Detailed structural,mechanical,and electronic study of five structures for CaF2 under high pressure  

作　　者：Ying Guo Yumeng Fang Jun Li 郭颖;方钰萌;李俊(Jiangsu Collaborative Innovation Center of Atmospheric Environment and Equipment Technology,Jiangsu Key Laboratory of Big Data Analysis Technology,Nanjing University of Information Science and Technology,Nanjing 210044,China;Mingde New Material Technology Co.,LTD,Anji 313300,China)

机构地区：[1]Jiangsu Collaborative Innovation Center of Atmospheric Environment and Equipment Technology,Jiangsu Key Laboratory of Big Data Analysis Technology,Nanjing University of Information Science and Technology,Nanjing 210044,China [2]Mingde New Material Technology Co.,LTD,Anji 313300,China

出　　处：《Chinese Physics B》2021年第3期194-204,共11页中国物理B（英文版）

基　　金：Project supported by the National Natural Science Foundation of China(Grant No.61971229).

摘　　要：Detailed density functional theory(DFT)calculations of the structural,mechanical,thermodynamic,and electronicproperties of crystalline CaF2 with five different structures in the pressure range of 0 GPa–150 GPa are performed byboth GGA(generalized gradient approximation)-PBE(Perdew–Burke–Ernzerhof)and LDA(local density approximation)-CAPZ(Cambridge Serial Total Energy Package).It is found that the enthalpy differences imply that the fluorite phase→PbCl2-type phase→Ni2In-type phase transition in CaF2 occurs at PGGA1=8.0 GPa,PGGA2=111.4 GPa by usingthe XC of GGA,and PLDA1=4.5 GPa,PLDA2=101.7 GPa by LDA,respectively,which is consistent with previousexperiments and theoretical conclusions.Moreover,the enthalpy differences between PbCl2-type and Ni2In-type phases inone molecular formula become very small at the pressure of about 100 GPa,indicating the possibility of coexistence of twophase at high pressures.This may be the reason why the transition pressure of the second phase transition in other reportsis so huge(68 GPa–278 GPa).The volume changed in the second phase transition are also consistent with the enthalpydifference result.Besides,the pressure dependence of mechanical and thermodynamic properties of CaF2 is studied.Itis found that the high-pressure phase of Ni2In-type structure has better stiffness in CaF2 crystal,and the hardness of thematerial has hardly changed in the second phase transition.Finally,the electronic structure of CaF2 is also analyzed withthe change of pressure.By analyzing the band gap and density of states,the large band gap indicates the CaF2 crystal isalways an insulator at 0 GPa–150 GPa.

关 键 词：density functional theory(DFT) high-pressure phase transition COEXISTENCE 

分 类 号：O472[理学—半导体物理]