Effect of Ce-Doping on Thermoelectric Properties in PbTe Alloys Prepared by Spark Plasma Sintering

Abstract

Ce-doped Pb1−x Ce x Te alloys with x = 0, 0.005, 0.01, 0.015, 0.03, and 0.05 were prepared by induction melting, ball milling, and spark plasma sintering techniques. The structure and thermoelectric properties of the samples were investigated. X-ray diffraction (XRD) analysis indicated that the samples were of single phase with NaCl-type structure for x less than 0.03. The lattice parameter a increases with increasing Ce content. The lower Ce-doped samples (x = 0.005 and 0.01) showed p-type conduction, whereas the pure PbTe and the higher doped samples (x = 0, 0.015, 0.03, and 0.05) showed n-type conduction. The lower Ce-doped samples exhibited a much higher absolute Seebeck coefficient, but the higher electrical resistivity and higher thermal conductivity compared with pure PbTe resulted in a lower figure of merit ZT. In contrast, the higher Ce-doped samples exhibited a lower electrical resistivity, together with a lower absolute Seebeck coefficient and comparable thermal conductivity, leading to ZT comparable to that of PbTe. The lowest thermal conductivity (range from 0.99 W m−1 K−1 at 300 K to 0.696 W m−1 K−1 at 473 K) was found in the alloy Pb0.95Ce0.05Te due to the presence of the secondary phases, leading to a ZT higher than that of pure PbTe above 500 K. The maximum figure of merit ZT, in the alloy Pb0.95Ce0.05Te, was 0.88 at 673 K.