Giant barocaloric effect in all-d-metal Heusler shape memory alloys

We have studied the barocaloric properties associated with the martensitic transition of a shape memory Heulser alloy Ni50Mn31.5Ti18.5 which is composed of all-d-metal elements. The composition of the sample has been tailored to avoid long range ferromagnetic order in both ausenite and martensite. The lack of ferromagnetism results in a weak magnetic contribution to the total entropy change thereby leading to a large transition entropy change. The combination of such a large entropy change and a relatively large volume change at the martensitic transition gives rise to giant barocaloric properties in this alloy. When compared to other shape memory Heusler alloys, our material exhibits values for adiabatic temperature and isothermal entropy changes significantly larger than values reported so far for this class of materials. Furthermore, our Ni50Mn31.5Ti18.5 also compares favourably to the best state-of-the-art magnetic barocaloric materials.Peer ReviewedPostprint (author's final draft

Tailoring barocaloric and magnetocaloric properties in low-hysteresis magnetic shape memory alloys

We report on the barocaloric and magnetocaloric effects in a series of low-hysteresis Ni-Mn-In magnetic shape memory alloys. We show that the behaviour exhibited by several quantities that characterise these caloric effects (isothermal entropy change, adiabatic temperature change and refrigerant capacity) can be rationalised in terms of the relative distance between the Curie point of the austenite and the martensitic transition temperature. It is found that the two caloric effects exhibit opposite trends. The behaviour of the barocaloric effect parallels that exhibited by the transition entropy change, thereby showing larger values for weakly magnetic samples. Regarding the magnetocaloric effect, the isothermal entropy change is maximum for those samples transforming martensitically close to the Curie point of the austenite. Such a maximum value does not correspond to the maximum adiabatic temperature change, and samples with martensitic transition slightly below the Curie point do have larger temperature changes as a result of the strongest sensitivity of the transition to the magnetic field. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.Postprint (author's final draft

Reversible adiabatic temperature changes at the magnetocaloric and barocaloric effects in Fe49Rh51

We report on the adiabatic temperature changes (Delta T) associated with the magnetocaloric and barocaloric effects in a Fe49Rh51 alloy, For the magnetocaloric effect, data derived from entropy curves are compared to direct thermometry measurements. The agreement between the two sets of data provides support to the estimation of Delta T for the barocaloric effect, which are indirectly determined from entropy curves. Large Delta T values are obtained at relatively low values of magnetic field (2 T) and hydrostatic pressure (2.5 kbar), It is also shown that both magnetocaloric and barocaloric effects exhibit good reproducibility upon magnetic field and hydrostatic pressure cycling, over a considerable temperature range. (C) 2015 AIP Publishing LL

Reversible and irreversible colossal barocaloric effects in plastic crystals

The extremely large latent heat exchanged in phase transitions involving strong molecular orientational disordering has recently led to the proposal of plastic crystals as a feasible solution for solid-state barocaloric eco-friendly cooling technologies. Here we determine the reversible barocaloric response of four plastic crystals derived from neopentane [C(CH3)4]: (NH2)C(CH2OH)3 (TRIS for short), (NH2)(CH3) C(CH2OH)2 (AMP), (CH3)C(CH2OH)3 (PG) and (CH3)3C(CH2OH) (NPA). All of them display colossal entropy changes at their ordered-plastic phase transition, which is a primal requirement for competitive barocaloric materials. However, we show that it is also important to verify that the large barocaloric effects can be achieved using pressures that, while being moderate, are large enough to overcome the pressure-dependent hysteresis. From this quantity and using the quasi-direct method, we determine the minimum pressure needed to achieve reversible barocaloric effects, prev, for each compound. Specifically, we find a small and moderate prev for PG and NPA, respectively, which therefore display colossal reversible barocaloric effects comparable to harmful fluids used in current refrigerators and thus confirm the potential of plastic crystals as excellent alternatives. Instead, in TRIS and AMP, the obtained prev is excessive to yield reversible barocaloric effects useful for cyclic applications.Peer Reviewe

Giant barocaloric effects over a wide temperature range in the superionic conductor AgI

Current interest in barocaloric effects has been stimulated by the discovery that these pressure-driven thermal changes can be giant near ferroic phase transitions in materials that display magnetic or electrical order. Here we demonstrate giant inverse barocaloric effects in the solid electrolyte AgI, near its superionic phase transition at ~420 K. Over a wide range of temperatures, hydrostatic pressure changes of 2.5 kbar yield large and reversible barocaloric effects, resulting in large values of refrigerant capacity. Moreover, the peak values of isothermal entropy change (60 J K-1 kg-1 or 0.34 J K-1 cm-3) and adiabatic temperature changes (18 K), which we identify for a starting temperature of 390 K, exceed all values previously recorded for barocaloric materials. Our work should therefore inspire the study of barocaloric effects in a wide range of solid electrolytes, as well as the parallel development of cooling devices.Peer Reviewe

Giant barocaloric effect in all-d-metal Heusler shape memory alloys

We have studied the barocaloric properties associated with the martensitic transition of a shape memory Heulser alloy Ni50Mn31.5Ti18.5 which is composed of all-d-metal elements. The composition of the sample has been tailored to avoid long range ferromagnetic order in both ausenite and martensite. The lack of ferromagnetism results in a weak magnetic contribution to the total entropy change thereby leading to a large transition entropy change. The combination of such a large entropy change and a relatively large volume change at the martensitic transition gives rise to giant barocaloric properties in this alloy. When compared to other shape memory Heusler alloys, our material exhibits values for adiabatic temperature and isothermal entropy changes significantly larger than values reported so far for this class of materials. Furthermore, our Ni50Mn31.5Ti18.5 also compares favourably to the best state-of-the-art magnetic barocaloric materials.Peer Reviewe

Giant barocaloric effects at low pressure in ferrielectric ammonium sulphate

Caloric effects are currently under intense study due to the prospect of environment-friendly cooling applications. Most of the research is centred on large magnetocaloric effects and large electrocaloric effects, but the former require large magnetic fields that are challenging to generate economically and the latter require large electric fields that can only be applied without breakdown in thin samples. Here we use small changes in hydrostatic pressure to drive giant inverse barocaloric effects near the ferrielectric phase transition in ammonium sulphate. We find barocaloric effects and strengths that exceed those previously observed near magnetostructural phase transitions in magnetic materials. Our findings should therefore inspire the discovery of giant barocaloric effects in a wide range of unexplored ferroelectric materials, ultimately leading to barocaloric cooling devices

Tailoring barocaloric and magnetocaloric properties in low-hysteresis magnetic shape memory alloys

We report on the barocaloric and magnetocaloric effects in a series of low-hysteresis Ni-Mn-In magnetic shape memory alloys. We show that the behaviour exhibited by several quantities that characterise these caloric effects (isothermal entropy change, adiabatic temperature change and refrigerant capacity) can be rationalised in terms of the relative distance between the Curie point of the austenite and the martensitic transition temperature. It is found that the two caloric effects exhibit opposite trends. The behaviour of the barocaloric effect parallels that exhibited by the transition entropy change, thereby showing larger values for weakly magnetic samples. Regarding the magnetocaloric effect, the isothermal entropy change is maximum for those samples transforming martensitically close to the Curie point of the austenite. Such a maximum value does not correspond to the maximum adiabatic temperature change, and samples with martensitic transition slightly below the Curie point do have larger temperature changes as a result of the strongest sensitivity of the transition to the magnetic field. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

Colossal barocaloric effects near room temperature in plastic crystals of neopentylglycol

There is currently great interest in replacing the harmful volatile hydrofluorocarbon fluids used in refrigeration and air-conditioning with solid materials that display magnetocaloric, electrocaloric or mechanocaloric effects. However, the field-driven thermal changes in all of these caloric materials fall short with respect to their fluid counterparts. Here we show that plastic crystals of neopentylglycol (CH3)2C(CH2OH)2 display extremely large pressuredriven thermal changes near room temperature due to molecular reconfiguration, that these changes outperform those observed in any type of caloric material, and that these changes are comparable with those exploited commercially in hydrofluorocarbons. Our discovery of colossal barocaloric effects in a plastic crystal should bring barocaloric materials to the forefront of research and development in order to achieve safe environmentally friendly cooling without compromising performance.Peer Reviewe