MX_(n)半导体层状材料层间热电性质预测

Prediction of Interlayer Thermoelectric Properties of MX_(n) Semiconductor Layered Materials

优质的热电材料要求具有“声子玻璃、电子晶体”特性,因此,基于第一性原理计算,提出在二元MX_(n)半导体层状材料中筛选具有上述特性材料的方法。因层间为范德华作用力,层状材料中面外方向的晶格热导率都非常低,是良好的“声子玻璃”材料。而面外方向的电子输运能力与M元素和原子距离相关。M为主族元素时(例如SnSe),因非局域的p_(z)轨道和较小的原子层间距离(小于4Å)使电子具有良好的层间输运性能。当M为过渡金属元素时(例如MoS_(2)),局域的d轨道和较大的阳离子层间距(大于6Å)使得电子无法在层间传输。通过阳离子M的层间距离大小和类型(主族元素还是过渡金属)可以对层状材料面外方向的热电性质进行判断,为筛选出有潜力的高ZT热电材料提供理论指导。

Based on the fact that high quality thermoelectric materials require the combined characteristics of“phonon glass with electronic crystal”,and according to the first principle calculation,a new method has thus been proposed for screening materials with the above characteristics in binary MX_(n) semiconductor layered materials.Due to the weak van der Waals force between the layers,the lattice thermal conductivity in the out-of-plane direction is very low,making it a good“phonon glass”material,with the electron transport ability in the out-of-plane direction related to the M element and the atomic distance.With M being the main group element(e.g.SnSe),electrons are characterized with a good interlayer transport property due to the non-local p_(z) orbital and the small interlayer distance(<4Å).With M being a transition metal element(e.g.MoS_(2)),the local d orbitals and the large cation-layer spacing(>6Å)make it impossible for electrons to travel between layers.The thermoelectric properties of the layered material in the outof-plane direction can be judged by the size and type of the interlayer distance of the cation M(main group element or transition metal),thus providing a theoretical guidance for screening potential high-ZT thermoelectric materials.