Interface compatibility-induced quasi-volume-preserving martensitic phase transition in all-d-metal Co2NiT (T = Ti and V) Heusler compounds

Abstract

In this study, the quasi-volume-preserving martensitic phase transition in Co₂NiV and Co₂NiTi and the physical mechanism were theoretically investigated. Detailed studies revealed that the quasi-volume-conserving martensitic phase transformation originates from the compatible interface between austenite and martensite, which is also responsible for the experimentally observed non- or narrow-thermal-hysteresis phase transition. Consequently, the stressed interface due to incompatible geometric structure gives rise to an irreversible process and induces thermal hysteresis. In Co₂NiV and Co₂NiTi, the electron relaxation mechanism that drives the volume-conserving martensitic phase transition can be ascribed to lattice distortion and magnetism. As a result of electron relaxation, the interatomic electron-accumulating level was enhanced, which resulted in an increase in the covalent component in interatomic hybridization. The formation of the stronger chemical bonding stabilized the low-symmetric phases in Co₂NiV and Co₂NiTi. Moreover, the all-d-metal Heusler compounds Co₂NiV and Co₂NiTi were calculated to be ductile, which enabled them to work under more flexible conditions. Because the martensitic phase transition is metamagnetic, spontaneous magnetostriction can theoretically be expected in Co₂NiV and Co₂NiTi in a manner similar to that which affects invar alloy. The origin of quasi-volume-conserving martensitic phase transition and its physical mechanism is discussed to assist in the exploration of additional excellent materials for future applications.