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arXiv 1202.4004cond-mat.mtrl-scicond-mat.other
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单晶AZn2Sb2(A=Ca,Eu,Yb)的性质

Properties of single crystalline AZn2Sb2 (A=Ca,Eu,Yb)

Andrew F. May, Michael A. McGuire, Jie Ma, Olivier Delaire, Ashfia Huq, Radu Custelcean

摘要:

在1073 K下,从AZn_5Sb_5(A=Ca,Eu,Yb)熔体中生长出CaZn_2Sb_2,EuZn_2Sb_2和Yb_2 Zn_2Sb_2单晶。电输运性质与先前报道的多晶样品一致。这证实了$p$型载流子浓度范围为2 × 10 ^{19}cm^{-3}至~ 1 × 10 ^{20}cm^{-3}是这些材料固有的。还一致的多晶材料中的运输,载流子迁移率被发现是最低的CaZn 2Sb 2,这表明在这些化合物内的迁移率和热电效率的趋势是固有的材料系统,而不是由于多晶样品中的不均匀性或杂质。这些结果表明,CaZn_2Sb_2具有最强的掺杂/缺陷和电子骨架之间的耦合。磁化强度测量表明EuZn_2Sb_2在13 K附近发生了反铁磁转变,磁各向异性表明在三角晶格中自旋与$c$平行和反平行排列.对CaZn 2 Sb 2和Yb Zn 2 Sb 2多晶样品的粉末中子衍射表明,晶格膨胀到1000 K时是平滑的,其中$c$膨胀比$a$快。从比热容数据和各向同性位移参数计算的德拜温度被发现与载流子迁移率,与CaZn 2Sb 2显示最大的德拜温度和最小的流动性。

英文摘要:

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.

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