Quarez Eric, Hsu Kuei-Fang, Pcionek Robert, Frangis N, Polychroniadis E K, Kanatzidis Mercouri G
Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, USA.
J Am Chem Soc. 2005 Jun 29;127(25):9177-90. doi: 10.1021/ja051653o.
The nature of the thermoelectric materials Ag(1-x)Pb(m)SbTe(m+2) or LAST-m materials (LAST for Lead Antimony Silver Tellurium) with different m values at the atomic as well as nanoscale was studied with powder/single-crystal X-ray diffraction, electron diffraction, and high-resolution transmission electron microscopy. Powder diffraction patterns of different members (m = 0, 6, 12, 18, infinity) are consistent with pure phases crystallizing in the NaCl-structure-type (Fmm) and the proposition that the LAST family behaved as solid solutions between the PbTe and AgSbTe2 compounds. However, electron diffraction and high resolution transmission electron microscopy studies suggest the LAST phases are inhomogeneous at the nanoscale with at least two coexisting sets of well-defined phases. The minority phase which is richer in Ag and Sb is on the nanosized length scale, and it is endotaxially embedded in the majority phase which is poorer in Ag and Sb. Moreover, within each nanodomain we observe extensive long range ordering of Ag, Pb, and Sb atoms. The long range ordering can be confirmed by single crystal X-ray diffraction studies. Indeed, data collections of five different single crystals were successfully refined in space groups of lower symmetry than Fmm including P4/mmm and Rm. The results reported here provide experimental evidence for a conceptual basis that could be employed when designing high performance thermoelectric materials and dispel the decades long belief that the systems (AgSbTe2)(1-x)(PbTe)x are solid solutions.
利用粉末/单晶X射线衍射、电子衍射和高分辨率透射电子显微镜，研究了具有不同m值的热电材料Ag(1-x)Pb(m)SbTe(m+2)或LAST-m材料（LAST代表铅锑银碲）在原子尺度和纳米尺度上的性质。不同成员（m = 0、6、12、18、无穷大）的粉末衍射图谱与在NaCl结构类型（Fmm）中结晶的纯相以及LAST族表现为PbTe和AgSbTe2化合物之间的固溶体这一观点一致。然而，电子衍射和高分辨率透射电子显微镜研究表明，LAST相在纳米尺度上是不均匀的，至少有两组明确共存的相。富含Ag和Sb的少数相处于纳米尺寸长度尺度，并且它以同轴方式嵌入到富含Ag和Sb的多数相中。此外，在每个纳米域内，我们观察到Ag、Pb和Sb原子存在广泛的长程有序排列。这种长程有序排列可以通过单晶X射线衍射研究得到证实。实际上，五个不同单晶的数据收集成功地在比Fmm对称性更低的空间群（包括P4/mmm和Rm）中进行了精修。这里报道的结果为设计高性能热电材料时可以采用的概念基础提供了实验证据，并消除了数十年来关于(AgSbTe2)(1-x)(PbTe)x体系是固溶体的信念。
