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Solid-state cooling based on i-caloric effects may be an alternative to conventional vapor-compression refrigeration systems. The adiabatic temperature change ($\Delta T_{S}$) is one of the parameters that characterize the i-caloric effects, therefore it is important to obtain the correct $\Delta T_{S}$ values and, whenever possible, to correlate this parameter with thermodynamic and microscopic quantities. In this work, we propose a comprehensive thermodynamic model that allows us to determine the adiabatic temperature change from non-adiabatic measurements of temperature change induced by a field change. Our model fits efficiently temperature versus time and temperature change versus the inverse of the field change rate data for three different materials presenting different i-caloric effects. The results indicate the present model is a very useful and robust tool to obtain the correct $\Delta T_{S}$ values and to correlate $\Delta T_{S}$ with other thermodynamic quantities., Comment: 13 pages, 3 figures, 1 table

The urge for efficient and environmentally friendly alternatives for the current gas-based refrigeration is becoming more critical due to global warming and overpopulation. Among the main candidates, solid-state-based cooling technology is appealing to substitute the conventional systems. Recently, attention has been turned to the barocaloric effect in advanced materials, namely, plastic crystals and elastomers, with reports revealing great caloric responses around room temperature for a series of materials. In this sense, this review has the goal of collecting, organizing and comparing the results from the literature to provide an outlook on the subject.

Specific heat and entropy are relevant thermodynamic properties, which may be used as macroscopic probes to microscopic properties of materials under ambient conditions and under high applied fields. However, the measurement of specific heat under intense external fields can be a challenging task, as well as to obtain the entropy in the same conditions. Here, we describe a method to obtain high-field specific heat and entropy from measurements of specific heat under ambient conditions and direct temperature change induced by adiabatic field changes. We derive straightforward thermodynamic equations to calculate the specific heat and entropy and our results agree satisfactorily with experimental data of specific heat under magnetic field, electric field, and pressure.

Elastomers have shown to be promising barocaloric materials, being suitable candidates for solid-state cooling devices. Moreover, this family of polymers presents additional advantages, such as their low cost and long fatigue life. In this context, we investigated the barocaloric effects in Nitrile Butadiene Rubber (NBR) in a large range around room temperature. Moderated applied pressures on NBR yield giant temperature change ({\Delta}TS) and entropy change ({\Delta}ST), reaching the maximum values of 16.4(2) K at 323 K and 59(6) J kg-1K-1 at 314 K, respectively, for a pressure change of 390 MPa. Besides, both {\Delta}TS and {\Delta}ST have shown to be rather reversible. An influence of the glass transition on the barocaloric effects was verified: the glassy state tends to diminish the entropy and temperature changes in comparison with the rubbery state. Furthermore, we calculated the pressure coefficient of glass transition (dTg/dP) obtained from different processes. Our study evidences the potential of NBR for cooling applications based on barocaloric effect, but also points out the glass transition must be avoided for a better barocaloric performance., Comment: 13 pages

The large magnetocaloric effect in Heusler alloys showing martensite phase transformation puts them forward as efficient materials for magnetic refrigeration. However, irreversibility of the magnetocaloric cooling cycle is a major challenge for real applications. This irreversibility is directly linked to the thermal hysteresis at the first-order martensite phase transition. Therefore, minimizing the hysteresis is essential in order to achieve reversibility. Here we show a large reduction in the thermal hysteresis at the martensite transition in the Ni$_{2}$Mn$_{1.4}$In$_{0.6}$ and Ni$_{1.8}$Co$_{0.2}$Mn$_{1.4}$In$_{0.6}$ Heusler alloys upon the application of hydrostatic pressure. Our pressure dependent X-ray diffraction study on Ni$_{2}$Mn$_{1.4}$In$_{0.6}$ reveals that with increasing pressure the lattice parameters of the two crystallographic phases (austenite and martensite) change in such a way that they increasingly satisfy the geometric compatibility (co-factor) condition. These results provide an opportunity to overcome the hysteresis problem and hence the irreversible behavior in Heusler materials using pressure as an external parameter., Comment: 11 pages main text plus 2 supplementary material

The Gd5.09Ge2.03Si1.88 compound, as well as other magnetocaloric materials, certainly will not be used in their un-manufactured as-cast condition in future magnetic refrigeration applications or other devices. In this work, we have studied the Gd5.09Ge2.03Si1.88 compound processed in different ways, mainly, the as-cast powder, the annealed powder and the pressed and sintered powder. The annealed powder (1370 K / 20 hours) does not present the monoclinic phase and the first-order-magneto-structural transition observed in the as-cast powder. The pressed and sintered powder also do not present the first-order transition. Furthermore, the compacting pressure shifts the second-order-magnetic transition to lower temperatures. The behavior of cell parameters as a function of the compacting pressure indicates that TC is directly affected by parameter c change., Comment: 12 pages, 4 figures, 1 table

Solid-state cooling based on caloric effects is considered a viable alternative to replace the conventional vapor-compression refrigeration systems. Regarding barocaloric materials, recent results show that elastomers are promising candidates for cooling applications around room-temperature. In the present paper, we report supergiant barocaloric effects observed in acetoxy silicone rubber - a very popular, low-cost and environmentally friendly elastomer. Huge values of adiabatic temperature change and reversible isothermal entropy change were obtained upon moderate applied pressures and relatively low strains. These huge barocaloric changes are associated both to the polymer chains rearrangements induced by confined compression and to the first-order structural transition. The results are comparable to the best barocaloric materials reported so far, opening encouraging prospects for the application of elastomers in near future solid-state cooling devices., Comment: 19 pages, 7 figures, 2 tables

Solid-state cooling based on i-caloric effects has shown to be a promising alternative to the conventional refrigeration devices. Only very recently, the research on barocaloric materials is receiving a deal of attention due to the demonstration of giant barocaloric effects in shape-memory alloys. Regarding polymers, there is still a lack of literature, despite their high caloric potential. Thus, we present here giant barocaloric effects in natural rubber, a low-cost and environmental friendly elastomer polymer. The maximum values of entropy and temperature changes are larger than those previously reported for any promising barocaloric material. Moreover, the huge normalized temperature change and refrigerant capacity exhibited by natural rubber confirm its high potential for cooling applications. We also verify a relevant dependence of the barocaloric effect on the glass transition in natural rubber. Our findings suggest that commercial refrigeration devices based on barocaloric effects from elastomer polymers can be envisaged in the near future., Comment: 22 pages, 8 figures, 2 tables. Corrected version. Corrected isothermal entropy change values and related results

This is a comment on 'Table-like magnetocaloric effect and enhanced refrigerant capacity in Eu8Ga16Ge30-EuO composite materials', published few years ago. Refrigerant Capacity (RC) and Relative Cooling Power (RCP) are properties that characterize the magnetocaloric effect. RCP and mainly RC are also important to characterize other i-caloric effects (electrocaloric and mechanocaloric effects). This comment intends to point out mistakes in a specific paper and to be helpful to prevent inappropriate comparisons between RC and RCP., Comment: 3 pages, 1 figure

The barocaloric effect is still an incipient scientific topic, but it has been attracting an increasing attention in the last years due to the promising perspectives for its application in alternative cooling devices. Here, we present giant values of barocaloric entropy change and temperature change induced by low pressures in PDMS elastomer around room temperature. Adiabatic temperature changes of 12.0 K and 28.5 K were directly measured for pressure changes of 173 MPa and 390 MPa, respectively, associated with large normalized temperature changes (~70 K GPa-1). From adiabatic temperature change data, we obtained entropy change values larger than 140 J kg-1 K-1. We found barocaloric effect values that exceed those previously reported for any promising barocaloric materials from direct measurements of temperature change around room temperature. Our results stimulate the study of the barocaloric effect in elastomeric polymers and broaden the pathway to use this effect in solid-state cooling technologies., Comment: 24 pages, 8 figures, 2 tables. Corrected version. Corrected isothermal entropy change values and related results

Barocaloric materials have shown to be promising alternatives to the conventional vapor-compression refrigeration technologies. Nevertheless, barocaloric effect ({\sigma}b-CE) has not been extensively examined for many classes of materials up to now. Aiming at fulfilling this gap, this paper describes the development of a high-pressure experimental setup for measuring the {\sigma}b-CE in polymers. The design allows simultaneous measurements of temperature, pressure and strain during the barocaloric cycle. The system proved to be fully-functional through basic experiments using natural rubber. Samples exhibited large temperature variations associated to the {\sigma}b-CE. Strain-temperature curves were also obtained, which could allow indirect measurements of the isothermal entropy change., Comment: 8 pages, 4 figures. Correction in Figure 4

Representative compounds of the new family of magnetic materials Gd5-xNdxSi4 were analyzed by X-ray diffraction at the XRD1 beamline at LNLS. To reduce X-ray absorption, thin layers of the powder samples were mounted outside the capillaries and measured in Debye-Scherrer geometry as usual. The X-ray diffraction analyses and the magnetometry results indicate that the behavior of the magnetic transition temperature as a function of Nd content may be directly related to the average of the four smallest interatomic distances between different rare earth sites of the majority phase of each compound. The quality and consistency of the results show that the XRD1 beamline is able to perform satisfactory X-ray diffraction experiments on high-absorption materials even off the best conditions., Comment: 12 pages, 3 figures, 3 tables