Giant elastocaloric effect and exceptional mechanical properties in an all-d-metal Ni-Mn-Ti alloy: Experimental and ab-initio studies

Exploring novel materials with superior elastocaloric effect (eCE) is a central issue for the development of eCE refrigeration technique. In this work, we report a giant adiabatic temperature change Delta T-ad of -20.4 K in the < 100 >-textured all-d-metal Ni50Mn31.75Ti18.25 bulk alloy. The Delta T-ad value, comparable to that of the sate-of-the-art Ni-Ti alloys, surpasses the existing conventional Ni-Mn-based alloys. Investigations show that the giant Delta T-ad is attributed to the large lattice volume change during martensitic transformation and the negligible negative contribution of magnetic entropy change owing to its weak magnetism. By performing X-ray diffraction measurements and ab-initio calculations, the weak magnetism is found to be intrinsically related to the B2 ordered structure in which the magnetic moments of the antiferromagnetically coupled Mn atoms located at 4a and 4b sites are cancelled out each other. Both experimental and theoretical studies confirmthat Ni-Mn-Ti alloys possess the significantly enhanced mechanical properties compared with the conventional Ni-Mn-based alloys. Electronic structure investigations reveal that this could be ascribed to the replacement of d-d interaction for the strongly covalent p-d hybridization. Outstanding elastocaloric effect of the all-d-metal alloy opens a door for searching novel promising materials used as the elastocaloric refrigerants. (c) 2019 The Authors. Published by Elsevier Ltd.