Study On Physical Properties Of The Antiperovskite Compounds And The Doped Antiperovskite Compounds

In recent years,antiperovskite compounds have attracted wide attention due to their unique and remarkable properties,which are well used in many fields,such as magnetic recording materials,optical radiation devices and anti-ultraviolet materials.In order to further study the potential applications of antiperovskites in the fields of magnetism and optics,it is necessary to study and elaborate their physical properties.So far,there are relatively few studies on the physical properties of metal antiperovskites Mn₃XN（X=Ni,Pd,Pt）and semiconductor antiperovskites Mg₃XN（X=P,As,Bi,Sb）under different conditions.Therefore,in this thesis,their physical properties are investigated based on the first principle.The main contents are as follows:For the metallic antiperovskites Mn₃XN（X=Ni,Pd,Pt）,the thermodynamic stability,electronic,mechanical,anisotropy,magnetic,thermodynamic properties and other physical properties of the three compounds are investigated.It is found that all Mn₃XN compounds exhibit magnetism,and their magnetism mainly comes from the contribution of Mn atoms.Meanwhile,the results of their elastic modulus are also given,where the bulk modulus and shear modulus of Mn₃Pt N are larger than those of Mn₃Pd N and Mn₃Ni N.The results of the universal isotropic constant and the figure of three-dimensional Young’s modulus confirm that Mn₃Pd N may be potentially isotropic material,while Mn₃Ni N has the most pronounced anisotropy.The Debye temperatures of Mn₃Ni N,Mn₃Pd N and Mn₃Pt N are further obtained by their sound velocities in different directions.In addition,the critical pressures of magnetic transition for the three compounds are given in the thesis.In terms of thermodynamic properties,Gibbs2 code is used to study Debye temperature,entropy and specific heat.The above studies provide theoretical references for their applications in the fields of magnetism and thermodynamics.For the semiconductor antiperovskite Mg₃XN（X=P,As,Sb,Bi）,the thermodynamic stability,electronic,mechanical,anisotropy and optical properties of the four compounds are investigated.The results show that Mg₃XN compounds are all direct band-gap semiconductors.In the optical properties,their complex dielectric function,extinction coefficient,absorption rate and so on are studied.The results of elastic parameters show that Mg₃PN has the largest bulk modulus and shear modulus.The Debye temperature is obtained by studying the sound velocity in different directions.By introducing high pressure,the deformation and elastic modulus of the compound are further explained with the change of pressure,which provides a theoretical reference for the application of materials under high pressure.In addition,by doping the Mn element into the Mg₃XN compound to introduce magnetism into the system,the chemical formula of Mg₃XN compound is updated to Mg_2.5Mn_0.5XN.The results of the enthalpy of formation indicate that the doped compound is stable.Then the magnetic moments and total magnetic moments of different atoms are given.The possibility of Mg₃XN compound as photovoltaic material and Mn-doped magnetic mechanical material is verified.