Interrelation between caloric characteristics and electronic / atomic structures in solid-state latent heat storage NiTi alloys

This study investigates the latent heat storage characteristics of equiatomic NiTi alloys by examining phase transition through both first-principles calculations and experimental observations. Changes in the density of states near the Fermi energy ( E f ) during the transition from the B2 to B19′ structure were identified as favorable for reducing electronic correlations, resulting in an energy difference of 0.1 eV and enhanced magnitude of latent heat ( η ). The antibonding states around E f are composed of 3d orbitals extending along specific directions in the B2 lattice, reflecting the significant difference in core potentials between Ni and Ti. In Nb-doped NiTi alloys subjected to pre-deformation, a decrease in η and the critical temperature was observed due to repeated transitions during thermal cycling. Additionally, the Pauli paramagnetic susceptibility (χ p ) increased in the B19′ phase. These effects arise from structural modifications in the B19’ phase induced by thermal cycling, rather than variations in the retained austenite volume.