Thermoelectric Properties of Fine-Grained Germanium Telluride

We studied the microstructure and the thermoelectric properties of the materials based on p-type germanium telluride doped with copper and bismuth and obtained by hot pressing of three type powders prepared by ingot grinding in a planetary mill, their sizes being from hundreds of microns (0.315-mm cell) to hundreds of nanometers (mechanical activation) and by melt spinning. We studied the microstructure, the chips and the composition of the samples by optical and scanning electron microscopy. By the diffractometric and the micro X-ray phase analyses, we revealed the presence of copper oxide and germanium precipitation in the samples. The samples obtained from the powder prepared by the mechanical activation had the largest number of grains with the sizes less than units of microns. We measured the following thermoelectric parameters of the materials: the Seebeck coefficient and the specific electrical and thermal conductivity within the temperature range of 300-800 K. We calculated the coefficient of thermoelectric efficiency ZT; the hot-pressed samples obtained from the powders produced by the melt spinning had the highest value: ZT = 1.5 at 600 K.