Mechanocaloric effects in Shape Memory Alloys

TL;DR

This paper reviews the giant mechanocaloric effects in shape memory alloys, highlighting differences between magnetic and non-magnetic types and their responses to stress and pressure.

Contribution

It provides a comprehensive survey of experimental data on elastocaloric and barocaloric effects in various shape memory alloys, clarifying their mechanisms.

Findings

Non-magnetic alloys show giant elastocaloric but negligible barocaloric effects.

Magnetic alloys exhibit both giant elastocaloric and barocaloric effects due to volume change.

Stress and pressure influence the phase transition differently in magnetic and non-magnetic alloys.

Abstract

Shape memory alloys are a class of ferroic materials which undergo a structural (martensitic) transition where the associated ferroic property is a lattice distortion (strain). The sensitiveness of the transition to the conjugated external field (stress), together with the latent heat of the transition gives rise to giant mechanocaloric effects. In non-magnetic shape memory alloys, the lattice distortion is mostly described by a pure shear and the martensitic transition in this family of alloys is strongly affected by uniaxial stress whereas it is basically insensitive to hydrostatic pressure. As a result, non-magnetic alloys exhibit giant elastocaloric effects but negligible barocaloric effects. By contrast, in a number of magnetic shape memory alloys, the lattice distortion at the martensitic transition involves a volume change in addition to the shear strain. Those alloys are affected by both uniaxial stress and hydrostatic pressure and they exhibit giant elastocaloric and barocaloric effects. The paper aims at providing a critical survey of available experimental data on elastocaloric and barocaloric effects in magnetic and non-magnetic shape memory alloys.