Realizing Excellent n- and p-Type Niobium-Based Half-Heusler Compounds Based on Thermoelectric Properties and High-Temperature Stability

Half-Heusler (HH) compounds are currently promising thermoelectric (TE) materials due to their outstanding performance. For reliable n- and p-type HH compounds, the dimensionless figure of merit zT is reported as greater than unity. However, to develop a high-performance TE module, zT, high-temperature stability, and compatibility of n- and p-type materials are key parameters. Here, the TE and thermomechanical properties and the high-temperature stability of Nb-based HH compounds: n-type Nb0.75M0.1CoSb and p-type FeNb0.9M0.1Sb (M = Ti, Zr, Hf) are investigated. The results reveal that the Ti-doped system exhibits better TE and thermomechanical properties than the Zr- and Hf-doped systems. Furthermore, the Ti-doped samples show good high-temperature stability in an inert atmosphere up to 773 K and in air up to 673 K. The performance of a 2 pi-module based on the best n-type Nb0.75Ti0.1CoSb and p-type FeNb0.9Ti0.1Sb is simulated by using the 3D finite element method. The maximum output power density (omega(max)) and conversion efficiency (eta(max)) of 2.3 W cm(-2) and 4.0%, respectively, are obtained when the cold- and hot-side temperatures are 298 and 773 K, respectively.