Physical Properties Of The Anti-perovskites RE₃AIC Using First-principles Calculations

The lattice constants,electronic structures,elastic constants andthermophysical properties of anti-perovskites RE3AlC(RE=Rear Earth)have been investigated by using first-principles calculations based on the density functional theory.The calculated lattice constants are in good agreement with the experimental value and other theoretical calculations except that of Yb3AlC.The bulk modulus,shear modulus,Young's modulus,Poisson's ratio and elastic anisotropic ratio are also evaluated from the calculated single crystal elastic constants.The calculated results indicate that Yb3AlC shows ductile behavior and the rest of RE3AlC are brittle manner according to the ratio of B/G and Pressure of Cauchy and Poisson's ratio.The results of band structure and density of states,indicate that the RE3AIC are metal.The bonding characteristics of RE3AIC are described as a mixture of covalent and ionic bonds.The anisotropy coefficient shows that Yb3AlC crystal structure is characterized by strong anisotropic elasticity and the most strenthening direction is[111]direction;the rest of the perovskite carbide RE3AlC show the weak elastic anisotropic,and the most stable solid direction is[100]direction.The micro-hardness value shows that hardness value of YbsAlC is the smallest,and that of Sc3AlC is the biggest.Based on the quasi-harmonic Debye model,Debye temperature,heat capacity,Gruneisen constant,thermal expansion coefficient and Gibbs free energy were calculated.The Debye temperature and the related thermodynamics properties of RE3AIC intermetallic compound vs the temperature and pressure variation were also obtained.For all RE3AIC intermetallic compound,the heat capacity,bulk modulus,thermal expansion coefficient,and Gibbs free energy vary with temperature and pressures similarly.The heat capacities increase quickly with the change of the temperature and pressure in the range from 0 K to 400 K;Debye temperature((?)D)increases with temperature.With increment of temperature and pressure,Gruneisen constant ?can be regarded as constant.The coefficients of thermal expansion increase quickly with increase of temperature,then which tends to a maximum.Gibbs free energy decreases with increase of temperature.Sc3AIC compound is the most stable,while Yb3AlC compounds is the most unstable.Bulk modulus B decreases with increase of temperature.