Theoretical Study On Martensite Transformation And Elastic Constants Of Co₂VZ(Z=Ga,Si) Magnetic Shape Memory Alloy

Calculating and studying the phase stability and elastic constant under different magnetic order is of great significance to the experimental design of Co₂VZ(Z=Ga,Si)magnetic shape memory alloy with good performance.In this paper,the precise Muffin-Tin orbit combined with the coherence potential approximation method is used.First,the lattice structure,magnetic moment,and elasticity of the cubic L2₁phase and the tetragonal D0₂₂phase of the Co₂VZ(Z=Ga,Si)stoichiometric alloy at 0 K are calculated systematically Constants,electronic structure and total energy;secondly,the lattice structure,magnetic moment,elastic constant and total electronic energy of the cubic austenite phase of the Co₂V(Ga Si)quaternary disordered alloy are calculated.The research results show that in the FM state,the Co₂VGa alloy has an L2₁cubic stable structure.When the magnetic disorder"y?0.2",the system undergoes a martensitic transformation and has a D0₂₂tetragonal structure;whether in the FM or PM state,All Co₂VSi alloys can undergo martensitic transformation,and the D0₂₂phase will become more and more stable relative to the parent phase as the degree of magnetic disorder increases;for the Co₂VGa_1-xSi_xdisordered alloy,when x=0.2?0.8,it has L2₁Cubic stable structure;when"x?0.9",martensitic transformation can occur,with D0₂₂tetragonal stable structure.The total magnetic moment of Co₂VGa and Co₂VSi alloys is mainly due to the contribution of Co atoms,and V atoms only contribute a small part;their total magnetic moment corresponding to the L2₁phase is much greater than the value of the D0₂₂phase,which leads to the magnetic excitation process from FM to PM.The electron energy is always lower and lower.For the Co₂VGa_1-xSi_xdisordered alloy,the total magnetic moment is also mainly derived from the contribution of Co and V atoms,while the contribution of Ga and Si atoms is negligible.Compared with Co₂VGa,the tetragonal shear elastic constant C'((C₁₁-C₁₂)/2)value of Co₂VSi alloy is smaller in FM and PM states,so it is more prone to martensitic transformation;when the alloy is magnetic When the properties are changed from ferromagnetic FM state to paramagnetic PM state,the tetragonal shear elastic constant C'value of the two ordered alloys of Co₂VGa and Co₂VSi becomes smaller,which also shows that the magnetic disorder model is beneficial to the deformation of the tetragonal lattice structure.For the Co₂VGa_1-xSi_xalloy,with the increase of the component x,the tetragonal shear elastic constant C'value becomes smaller and smaller,the stability of the L2₁phase becomes worse and worse,and the tetragonal lattice deformation is more and more likely to occur.According to the Jahn-Teller instability effect,the calculated electronic density of states can well explain the relative stability of the L2₁and D0₂₂phases of the Co₂VGa and Co₂VSi alloys in the two magnetic states.It is hoped that the theoretical results can provide an effective reference for the experimental study of Co₂VZ(Z=Ga,Si)alloys with excellent properties.