Thermal conductivity, electrical conductivity, and thermoelectric properties of CdTe and Cd0.8Zn0.2Te crystals between room temperature and 780oC

The thermal conductivity, electrical conductivity, and Seebeck coefficient of a vapor-grown CdTe and two melt-grown Cd0.8Zn0.2Te crystals, including In-doped CZT-30 and un-doped CZT-34 samples, were measured from room temperature to 780oC. The measured thermal conductivity of CdTe was higher than the two CdZnTe samples in the low temperature range and the three sets of data merged together at temperature above 750oC. The measured electrical conductivities of CdTe and CZT-30 were close to be intrinsic from 190oC to 780oC. The CZT-34 sample showed higher electrical conductivity value at 290oC and merged with the data of CZT-30 at temperatures above 650oC. The measured Seebeck coefficients for all three samples showed high positive values, between 0.9 and 1.1mV/K, in the intermediate temperature range between 350 and 550oC and, as temperature increased, decreased slowly and converted to n-type. The Figure of Merit for the thermoelectric application, zT, calculated for the three samples were orders of magnitude lower than the state-of-the-art p-type thermoelectric materials mainly due to the low values of the electrical conductivity. A rough estimate was made on the hole concentration needed to improve the value of zT for CdTe to 1.0 at 500oC. A simple interpolation and extrapolation of the present data gives the value of zT for the n-type intrinsic CdTe to be 1.2±0.4 at 1050oC.