Transport properties of p-type CaMg2Bi2 thermoelectrics

Abstract

Due to the complex crystal structure for low lattice thermal conductivity and the tunable valence bands for superior electronic performance, CaAl2Si2-structured AB2C2 Zintl compounds have been frequently proven as promising p-type thermoelectric materials. In this work, thermoelectric properties of CaMg2Bi2 are systematically investigated in a broad carrier concentration (1018–1020 cm−3) through Ag-doping for comprehensively evaluating its potential for thermoelectric applications. The broad carrier concentration enables a well assessment of the carrier transport properties by single parabolic band with acoustic phonon scattering and a revelation of the carrier transport by multiple valence orbitals when the carrier concentration higher than ∼2 × 1019 cm−3, leading to a significant enhancement in electronic performance. With the help of additional point defect phonon scattering introduced by BaMg2Bi2-alloying, a reduction in lattice thermal conductivity in the entire temperature range and the lowest one of ∼0.7 W/m-K are achieved, leading to a 100% enhancement in average zTave. in addition to the contribution of a multiband transport. This work not only demonstrates CaMg2Bi2 as a promising thermoelectric material, but also provides a well understanding of its underlying material physics.