First-principles Calculation Of Calciumsilicon-carbon Ternary Compounds Under High Pressure

Under the effect of high pressure,the substance will change the structure,mechanical properties,optical properties,electrical properties.However,the shortcomings of long experiment cycles and high characterization requirements make the disadvantages of high-pressure experiments appear.At this time,in order to better explore the physical and chemical properties of substances under high pressure,computational material simulation methods are applied to high-pressure science.Based on previous research reports,we know that CaSi₂ in the Ca-Si binary system will exhibit superconductivity at 15 GPa,T_c=14 K;and?-SiC has high hardness,and it has also become the third candidate material for the third generation semiconductors;has excellent mechanical properties for the binary compound Ca-C,and is widely used in industrial production.From this,we are inspired to explore the high-pressure phase diagram of the ternary Ca-Si-C system.From previous experiments and theoretical work of the Ca-Si-C system,it was found that Ca element mainly enters SiC through adsorption and doping,and the addition of Ca element has a great influence on the electronic properties and magnetic properties of the system.In this paper,we pre-exploration of the ternary Ca-Si-C system and its properties,through CALYPSO based on particle swarm optimization algorithm and combining the first-principles simulation software package for the high-pressure phase of calcium silicon carbon ternary compound crystal structure prediction,the main work as follows:?1?we explored the structural phase transition of Ca-Si-C system in the pressure range of 0?400 GPa through the CALYPSO.We are concluded through calculation that,the phase transform sequence of CaSiC is C2/m-I?R3m?C2/m-II,CaSiC₂ is P2₁/m?C2/m?Pmma,for CaSi₂C is Cmc2₁?C2/m,and the sequence of phase transform of CaSi₂C₂ is P6₃/mmc?P6m2?P3m1?P2₁/m,their decomposition pressures is 220 GPa,250 GPa,170 GPa and150 GPa,respectively.These four components structures are stable in thermodynamics,kinetics and mechanics in the corresponding pressure range.?2?The calculation results of electronic properties show that the structures of CaSiC,CaSiC₂,CaSi₂C,and CaSi₂C₂ that exist stably under various pressures have metallic properties.Compared with?-SiC,the addition of Ca element reduces bulk modulus B,shear modulus G,Young's modulus Y and hardness.The comparison of the four component compounds shows that the C-C bond and Si-C bond have a greater influence on the mechanical properties of the structure.At the same time,the four-component calcium silicon carbon compounds are high hardness conductive materials at 10 GPa.