First-principles Study On The Structural And Electronic Properties Of SrCl₂ Under High Pressure

Pressure is one of the important parameters that determine the structure and properties of matter,it can effectively shorten the distance between atoms,cause the overlap of adjacent electron orbits,change the electron spin,and then regulate the electronic structure and the interaction between atoms,and induce under normal conditions.Induces new phenomena and new effects that cannot occur under conventional conditions,and generates high-pressure phases with new structures and new properties.High-pressure research can deepen people's understanding of the structure,properties and changing laws of matter,and is of great significance to the design of new functional materials and the understanding of planetary structure.Theoretically simulating the physical and chemical properties of materials can effectively shorten the experimental period and accelerate the research and development of new materials.It has become an important means for scientists to design new materials,greatly accelerating the progress of scientific research and industry.The fluorite structure is a cubic phase structure.The cations are arranged in the same way as the face-centered cubic structure,and the anions are filled in the tetrahedral gaps formed by the cations.SrCl₂is the only crystal with cubic fluorite structure among divalent alkaline earth metal chlorides,and is considered to have the same pressure-induced phase transition behavior as alkaline earth metal difluorides with fluorite structure.However,the difference in the atomic radius and electronegativity of fluorine and chlorine atoms will cause the alkaline earth metal difluoride and dichloride to form completely different new structures under high pressure,which have novel physical and chemical properties.The high-pressure phase study of SrCl₂ is helpful to understand the pressure-induced phase transition and evolution of alkaline earth metal dichlorides.In this paper,the CALYPSO structure search software independently developed by the research group was used to conduct research on the high-pressure structure phase transition,dynamic stability,electronic properties of SrCl₂,and the following results were achieved:1.The CALYPSO method was used to systematically search the high-pressure phase of SrCl₂ under 0-300GPa,and two new high pressure phases of SrCl₂ with space group symmetry of Cmcm and I4/mmm were proposed.The rare dodecahedral structure unit of SrCl₁₀ appeared in the two new high pressure phases.2.The new high-pressure phase transition sequence of SrCl₂ is determined:the fluorite structure(Fm-3m)under normal pressure is transformed into a Pb Cl₂-type structure(Pnma)at 4.6 GPa,and finally into a Cmcm structure at 106 GPa.This phase transition sequence broke the cognition of the high-pressure behavior of SrCl2 in previous studies.3.Through the calculation of the electronic structure,it is found that the two predicted high-voltage phases are both semiconductors,and the atoms are combined through ionic bonds.With the increase of pressure,the band gap of Cmcm phase shows an interesting phenomenon that it first increases,then decreases and finally closes.