Gradient composite thermoelectric materials

Gradient composition is one of the strategies for increasing the figure of merit Z of thermoelectric (TE) materials. There are two types of gradient composition TE materials. One is a carrier concentration functionally graded material (FGM), in which the carrier concentration was optimized to produce the maximum local Z with a certain temperature gradient. The other is a segmented FGM, which was composed of different material and each segment works at its optimal temperature range. The study progress of those two types of TE FGM is reviewed.