Key Laboratory of Transparent Opto-Functional Inorganic Materials of Chinese Academy of Sciences, Shanghai Institute of Ceramics, 1295 Ding Xi Road, Shanghai, 200050, PR China.
Dalton Trans. 2011 Oct 21;40(39):10007-13. doi: 10.1039/c1dt10721f. Epub 2011 Sep 6.
An efficient route to construct a three-dimensional crystal structure is stacking of two-dimensional building blocks (2D-BBs). The crystal structures of potential thermoelectric compounds REOZnSb (RE = La, Ce, Pr, Nd) were virtually constructed from insulating [REO] and conducting [ZnSb] layers. Further optimizations performed by means of first-principles calculations show that REOZnSb should exhibit semimetal or narrow band-gap semiconductor behaviors, which is a prerequisite for high thermoelectric efficiency. The analysis of the electron localizability indicator for LaOZnSb reveals mostly covalent polar interactions between all four kinds of atoms. The electron density yields completely balanced ionic-like electronic formula La(1.7+)O(1.2-)Zn(0.4+)Sb(0.9-). Furthermore, the samples of REOZnSb have been synthesized via solid-state reaction, and their crystal structures were confirmed by powder X-ray diffraction. The differences in cell parameters between the theoretically optimized and the experimental values are smaller than 2%. The temperature dependence of the magnetic susceptibility shows that LaOZnSb is diamagnetic above 40 K, whereas CeOZnSb, PrOZnSb and NdOZnSb are Curie-Weiss-type paramagnets. Electrical conductivity and Seebeck effect measurements indicate that REOZnSb are p-type semiconductors. A considerably high Seebeck coefficient and low thermal conductivity were obtained for pure LaOZnSb, but its low electrical conductivity leads to a small ZT. The high adjustability of the crystal structure as well as properties by optimization of the chemical composition in the compounds REOZnSb provide good prospects for achieving high thermoelectric efficiency.
构建三维晶体结构的有效途径是二维构建块（2D-BBs）的堆叠。潜在热电化合物 REOZnSb（RE = La、Ce、Pr、Nd）的晶体结构是由绝缘[REO]和导电[ZnSb]层虚拟构建而成。通过第一性原理计算进一步优化表明，REOZnSb 应该表现出半金属或窄带隙半导体行为，这是实现高热电效率的前提。对 LaOZnSb 的电子局域化指标的分析表明，所有四种原子之间主要存在共价极性相互作用。电子密度给出了完全平衡的类离子电子公式 La(1.7+)O(1.2-)Zn(0.4+)Sb(0.9-)。此外，通过固态反应合成了 REOZnSb 样品，并通过粉末 X 射线衍射证实了它们的晶体结构。理论优化和实验值之间的晶胞参数差异小于 2%。磁化率的温度依赖性表明，LaOZnSb 在 40 K 以上为抗磁性，而 CeOZnSb、PrOZnSb 和 NdOZnSb 为居里-外斯型顺磁性。电导率和 Seebeck 效应测量表明，REOZnSb 是 p 型半导体。纯 LaOZnSb 具有相当高的 Seebeck 系数和低导热系数，但低电导率导致 ZT 较小。化合物 REOZnSb 中通过化学成分优化来调整晶体结构和性能的高度可调性为实现高热电效率提供了良好的前景。
