第一性原理研究Ba_(2)O_(2)S的结构、电子和热传输性质

First-principles Study on the Structural,Electronic and Thermal Properties of Ba_(2)O_(2)S

运用第一性原理和机器学习算法预测2种Ba_(2)O_(2)S结构,其具有P-3m1和P63/mmc空间群.通过弹性和声子特性计算发现2种结构都满足动力学和弹性稳定性要求.分析电子结构发现2种结构均为直接带隙半导体,带隙分别为4.6和4.5 eV,Ba—S和Ba—O键都是离子键型.B1-Ba_(2)O_(2)S和B2-Ba_(2)O_(2)S的晶格热导率表现出各向异性,[100]和[010]方向的热导率比[001]方向的晶格热导高约1.6倍.预测的2种结构的多晶热导率约为1.86和1.40 W·m^(-1)·K^(-1),因而Ba_(2)O_(2)S可以作为潜在的隔热材料.由于B1-Ba_(2)O_(2)S的群速度外积分值要高于B2-Ba_(2)O_(2)S,因此导致B1-Ba_(2)O_(2)S的热导率略高于B2-Ba_(2)O_(2)S.另外,2种结构声学模对热导率的贡献分别为73.4%和38.2%,光学模对热导率的贡献分别为26.6%和61.8%,B2-Ba_(2)O_(2)S的声光耦合强度大于B1-Ba_(2)O_(2)S.该研究有助于加强对低热导率材料Ba_(2)O_(2)S的结构、电子性质、力学性质和声学性质的认识.

Using the first principle method and machine learning algorithm,two structures of Ba_(2)O_(2)S with P-3m1 and P63/mmc space group are predicted.Through the elastic and phonon calculations,it is found that two structures meet the requirements of dynamics and elastic stability.The analysis of electronic structure shows that two structures are direct band gap semiconductors with two different band gaps of about 4.6 and 4.5 eV.Ba—S and Ba—O bonds are ionic bonds.The lattice thermal conductivity of B1-Ba_(2)O_(2)S and B2-Ba_(2)O_(2)S shows anisotropy,and thermal conductivity along the [100] and [010] directions is about 1.6 times higher than those in the [001] direction.The predicted polycrystalline thermal conductivity of the two structures is about 1.86 and 1.40 W·m^(-1)·K^(-1),respectively,so that Ba_(2)O_(2)S can be used as a potential thermal insulation material.Because the outer product integral for the group velocity of B1-Ba_(2)O_(2)S is higher than that of B1-Ba_(2)O_(2)S,the thermal conductivity of B1-Ba_(2)O_(2)S is higher than that of B2-Ba_(2)O_(2)S.In addition,the contributions of acoustic modes to the thermal conductivity of two structures are 73.4% and 38.2%,respectively,and the contributions of optical modes to the thermal conductivity are 26.6% and 61.8%,respectively.Moreover,the acousto-optic coupling strength of B2-Ba_(2)O_(2)S is greater than that of B1-Ba_(2)O_(2)S.This study will help to strengthen the understanding of the structure,electronic properties,mechanical properties and acoustic properties of Ba_(2)O_(2)S with a low thermal conductivity.