Prediction And Theoretical Study Of Ag-based New Heusler Alloys

In the more than one hundred years since the advent of Heusler alloy,a large number of new Heusler alloy materials with various physical properties have been continuously discovered,synthesized and widely used,making the design and synthesis of new Heusler functional materials still one of the hot research directions in the field of materials science.We used the first-principles calculations method based on density functional theory to perform high-throughput calculations on Ag-based Heusler alloy materials obtained by atomic substitution,and obtained a variety of stable new Heusler alloy structures.The paper systematically discusses the stability of these new structures,and also studies their structural properties,mechanical properties,and electronic properties,which provide a theoretical basis for the experimental synthesis and the research of other new spin-effect materials.The main results of this paper are as follows:1.The general chemical formula of the full Heusler alloy is X₂YZ.We use Agas the X atom,transition metal element Scas the Y atom,and Ge as the Z atom to construct Ag₂ScGe structures of L2₁ and XA respectively.Through structural optimization,we obtained the ideal lattice constants of the two structures,and discussed the stability of the structure.The results show that the Ag₂ScGe structure of XA configuration is stable.A high-pressure stability study of Ag₂ScGe in the XA configuration of this stable structure shows that this structure is stable under a high pressure of at least 50 GPa.The calculation of its mechanical properties and electronic properties shows that it has a large Poisson’s ratio and B/G value,and the energy band intersects the Fermi level,which indicates that this new type of Heusler alloy structure Ag₂ScGe is a kind of good ductility Metallic materials.2.After atomic replacement of Ag₂ScGe,the proven stable XA configuration Heusler alloy structure,we obtained a batch of initial structures Ag₂YGa（Y=Sc,Ti,V,Cr,Mn,Fe,Co,Ni）.The fully optimized phonon spectrum of these structures shows that only the Ag2Ti Ga structure and the Ag₂VGa structure are dynamically stable.Combined with the study of mechanical stability,it shows that these two structures are stable structures.We have also studied and compared other mechanical properties and electronic properties of these two structures.From the point of view of B/G value,Ag₂VGa and Ag₂Ti Ga structures are ductile materials,and the ductility of Ag₂Ti Ga structure is greater than that of Ag₂VGa structure.According to the study of the electronic properties of the two structures,there is no spin band gap in their spin bands,which indicates that the Ag₂Ti Ga structure and the Ag₂VGa structure are both metallic materials,and the spin-state density diagram of the Ag₂VGa structure is in There is obvious spin split near the Fermi level,and the calculated total magnetic moment of the Ag₂VGa structure is 2.28μB,which indicates that Ag₂VGa has good magnetism.3.By substituting the Scatoms and Ge atoms of the Ag₂ScGe structure,a number of structures Ag₂YTl（Y=Sc,Ti,V,Cr,Mn,Fe,Co,Ni）are obtained.The phonon dispersions of these optimized structures show that only Ag₂Ti Tl is dynamically stable.After that,we also replace the atoms in Ag₂VGa and Ag₂Til structures respectively,and obtained four structures,AgTiVGa,AgVTi Ga,AgTiVTl and AgVTi Tl,whose optimized phonon spectra show that only AgTiVGa structure is dynamically stable.We have also studied mechanical properties and electronic properties of Ag₂Ti Tl and AgTiVGa.From the perspective of bulk modulus,shear modulus,Young’s modulus and Poisson’s ratio,the compression resistance,shear resistance,stiffness,and ductility of Ag₂Ti Tl are all greater than that of AgTiVGa,and both Ag₂Ti Tl and AgTiVGa have great ductility and elasticity of the anisotropy.The calculated electronic properties of the two structures show that both Ag₂Ti Ti and AgTiVGa are metallic materials.Besides,the calculated spin energy band and spin state density of the AgTiVGa have very obvious spin splitting and the calculated total magnetic moment of the AgTiVGa is 4.79μB,which suggest that it has good magnetic properties.Combined with the calculated atomic density of states and atomic magnetism,it can be known that the magnetic properties of AgTiVGa mainly come from Ti atoms and V atoms.These results indicate that both Ag₂Ti Tl and AgTiVGa are well-ductile metallic materials,and AgTiVGa is also a magnetic material.