Properties of single crystalline AZn 2Sb 2 (A Ca,Eu,Yb)

Abstract

Single crystals of CaZn 2Sb 2, EuZn 2Sb 2, and YbZn 2Sb 2 were grown from melts of nominal composition AZn 5Sb 5 (A =Ca,Eu,Yb) with the excess melt being removed at 1073 K. The electrical transport properties are consistent with those previously reported for polycrystalline samples. This confirms that the p-type carrier concentrations ranging from 2 10 19 cm -3 to ∼1 × 10 20 cm -3 are intrinsic to these materials. Also consistent with transport in polycrystalline materials, the carrier mobility is found to be lowest in CaZn 2Sb 2, suggesting the trends in mobility and thermoelectric efficiency within these compounds are inherent to the material systems and not due to inhomogeneity or impurities in polycrystalline samples. These results suggest CaZn 2Sb 2 has the strongest coupling between the doping/defects and the electronic framework. Magnetization measurements reveal an antiferromagnetic transition near 13 K in EuZn 2Sb 2, and the observed magnetic anisotropy indicates the spins align parallel and anti-parallel to c in the trigonal lattice. Powder neutron diffraction on polycrystalline samples of CaZn 2Sb 2 and YbZn 2Sb 2 reveals smooth lattice expansion to 1000 K, with c expanding faster than a. The Debye temperatures calculated from specific heat capacity data and the isotropic displacement parameters are found to correlate with the carrier mobility, with the CaZn 2Sb 2 displaying the largest Debye temperature and smallest mobility. © 2012 American Institute of Physics.