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 Delta V/V-0 upon the martensitic transformation. Using the Ni50Mn50 binary alloy as the prototype, a large transformation entropy change Delta S-tr can be tailored in the vicinity of room temperature by simultaneously doping Cu and Ga. Especially, the vertical bar Delta S-tr vertical bar 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 Delta V/V-0 values, i.e., 1.81 and 1.82%, respectively. Such enhanced Delta S-tr values thus yield giant Delta T-ad 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 (vertical bar Delta T-ad/Delta sigma(max)vertical bar) 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.

Automated summary

In this study, a strategy to achieve a giant elastocaloric response by enlarging the lattice volume change was presented, resulting in Ni-Cu-Mn-Ga alloys with tailored transformation entropy change. These alloys showed significantly large temperature changes of up to -23.5 and -19.3 K upon removing compressive stress, indicating potential for high-performance elastocaloric materials.