Simultaneous improvement of martensitic phase transition and ductility in Cu-doped and/or alloyed all-d-metal Ni2MnTa Heusler compounds

Ductile all-d-metal Heusler compounds with tunable martensitic phase transition are desirable for solid-state refrigeration applications. The theoretical investigations on martensitic phase transition and ductile characteristics of novel all-d-metal Ni2MnTa were conducted in this study. By introducing Cu atoms into Ni2MnTa, the improvement of martensitic phase transition and ductility was simultaneously realized. It was found that the substitution of Cu with more valence electrons for Ni, Mn, and Ta atoms resulted in an increase in metallic bonding. Owing to the enhanced metallic bonding, elastic moduli were softened, which improved shear deformation ability and contributed to tailoring the austenite phase stability. Hopefully, the anticipated martensitic phase transition can be tailored to an optimal temperature range. Moreover, the increased metallicity accounted for the simultaneously enhanced ductility. The enhanced metallic characteristics also resulted in contracting lattice sizes of Cu-doped and/or alloyed Ni2MnTa compounds due to the volume effect. Metallic bonding may be described as the mechanism for simultaneously controlling the phase stability and enhancing ductile properties in Cu-doped and/or alloyed Ni2MnTa compounds. The calculated energy, electronic structure, and elastic parameters further verified the occurrence of martensitic phase transition in Cu-doped and/or alloyed Ni2MnTa compounds. Current results suggest that chemical bonding could be employed as a significant tuning factor in the exploration of multipurpose Heusler compounds.