Andrew F. May, Michael A. McGuire, Jie Ma, Olivier Delaire, Ashfia Huq, Radu Custelcean
Single crystals of CaZn2Sb2, EuZn2Sb2, and YbZn2Sb2 were grown from melts of
nominal composition AZn5Sb5 (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 2x10^{19}cm^{-3} to
~1x10^{20}cm^{-3} are intrinsic to these materials. Also consistent with
transport in polycrystalline materials, the carrier mobility is found to be
lowest in CaZn2Sb2, 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 CaZn2Sb2 has the strongest coupling between the doping/defects and the
electronic framework. Magnetization measurements reveal an antiferromagnetic
transition near 13\,K in EuZn2Sb2, 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 CaZn2Sb2 and
YbZn2Sb2 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 CaZn2Sb2 displaying the largest Debye temperature
and smallest mobility.
View original:
http://arxiv.org/abs/1202.4004
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