Elastocaloric Effect Associated with the Martensitic Transition in Shape-Memory Alloys

Abstract

The elastocaloric effect in the vicinity of the martensitic transition of a Cu-Zn-Al single crystal has been studied by inducing the transition by strain or stress measurements. While transition trajectories show significant differences, the entropy change associated with the whole transformation (S t ) is coincident in both kinds of experiments since entropy production is small compared to S t . The values agree with estimations based on the Clausius-Clapeyron equation. The possibility of using these materials for mechanical refrigeration is also discussed. DOI: 10.1103/PhysRevLett.100.125901 PACS numbers: 65.40.Gÿ, 75.30.Sg, 81.30.Kf Caloric effects are expected to occur under the application of an external field to a given material. The elastocaloric effect [1] is the mechanical analogue of the magnetocaloric effect that has received considerable attention in the recent years owing to its potential use for environmentally friendly refrigeration [2]. The magnetocaloric effect is related to the isothermal change of entropy or the adiabatic change of temperature that takes place within a material when a magnetic field is applied or removed. This effect originates from the coupling between the magnetic sublattice and an externally applied magnetic field and thus occurs in any magnetic material. A large effect is expected in the vicinity of field-induced, firstorder phase transitions where large entropy changes should occur [3]. By analogy, the elastocaloric effect is defined as the isothermal change of entropy or the adiabatic change of temperature that takes place when a mechanical field (stress) is applied or released in a given material. Indeed, this effect is expected to be a consequence of the coupling between an external applied stress and the lattice. Continuing with the analogy, a large elastocaloric effect is also foreseen in systems undergoing stress-induced, first-order phase transitions. Good candidates to show this effect are shape-memory alloys. These materials undergo a diffusionless purely structural transition from a cubic to a lower symmetry phase that can be stress induced [4]. Actually, shape-memory properties are related to this transition and refer to the ability of these systems to remember their original shape after severe deformation [5].In contrast to magnetism, instead of controlling the applied stress (or force) which is the variable thermodynamically equivalent to the magnetic field, in mechanical experiments, the system is usually driven by controlling the strain (generalized displacement) which is the conjugated variable to the stress in the way that magnetization is the conjugated variable of the magnetic field. In magnetic systems, due to the difficulty in controlling magnetization, magnetization-driven experiments aimed at studying the magnetocaloric effect have not, to our knowledge, been reported. Thus, comparing results from both field-or stress-driven and magnetization or strain-driven experiments is of general interest since constraining the (generalized) displacement pr...

Multicaloric effect in ferroelectric PbTiO3from first principles

“…Contrary to the old belief that such effects, while common, are miniscule, a large variety of giant caloric effects has been recently discovered in some ferroic materials [1][2][3][4][5][6][7][8][9][10] . These discoveries have opened the door to the use of these giant effects in an efficient and environmentally friendly solid-state refrigeration technology.…”

“…Note that this effect is also termed elastocaloric effect 5 . A normal tensile stress field, σ, acting on the plane perpendicular to the [001] direction (polarization direction in ferroelectric phase) and ranging from 0 up to 2 GPa was applied to and subsequently removed from the simulated sample using the direct approach as outlined in Ref.…”

“…As a result, it was long believed that the effect is miniscule by its very nature 15 and very little effort was directed towards its understanding, or a search of materials with large caloric effects. There has been a drastic change in the situation, however, in the recent years, thanks to the discoveries of giant magnetocaloric effect 1,2,9 , giant electectrocaloric effect 3,4,6,10 , followed by the reports of giant elastocaloric and barocaloric effects 5,7,8,16 . However, except for the Refs.…”

“…Moreover, given a relative abundance of extrinsic multiferroics among ferroics with multiple order parameters, such prediction may open an unusual route to solid state refrigeration advancement. Recent discoveries of giant caloric effects in some ferroic materials [1][2][3][4][5][6][7][8][9][10] have opened the door to the use of solidstate materials as an alternative to gases for conventional and cryogenic refrigeration 11 . The wide class of ferroics includes such diverse materials as ferromagnets and magnetic materials, ferroelectrics, ferroelastics and multiferroics.…”

Inverse barocaloric effect in the giant magnetocaloric La–Fe–Si–Co compound

“…Th e tuning parameter for the caloric eff ect (external fi eld) can be any generalized thermodynamic force, provided that the change in the conjugated generalized thermodynamic displacement is large enough. Hence, giant caloric eff ects have already been reported for magnetic fi eld (magnetocaloric eff ect) 1 -3 , electric fi eld (electrocaloric eff ect) 4,5 , uniaxial stress (elastocaloric eff ect) 6 and hydrostatic pressure (barocaloric eff ect) 7,8 .…”