摘要
四元锂-硫化合物具有较高的非线性光学(NLO)系数以及较宽的带隙,是一种具有较高应用潜力的非线性光学晶体。较高的热导率是非线性光学晶体综合性能的重要保障,可以保证非线性光学器件在实际应用中正常运行。然而,由于目前合成的四元锂-硫化合物的晶体尺寸通常较小,实验中难以测量其热导率,因此,采用第一性原理计算方法研究四元锂-硫化合物Li_(2)BaSnS_(4)的热导率,并通过与类似的三元硫化合物LiGaS_(2)进行对比,探讨其晶格热导率的微观来源。研究发现,Li_(2)BaSnS_(4)的晶格热导率较三元硫化合物LiGaS_(2)低,一方面是因为引入的Ba与S生成较弱的离子键,降低了声子群速度,另一方面是因为Ba的引入导致声子的非简谐效应增强。
Objective Infrared(3--5μm)lasers have various applications in the military and civilian areas.Nonlinear optical crystals are important in the field of infrared technology for implementing frequency conversion of the infrared laser.Recently,the synthetic and optical performance of quaternary lithium-sulfur compounds,Li_(2)XMS_(4)(X stands for Ba,Mn,and Cd;M stands for Ge and Sn)with tetrahedron units are widely researched because of their outstanding nonlinear optical coefficient and large energy gap.Besides,thermal conductivity is another important parameter to evaluate the performance of nonlinear optical crystals.High thermal conductivity will decrease the heat loss of crystals and keep the optical device working normally.However,the quaternary lithium-sulfur compounds and suitable crystal size are difficult to obtain experimentally,thus the thermal conductivity is difficult to measure.Theoretical predictions on the thermal transport behavior of quaternary lithium-sulfur compounds are imperative.In this study,the representative Li_(2)BaSnS_(4)is studied and compared with LiGaS_(2),to reveal the microcosmic influence factor of thermal conductivity.Methods Lattice thermal conductivity,which is caused by lattice vibration,is the main component of thermal conductivity.By solving the linearized phonon Boltzmann equation with the relaxation time approximated(RTA)method,the lattice thermal conductivity of Li_(2)BaSnS_(4)and LiGaS_(2)can be obtained.The phonon group velocity and lifetime play an important role in lattice thermal conductivity(Formula 1).Phonon lifetime is the representation of the phonon anharmonic effect.Phonon scattering rates are positive correlation with scattering intensity and the number of scattering channels,which are evaluated by Grüneisen parameters and weighted joint density of states(w-JDOS)(Formula 2).The harmonic and anharmonic phonon effects are calculated using PHONOPY and PHONO3PY programs combined with ab initio Simulation Package,which is based on density functional theory and proje
作者
梁国俊
李妍璐
魏磊
程秀凤
赵显
Liang Guojun;Li Yanlu;Wei Lei;Cheng Xiufeng;Zhao Xian(Institute of Crystal Materials,State Key Laboratory of Crystal Materials,Shandong University,Jinan,Shandong 250100,China;Advanced Materials Institute,Qilu University of Technology(Shandong Academy of Sciences),Jinan,Shandong 250014,China;Center for Optics Research and Engineering,Shandong University,Qingdao,Shandong 266237,China)
出处
《中国激光》
EI
CAS
CSCD
北大核心
2021年第12期278-286,共9页
Chinese Journal of Lasers
基金
国家自然科学基金(51902168)
山东省重点研发项目(2019JZZY010313)。
关键词
非线性光学
光学晶体
第一性原理
晶格热导率
声子群速度
非简谐效应
nonlinear optics
optical crystals
first principle
lattice thermal conductivity
phonon group velocity
anharmonic effect
