【作者】 张俊；

【导师】 谢逸群；

【作者基本信息】 上海师范大学 ， 凝聚态物理， 2021， 硕士

【摘要】 近年来,二维热电材料因其无噪声,温度可控,使用寿命长等优点吸引了广泛的研究兴趣。开发室温热电优值（ZT）大于1.0的二维热电材料是目前热电研究领域的一个重要方向。本文主要采用第一性原理方法研究二维单层PtX₂（X=O,S,Se,Te）及YSi₂N₄（Y=Ti,Zr,Hf）的热电性质,获得ZT随温度的变化规律,得到室温高ZT,并阐明机理。主要研究内容和结果如下:首先计算了四种单层PtX₂的电子能带、声子谱及热电性质。结果表明,这些材料具有稳定结构,属于间接带隙半导体,其HSE06带隙在0.5～3.5 e V之间。与其它多种二维半导体相比,PtX₂具有较低的晶格热导率,在0.207 WK^-1M^-1到0.643 WK^-1M^-1之间。这使得它们在300 K时有较大的ZT,分别为:1.65（Pt Te₂）、1.42（Pt S₂）、0.94（Pt O₂）和0.84（Pt Se₂）。此外,对晶格施加1%的拉伸应变后,仍可获得1.29（Pt S₂）和1.02（Pt Te₂）的高ZT（300 K）。这些结果表明,二维单层PtX₂是一种有潜力的室温热电材料。本文还研究了二维单层YSi₂N₄（Y=Ti,Zr,Hf）的热电性质。这些材料都拥有间接带隙,在0.1～2.0 e V之间。相比于四种单层PtX₂材料,单层YSi₂N₄的热导率大了约一个数量级,因此ZT较低。在300 K时,ZT分别为:0.507（Zr Si₂N₄）、0.506（Ti Si₂N₄）及0.351（Hf Si₂N₄）。综上所述,本论文预测了四种具有室温高ZT的二维单层PtX₂,阐明了相关机理,还预测了二维单层YSi₂N₄的ZT,这些结果可为设计相关二维热电器件提供理论参考。更多还原

【Abstract】 In recent years,two-dimensional thermoelectric materials have attracted extensive research interest because of their advantages such as small size and light weight.Exploring novel two-dimensional thermoelectric materials with a room-temperature ZT that is greater than1.0 is an important subject in the field of thermoelectric ity.In this work,we study thermoelectric properties of two-dimensional monolayer PtX₂（X=O,S,Se,Te）and YSi₂N₄（Y=Ti,Zr,Hf）by using first-principles methods.The temperature-dependent ZT has been investigated,and high room-temperature ZT is obtained,while the underl ying mechanism is also clarified.The main results are presented below.Firstly,the band structure,phonon spectrum and thermoelectric properties of the four monolayer PtX₂ are calculated.These materials have stable structures,with indirect band gaps from 0.5 to 3.5 e V,based on the HSE06 exchange-correlation functional.Monolayer PtX₂ has a lower lattice thermal conductivity,ranging from 0.207 to 0.643 WK^-1M^-1,as compared to many other two dimensional materials.This leads to higher ZT at 300 K,which are 1.65（Pt Te₂）,1.42（P t S₂）,0.94（Pt O₂）and 0.84（Pt Se₂）,respectively.In addition,high ZT of 1.29（P t S₂）and 1.02（Pt Te₂）can still be obtained at 300 K when 1%tensile strain is applied to the lattice.These results indicate that the monolayer PtX₂ is a promising room-temperature thermoelectric material.Next,we study thermoelectric propterites of the monolayer YSi₂N₄.These materials have indirect bandgaps from 0.1 to 2.0 e V.Their lattice thermal conductivit y is about one order of magnitude larger than that of the monolayer PtX₂,and therefore leads to a less ZT at 300 K,which are 0.507（Zr Si₂N₄）,0.506（Ti Si₂N₄）and 0.351（Hf Si₂N₄）,respectively.In summary,we have predicted higher room-temperature ZT for the four monolayer PtX₂,and also predicted the room-temperature ZT for the monolayer YSi₂N₄.These results will give an insight into the design of two-dimensional thermoelectric devices.更多还原