Improved carrier concentration control in Zn-doped Ca5Al2Sb6

Ca5Al2Sb6 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 Ca5-xNaxAl2Sb6, this work investigates doping with Zn2+ on the Al3+ site (Ca5Al2-xZnxSb6). 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. Ca5Al2-xZnxSb6 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. (C) 2011 American Institute of Physics. [doi:10.1063/1.3607976]