Transport properties of p-type CaMg2Bi2 thermoelectrics

摘要

Due to the complex crystal structure for low lattice thermal conductivity and the tunable valence bands for superior electronic performance, CaAl_(2)Si_(2)-structured AB_(2)C_(2) Zintl compounds have been frequently proven as promising p-type thermoelectric materials. In this work, thermoelectric properties of CaMg_(2)Bi_(2) are systematically investigated in a broad carrier concentration (10~(18)–10~(20)?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?×?10~(19)?cm~(?3), leading to a significant enhancement in electronic performance. With the help of additional point defect phonon scattering introduced by BaMg_(2)Bi_(2)-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 zT _(ave.) in addition to the contribution of a multiband transport. This work not only demonstrates CaMg_(2)Bi_(2) as a promising thermoelectric material, but also provides a well understanding of its underlying material physics.