Anomaly in the specific heat of lead tellurides

Specific heats of two types of lead tellurides, namely p-type Pb1-xSnxTe (x = 0.0, 0.1, 0.3, 0.5, 0.7, 0.9, 1.0) and n-type PbTe doped with y mass% PbI2 (y = 0.0, 0.2, 0.5, 0.8, 1.0) were observed in the temperature range from 50 to 500 degreesC by using a differential scanning calorimeter (DSC). The specific heat of pure Te is also observed in the same temperature range to confirm the dominance of Te. At lower temperatures below 200 degreesC, all the observed data were fairly consistent with those predicted on the basis of the Dulong-Petit's law, while above 200 degreesC, the observed data showed curious temperature dependences. At high temperatures above 200 degreesC, DSC analysis, with the aid of the experiment on pure Te, revealed an anomalously large specific heat that can be predicted from the Schottky defects caused by decomposition and sublimation of Te. In the n-type case, the anomaly in the specific heats is rather smaller than that in the p-type case, which fact suggested the dopant PbI2 may suppress the decomposition and sublimation of Te from lead tellurides.