Extreme Poisson’s Ratio Of L1₂Phase Intermetallic Compounds From First-principles Study

Owing to its high symmetry, L1₂phase intermetallic compounds have theadvantages of good high-temperature resistance, creep resistance, wear resistance andoxidation-resistant. There are many studies about this structure. But they are notrelated to auxeticity. Auxetic material shows excellent mechanical properties and hashigh researching value. So far there has been little research on auxetic behavior ofmetal. And the study on the generation mechanism is more single. In this paper,extreme Poisson’s ratio of L1₂intermetallics has been systematically studied by usingfirst-principles method in terms of electronic structure. Moreover, this paperconstructed the SQS-32model of ternary Al₃Sc_1-xV_xtype intermetallic compoundsusing the ATAT package. And extreme Poisson’s ratio and its generating mechanismof these ternary intermetallics have been explored. The main work is as follows:（1） We have performed a systematic study on elastic constants for single crystals,related elastic modulus and extreme Poisson’s ratio for poly-crystals of102A3B-typeL1₂intermetallics using first-principles calculations. And the Relationship betweenextreme Poisson’s ratio and various factors haed been explored. The calculated resultsshowed all elastic constants of these structures obeyed the elastic stability criteria.31%of the investigated L1₂intermetallics has negative Poisson’s ratio. We also founda pronounced crrelation between the auxetic behaviour and anisotropy, elementcomposition of intermetallics, electronic work function. Furthermore, based on thedistribution of bonding charge densities, we revealed that the ductility and auxeticbehavior were attibutable to the directionality of bonds of these intermetallics. Thus,the electronic origin of the auxetic behavior in L1₂intermetallics can be interpreted asthe anisotropy of charge redistribution.（2） We have performed a systematic study on elastic constants for single crystals,related elastic modulus and extreme Poisson’s ratio for poly-crystals of Al₃Sc_1-xV_xintermetallic compounds using first-principles calculations. First, the analytical resultsof model error and formation enthalpy showed that these models are stable.Comparing with other papers, the results indicated that our results were reliability.The variation of various parameters of Al₃Sc_1-xV_xas a function of V content showedthat stability and auxeticity were validly improved by adding a certain amount ofternary alloying elements in the paper. Finally, the analysis result of Young’s modulusalong some orientations showed that ternary L1₂phase Al₃Sc_1-xV_xintermetallic compounds’ atoms connection form is same with binary L12phase intermetallics. Theauxetic behavior of ternary compounds was also attibutable to the directionality ofbonds of these intermetallics.