.115 kcal/g-atom and at higher tellurium concentrations it again turned negative but was very small. The heats of formation of all amorphous alloys investigated were positive. A minimum of approximately 0.810 kcal/g-atom at 10 at.pct Te and a maximum of 1.040 kcal/g-atom at 20 at. pct Te corresponded to the largest negative value and the largest positive value of the heat of formation of the crystalline alloys of the respective compositions. The temperatures of maximum rates of crystallization and fusion and the heat effects associated with the crystallization and fusion of the amorphous alloys were measured by differential scanning calorimetry. With increasing tellurium concentration the temperature of crystallization decreased and the heat effect and the temperature associated with fusion increased.