Giant Elastocaloric Effect in Ni-Mn-Ga-Based Alloys Boosted by a Large Lattice Volume Change upon the Martensitic Transformation.

High-performance elastocaloric materials are highly sought in developing energy-efficient and environmentally friendly solid-state elastocaloric refrigeration. Here, we present an effective strategy to achieve a giant elastocaloric response by enlarging the lattice volume change ΔV/V0 upon the martensitic transformation. Using the Ni50Mn50 binary alloy as the prototype, a large transformation entropy change ΔStr can be tailored in the vicinity of room temperature by simultaneously doping Cu and Ga. Especially, the |ΔStr| values in the ⟨001⟩A-textured Ni30Cu20Mn39.5Ga10.5 and Ni30Cu20Mn39Ga11 alloys prepared by directional solidification can be as large as 47.5 and 46.7 Jkg-1 K-1, respectively, due to the significant ΔV/V0 values, i.e., 1.81 and 1.82%, respectively. Such enhanced ΔStr values thus yield giant ΔTad values of up to -23.5 and -19.3 K on removing the compressive stress in these two alloys, being much higher than those in Heusler-type alloys reported previously. Moreover, owing to the relatively low driving stress endowed by the highly textured microstructure, the specific adiabatic temperature change (|ΔTad/Δσmax|) in the present work can be as large as 77.2 K/GPa. This work is expected to provide new routes in designing high-performance elastocaloric materials with the combination of a giant elastocaloric response and low driving stress.