First Principles Study Of Co-based Heusler Alloy

Researchers are constantly exploring to meet the needs of the new electronic industry.Among numerous new functional materials,Heusler alloys also occupy a place and are widely concerned for their excellent physical properties,which are particularly important for further research on Heusler alloys.Among them,Co based Heusler alloy has good physical properties in this system,in order to study the influence of the same host group elements on Co based Heusler alloy.Therefore,this paper selects Co₂XY（X=Ti,Zr,Y=Al,Ga,In,Sn）all Heusler alloy and Co Zr Z（Z=As,Bi,Sb）half Heusler alloy,and adopts the first principle calculation based on density functional theory（DFT）to study the crystal structure and properties,electronic structure,mechanical properties,and thermodynamic properties of Co₂XY（X=Ti,Zr,Y=Al,Ga,In,Sn）all Heusler alloy and Co Zr Z（Z=As,Bi,Sb）half Heusler alloy.The main tasks are as follows:（1）The cohesive energy and enthalpy of formation of Co₂XY（X=Ti,Zr,Y=Al,Ga,In,Sn）Full-Heusler alloy indicate that Co₂Ti Al has the best thermodynamic stability,while Co₂Ti In and Co₂Zr In have poor thermodynamic stability.According to the mechanical Stability criterion,it can be concluded that Co₂Zr Al and Co₂Zr Ga do not meet the mechanical stability criterion of cubic structure,while the other six all Heusler alloys meet.According to the TDOS distribution,it is indicated that eight Co₂XY Heusler alloys exhibit metallic behavior,and their contributions to TDOS mainly come from the Co-d,X-d,and Y-p,d states.By analyzing the bulk modulus,shear modulus,Young’s modulus,B/G,v,and hardness,it was found that all six full-Heusler alloys are ductile materials.And based on the analysis of elastic anisotropy,their bulk modulus is isotropic,while shear modulus and Young’s modulus are anisotropic,with varying degrees of anisotropy.（2）The cohesive energy and formation enthalpy of Co Zr Z（Z=As,Bi,Sb）Half-Heusler alloy have been studied,indicating that these three substances are stable.According to the mechanical stability criterion,it is found that Co Zr Z（Z=As,Bi,and Sb）Half-Heusler alloys all meet the mechanical stability criterion for cubic structures.The study of electronic structure shows that these three semi-Heusler alloys have metallic behavior.The contributions to TDOS mainly come from Co-d,Zr-d,and Z-p,d states.Co-Zr-Z can form strong chemical bonds,enabling the material to remain stable.The analysis of mechanical properties indicates that these three Heusler alloys are all ductile materials.The study of its elastic anisotropy shows that Co Zr Bi>Co Zr As>Co Zr Sb.（3）For the above two systems of Heusler alloy C_V,both follow the Duron Petit law.The trend of C_V and C_P is roughly the same,both rapidly increasing with temperature at low temperatures.When reaching high temperatures,the trend slows down with temperature rise.Heusler alloy has higher coefficient of thermal expansion at lower pressure and higher temperature.By analyzing the Grüneisen constantγanalysis,the decrease is rapid during the change process from 0GPa to10GPa.As the pressure increases,the decline gradually slowed down.By calculating the speed of sound,it was found that the higher the density of the material,the slower the speed.Research on thermal conductivity has found that thermal conductivity is closely related to Debye temperature.Lower Debye temperature corresponds to lower thermal conductivity,while higher Debye temperature corresponds to higher thermal conductivity.The three-dimensional diagram of thermal conductivity indicates that the thermal conductivity of both systems is anisotropic.