Improved carrier concentration control in Zn-doped Ca_5Al_2Sb_6

Abstract

Ca_5Al_2Sb_6 is an inexpensive, Earth-abundant compound that exhibits promising thermoelectric efficiency at temperatures suitable for waste heat recovery. Inspired by our previous study of p-type Ca_(5−x)Na_xAl_2Sb_6, this work investigates doping with Zn^(2+) on the Al^(3+) site (Ca_5Al_(2−x)Zn_xSb_6). We find Zn to be an effective p-type dopant, in contrast to the low solubility limit and poor doping efficiency of Na. Seebeck coefficient measurements indicate that the hole band mass is unaffected by the dopant type in the high-zT temperature range. Band structure and density of states calculations are employed in order to understand the carrier concentration-dependent effective mass. Ca_5Al_(2−x)Zn_xSb_6 has a low lattice thermal conductivity that approaches the predicted minimum value at high temperature (1000 K) due to the complex crystal structure and high mass contrast.

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