Entropy engineering: A simple route to both p- and n-type thermoelectrics from the same parent material

Abstract

Ternary half-Heusler (HH) semiconductors have been identified as excellent high-temperature thermoelectric (TE) materials, but the high thermal conductivity restricts the development and application. In this work, we report the design of the HH alloy Ti(Fe/Co/Ni)Sb with both p-type and n-type conductions from the same parent compound TiCoSb by entropy engineering. High-throughput (HTP) experiments have been first conducted to verify the formation of Ti(Fe1/3+xCo1/3Ni1/3-x)Sb solid solution and screen the range of compositions with the best p-type and n-type thermoelectric properties by regulating the Fe/Ni ratio. The random mixing of Fe/Co/Ni on the 4c site of the HH lattice induces a large lattice distortion, leading to a significantly reduced lattice thermal conductivity. Adjusting the sample composition (Fe/Ni ratio) changes the carrier concentration, carrier type and electronic band structure simultaneously, contributing to improved TE power factors for both p- and n-type materials. As a result, a peak TE figure of merit zT of up to ∼0.56 for p-type and ∼0.49 for n-type are achieved. Our experimental results demonstrate that entropy engineering is a promising strategy to extend the composition range and tune the TE properties for HH materials, which might be a generally applicable route to improve the thermoelectric performance of other TE materials.