High thermoelectric performance of GeTe–Ag8GeTe6 eutectic composites

The (GeTe)1−x(Ag8GeTe6)x composites with x = 0.02, 0.05, 0.08 and 0.11 were prepared by melting, ball milling and spark plasma sintering techniques. The thermoelectric properties of the composites were investigated. The experimental results show that all samples are composites consisting of the primary solidification phase GeTe and eutectic microstructures with GeTe and Ag8GeTe6 phases. The composites are p-type semiconductors. As compared to the pure compound GeTe, the existence of Ag8GeTe6 compound in the GeTe phase enhances its electrical resistivity at low temperatures while reduces its electrical resistivity at high temperatures. Also, the Seebeck coefficient of the composite is slightly decreased due to the Ag8GeTe6 compound, but its thermal conductivities are reduced significantly. As a result, the figure of merit ZT for the materials can be enhanced. The maximum figure of merit ZT was obtained as 1.15 in the sample (GeTe)0.89(Ag8GeTe6)0.11 at 673 K. This value is much higher than that for the pure GeTe, leading to a substantial improvement in the thermoelectric performance of the material.

► Pb-free (GeTe)1−x(Ag8GeTe6)x composites have been prepared by melting, ball milling and spark plasma sintering.
► The existence of Ag8GeTe6 compound in the GeTe phase reduces its thermal conductivities significantly.
► The maximum figure of merit ZT was obtained as 1.15 in the sample (GeTe)0.89(Ag8GeTe6)0.11 at 673 K.