摘要
基于嵌入原子法,本文给出了一个金属Ce原子间的相互作用势.利用该势分别计算了γ-Ce和α-Ce的晶格常数、结合能、弹性常数,计算结果与实验或第一性原理研究中得出的数值符合得较好.给出了两相Ce中如点缺陷形成能、表面能、层错能以及孪晶能等晶体缺陷形成能.通过分析两相Ce的声子谱,得出了不同温度下两相的晶格振动熵差,其中在室温条件下约为0.67kB/atom.还利用分子动力学模拟得出了该相变的等温线,并且利用径向分布函数分析了相变前后两相的晶体结构,确认了该相变为面心立方同构相变,即Ce的α-γ相变.由此表明,本文的嵌入原子法势,不仅可以分别合理地描述γ-Ce和α-Ce,还可以反映γ-Ce和α-Ce两相之间的相变.
Ce is a rare earth element in the periodic table.In the range of low temperature and low pressure,there are two face-centered-cubic(FCC)phases(α-Ce and γ-Ce)and a double-hexagonal-close-packed phase(β-Ce)for metallic Ce.At ambient temperature and about 0.7 GPa pressure,Ce undergoes γ→α phase transition with a volume shrink of 14%-17% discontinuously.In this paper,an embedded-atom method(EAM)potential compatible for α-Ce and γ-Ce was developed.This EAM potential has been employed to study several basic properties of cerium in these two FCC phases,such as equilibrium lattice constants,cohesive energies,and elastic constants.These results showed good accordance with experiments and first principle calculations.The lattice defects have been studied with the formation energy calculations of vacancies,interstitials,surfaces,stacking faults,and twinning defects in α-Ce and γ-Ce lattice.The lattice dynamics of α-Ce and γ-Ce have been analyzed using our EAM potential.The lattice vibrational entropy was calculated and plotted as functions of temperature for each phases.The vibrational entropy change across the α-γ phase transition showed to be ~0.67 kB per atom at ambient temperature.Using molecular dynamics simulation with our EAM potential,several isotherms and radial distribution functions were calculated.These isotherms and radial distribution functions demonstrate a first order phase transition between two FCC structures,corresponding to α-Ce and γ-Ce,with a critical point sets at T_c≈550 K and P_c≈1.21 GPa.Thus the newly developed EAM potential could provide a reasonable description of FCC Ce and its α-γ phase transition within the scale of classical molecular dynamics simulation.
作者
第伍旻杰
胡晓棉
Diwu Min-Jie;Hu Xiao-Mian(Graduate School, China Academy of Engineering Physics, Beijing 100088, China;National Laboratory of Computational Physics, Beijing Institute of Applied Physics and Computational Mathematics, Beijing 100088, China)
出处
《物理学报》
SCIE
EI
CAS
CSCD
北大核心
2019年第20期85-93,共9页
Acta Physica Sinica
关键词
原子间相互作用势
嵌入原子法
同构相变
铈
interatomic potential
embedded-atom method
isomorphic phase transition
cerium
