Giant Adiabatic Temperature Change Research Articles

Giant adiabatic temperature change and its direct measurement of a barocaloric effect in a charge-transfer solid

Solid refrigerants exhibiting a caloric effect upon applying external stimuli are receiving attention as one of the next-generation refrigeration technologies. Herein, we report a new inorganic refrigerant, rubidium cyano-bridged manganese–iron–cobalt ternary metal assembly (cyano-RbMnFeCo). Cyano-RbMnFeCo shows a reversible barocaloric effect with large reversible adiabatic temperature changes of 74 K (from 57 °C to −17 °C) at 340 MPa, and 85 K (from 88 °C to 3 °C) at 560 MPa. Such large reversible adiabatic temperature changes have yet to be reported among caloric effects in solid–solid phase transition refrigerants. The reversible refrigerant capacity is 26000 J kg−1 and the temperature window is 142 K. Additionally, cyano-RbMnFeCo shows barocaloric effects even at low pressures, e.g., reversible adiabatic temperature change is 21 K at 90 MPa. Furthermore, direct measurement of the temperature change using a thermocouple shows +44 K by applying pressure. The temperature increase and decrease upon pressure application and release are repeated over 100 cycles without any degradation of the performance. This material series also possesses a high thermal conductivity value of 20.4 W m−1 K−1. The present barocaloric material may realize a high-efficiency solid refrigerant.

Giant electrocaloric effect and high-field electrostrictive properties in Ba(Ti1−xSnx)O3 ceramics

One of the emerging solid-state refrigeration technologies to replace classic compression refrigeration is electrocaloric refrigeration, which has the advantages of high energy conversion efficiency, easy miniaturization, eco-friendliness, and low cost. In this paper, Ba(Ti1−xSnx)O3 (BTSn) ceramics with x = 0.02–0.08 were prepared by a solid-state reaction route. The structural, dielectric, ferroelectric, electrocaloric as well as electrostrictive characteristics were thoroughly examined. Our results show that the dielectric peaks correlated to the maximal permittivity move towards to low temperature direction when the Sn4+ concentration gradually increases, and a phase diagram of BTSn based on the dielectric characteristics is given. More importantly, in the x = 0.04 ceramic sample synthesized by the viscous polymer process, a giant adiabatic temperature change (ΔT) of 6.36 K with a temperature range of 25 °C at 200 kV/cm is achieved. Typically flare shape electrostrain curves accompanying with small hysteresis are observed in all studied compositions. The average electrostrictive coefficient Q33 varies within 0.0257–0.0306 m4/C2 at a temperature region from 30 to 160 °C, indicating temperature-insensitive and composition-insensitive characteristics. This research shows that a significant electrocaloric effect can be achieved in BTSn ceramics through high electric field, and would provide a strategy for boosting the electrocaloric effect in other systems.

Ultrahigh cyclic stability and giant elastocaloric effect in directionally solidified (Ni50Mn28Fe2.5Ti19.5)99.4B0.6 alloy

Cyclic stability of elastocaloric materials is critically important for practical applications in solid-state refrigeration. Ni-Mn-based Heusler-type alloys exhibit a large elastocaloric response to low driving stress. However, these alloys can only be worked for short-term cyclic operation due to their intrinsic brittleness. Here, we demonstrate the achievement of giant elastocaloric effect (eCE) and long-term fatigue performance in a directional solidification (Ni50Mn28Fe2.5Ti19.5)99.4B0.6 alloy. At 303 K, the maximum compressive strength and strain of the alloy can be as high as 2734 MPa and 20.5%, respectively. During fast loading and unloading with the stress of 435 MPa and the strain of 8%, giant adiabatic temperature change (ΔTad) of 25.1 K and -24.5 K can be obtained, respectively. In particular, a large ΔTad of about 5.8 K is generated during cycling at 360 MPa stress and 3.5% strain, and can be maintained for more than 20,000 cycles.

Enhanced elastocaloric effect and specific adiabatic temperature variation in Ni-Mn-In-Si-Cu shape memory alloys

In this work, we demonstrate a giant elastocaloric effect in a Ni50Mn33In14Si1Cu2 alloy. Owing to the large transformation entropy change and low thermal hysteresis, giant adiabatic temperature change (ΔTad) of − 18.2 K is obtained on unloading from a maximum compressive strain of 6 % with a low stress of 145 MPa. Moreover, large specific adiabatic temperature variation (ΔTad/σmax) up to 126 K/GPa has been achieved. This ΔTad/σmax value significantly exceeds those in the typical shape memory alloys. The present results demonstrate that the target alloy exhibits a distinct advantage in the strength of elastocaloric effect, being crucial for practical applications of solid-state refrigeration. In addition, it is found that the cyclic stability can be effectively enhanced by one-step overstress superelastic training for the first cycle.

Achieving enhanced mechanical, pseudoelastic and elastocaloric properties in Ni-Mn-Ga alloys via Dy micro-alloying and isothermal mechanical cyclic training

In the present study, the combination of Dy micro-alloying and isothermal mechanical cyclic training (IMCT) was utilized to enhance the mechanical, pseudoelastic and elastocaloric properties of Ni-Mn-Ga shape memory alloys. The formation of granular DyNi4Ga precipitates contributed to remarkable improvement in both strength and ductility. The IMCT treatment produced a strong <001>NM preferred orientation through variant-selection and created internal stress, and thus resulted in significant increment in transformation strains and adiabatic temperature changes. Specifically, a giant adiabatic temperature change of -12.5 °C was achieved in the trained alloys, which was the highest value reported so far in Ni-Mn-Ga based shape memory alloys.

Martensitic transformation and elastocaloric effect of Co51.5+xV31.5-xGa17 (x = 0.1, 0.2, 0.3) alloys

Co-V-Ga alloy, a newly discovered multifunctional material based on martensitic transformation (MT), has promising application prospects in spintronics and solid-state refrigeration fields. In this work, we investigated the MT behaviors and the elastocaloric effect (eCE) of Co51.5+xV31.5-xGa17 (x = 0.1, 0.2, 0.3) alloys. The alloys undergo a MT from paramagnetic austenite to paramagnetic martensite, accompanying by a large latent heat (about 6–9 J g−1). The MT temperature increases with the increase of the ratio of Co to V. The digital image correlation (DIC) combined with infrared thermography (IR) techniques were utilized to in situ characterize the stress-induced MT and temperature change of the sample. For the sample of x = 0.2, at a testing temperature of 301 K, it heats with a giant adiabatic temperature change up to 13.4 K upon loading, while cools only 2.4 K when stress releasing, showing an irreversible eCE. Raising the test temperature (319, 327 and 333 K) can greatly improve the reversibility of the eCE. Such an asymmetric elastocaloric temperature change at 301 K is closely related to the irreversibility of stress-induced MT, which can be attributed to several factors including the self-cooling effect, heat dissipative mechanism and the valence bond structure of Co-V-Ga alloys.

Achieving excellent superelasticity and extraordinary elastocaloric effect in a directionally solidified Co-V-Ga alloy

We demonstrate excellent superelasticity and giant elastocaloric effect in a directionally solidified Co50.7V33.3Ga16 alloy. Owing to the formation of [001]A preferentially oriented columnar grains, the as-grown alloy displays nearly perfect superelastic behaviors with fully reversible compressive strain of up to 5.4%, narrow stress hysteresis of about 40 MPa and a wide operating temperature window from 258 to 373 K. Simultaneously, a giant adiabatic temperature change ΔTad of -18.7 K is obtained on removing a uniaxial stress of 400 MPa at room temperature, which is in good agreement with the theoretical values based on Maxwell relation (-19.0 K) and calorimetric measurements (-19.9 K). A large |ΔTad| of greater than 12.5 K is obtained over a wide temperature span of at least 115 K. Moreover, both superelasticity and elastocaloric effect remain good functional stability without any evident degradation for 100 cycles.

Giant low-field actuated caloric effects in a textured Ni43Mn47Sn10 alloy

In this work, based on composition adjusting and texture control, we demonstrate giant elastocaloric and magnetocaloric effects in a directionally solidified Ni43Mn47Sn10 polycrystalline with strong <001>A texture. On removing a low compressive stress of 210 MPa, giant adiabatic temperature change up to −17.3 K is achieved. Such value is much higher than those in some elastocaloric materials reported previously. Besides, giant magnetic field induced entropy changes of 23.5 Jkg−1K−1 and 37.1 Jkg−1K−1 are also obtained under the magnetic field changes of 2 T and 5 T, respectively. Simultaneously achieving giant elastocaloric and magnetocaloric effects actuated by relatively low external field is of great importance to explore multi-caloric or coupled caloric effects in developing efficient and eco-friendly solid-state refrigeration technology.

Giant elastocaloric effect and exceptional mechanical properties in an all-d-metal Ni–Mn–Ti alloy: Experimental and ab-initio studies

Exploring novel materials with superior elastocaloric effect (eCE) is a central issue for the development of eCE refrigeration technique. In this work, we report a giant adiabatic temperature change ΔTad of −20.4 K in the 〈100〉-textured all-d-metal Ni50Mn31.75Ti18.25 bulk alloy. The ΔTad value, comparable to that of the sate-of-the-art Ni–Ti alloys, surpasses the existing conventional Ni–Mn-based alloys. Investigations show that the giant ΔTad is attributed to the large lattice volume change during martensitic transformation and the negligible negative contribution of magnetic entropy change owing to its weak magnetism. By performing X-ray diffraction measurements and ab-initio calculations, the weak magnetism is found to be intrinsically related to the B2 ordered structure in which the magnetic moments of the antiferromagnetically coupled Mn atoms located at 4a and 4b sites are cancelled out each other. Both experimental and theoretical studies confirm that Ni–Mn–Ti alloys possess the significantly enhanced mechanical properties compared with the conventional Ni–Mn-based alloys. Electronic structure investigations reveal that this could be ascribed to the replacement of d-d interaction for the strongly covalent p-d hybridization. Outstanding elastocaloric effect of the all-d-metal alloy opens a door for searching novel promising materials used as the elastocaloric refrigerants.

Influence of austenite ferromagnetism on the elastocaloric effect in a Ni44.9Co4.9Mn36.9In13.3 metamagnetic shape memory alloy

We demonstrate the temperature dependent elastocaloric effect in a Ni44.9Co4.9Mn36.9In13.3 polycrystalline alloy with a strong ⟨001⟩A preferred orientation. It is found that the adiabatic temperature changes induced by the compressive stress increase with the increase in testing temperature. The giant adiabatic temperature change up to 14.7 K is achieved on loading at 390 K, which is much higher than that around room temperature. Such a temperature enhanced effect is attributed to the reduced magnetic contribution to the transformation entropy through narrowing the temperature interval between magnetic transition and martensitic transformation controlled by the mechanical stress.

Lead-Free Bilayer Thick Films with Giant Electrocaloric Effect near Room Temperature.

Electrocaloric refrigeration utilizing ferroelectrics has recently gained tremendous attention because of the urgent demand for solid-state cooling devices. However, the low room-temperature electrocaloric effect and narrow operation temperature window hinder the implementation of lead-free ferroelectrics in high-efficiency cooling applications. In this work, chemical engineering and thick-film architecture design strategies were integrated into a BaTiO3-based system to resolve this challenge. Novel environmental-friendly Ba(Zr0.20Ti0.80)O3-Ba(Sn0.11Ti0.89)O3 (BZT-BST) bilayer films of ∼13 μm in single-layer thickness were prepared by the tape casting process. A giant adiabatic temperature change, Δ T ∼ 5.2 K, and a large isothermal entropy change, Δ S ∼ 6.9 J kg-1 K-1, were simultaneously achieved at room temperature based on the direct measurements, which are much higher than those reported previously in many lead-free ferroelectrics. Moreover, the BZT-BST thick films exhibited a remarkably widened operation temperature range from about 10 to 60 °C. These outstanding properties were mainly attributed to the multiphase coexistence near room temperature, relaxor ferroelectric characteristics, and improved electric-field endurance of the bilayer thick films. This work provides a guideline for the development of environment-friendly electronic materials with both ultrahigh and stable electrocaloric performance and will broaden the application areas of lead-free ferroelectrics.

Large elastocaloric effect driven by stress-induced two-step structural transformation in a directionally solidified Ni55Mn18Ga27 alloy

The first-order inter-martensitic transformation induced by temperature change or external stress is frequently observed in Ni-Mn-Ga alloys. Here, the inter-martensitic transformation is exploited to strengthen the elastocaloric effect. Through the stress-induced two-step structural transformation, i.e., martensitic and inter-martensitic transformation, giant adiabatic temperature change up to −10.7K is obtained in a directionally solidified Ni55Mn18Ga27 polycrystalline alloy with 〈001〉A preferred orientation, representing the highest value so far in Ni-Mn-Ga alloys. It is demonstrated that microstructure texturing together with introduction of inter-martensitic transformation could be an effective route to improve the elastocaloric properties in polycrystalline NiMn-based alloys.

Giant electrocaloric effect in ferroelectric ultrathin films at room temperature mediated by flexoelectric effect and work function

In ferroelectric ultrathin films, built-in electric fields are often present due to the flexoelectric effect and the difference of work functions at asymmetric electrodes, which may change the properties of the materials. In this paper, the influence of build-in electric fields induced by flexoelectric effect and/or work function difference on the misfit strain-temperature phase diagrams, and the electrocaloric properties of epitaxial BaTiO3 ultrathin films are investigated by using an extended nonlinear thermodynamic theory. It is found that the flexoelectric effect, i.e., the coupling of polarization and strain gradient, changes the misfit strain-temperature phase diagrams notably, in which the phases with out-of-plane polarizations increase due to the presence of a built-in field. The electrocaloric properties are remarkably enhanced when the built-in fields induced by both the flexoelectric effect and work function difference are considered. In particular, a giant adiabatic temperature change of 7.89 K in ultrathin Pt/BaTiO3/SrRuO3 capacitors at 460 K is predicted. Moreover, it is demonstrated that the peak of adiabatic temperature change versus working temperature is shifted from a high temperature to room temperature, suggesting that ferroelectric ultrathin films with asymmetric electrodes and strain gradient are promising candidates for room temperature refrigeration.

Giant elastocaloric effect and its irreversibility in [001]-oriented Ni45Mn36.5In13.5Co5 meta-magnetic shape memory alloys

In this letter, we investigate the elastocaloric reversibility in Ni-Mn-In-Co meta-magnetic shape memory alloys. A highly [001] textured Ni45Mn36.5In13.5Co5 polycrystalline alloy was grown by using the liquid-metal-cooling directional solidification technique. We have observed a giant adiabatic temperature change (ΔT) of +8.6 K caused by the stress-driven complete martensitic transformation. The asymmetry of the maximum ΔT between loading and unloading strongly depends on the magnitude of superelastic strain. Such an irreversible behavior is ascribed to the friction energy dissipation as well as the variation of the elastocaloric entropy change by shifting initial temperatures.

Modeling of a Smart Heat Pump Made of Laminated Thermoelectric and Electrocaloric Materials

In this study, a smart heat pump, which could be used for the cooling of electronics, made of laminated structure of thermoelectric (TE) and electrocaloric (EC) materials, is studied. A simple arrangement of two TE layers sandwiched with one EC layer is modeled. This smart heat pump utilized the newly developed EC materials of giant adiabatic temperature change and the TE materials of high figure of merit. The system has the advantages of no moving parts, made of solid state, operable over large working temperature difference, and can be formed into very small size. The operation of the device is numerically modeled considering the three major parametric effects: EC operation as a function of time, electric current applied on TE, and temperature difference between the hot and cold sinks. The results on coefficient of performance (COP) and heat flow per unit area are discussed. This study is performed as an early attempt of analyzing the basic physical features of TE–EC–TE laminated structure heat pump and extends the understanding by further discussing the tradeoff between lower COP and larger overall temperature difference coverage in the TE/EC hybrid heat pump system with multilaminated structure.

Giant adiabatic temperature change in FeRh alloys evidenced by direct measurements under cyclic conditions

We report on (1) direct measurements of ΔTad for binary Fe49Rh51 during field cycling and (2) maximum possible ΔTad measured under discontinuous protocol. Our results show that the ΔTad is 9.2 K on the first application of magnetic field of Δμ0H = 1.9 T and it remains as high as 6.2 K during the cycling in alternated field of the same magnitude. In addition, the adiabatic temperature change and magnetic entropy change under the first application of magnetic field and under cyclic conditions were determined indirectly using three different approaches: (1) from magnetic measurements (M(T)H dependences, Maxwell relations), (2) from calorimetry (C(T)p,H, S-T diagram) and (3) from H-T diagram. While the indirectly measured maximum possible ΔTad lies in the range of 10.5–12 K, the reduced value of ΔTad measured directly under cycling (6.2 K) is still extraordinarily high and is 15% higher than in Gd in similar magnetic field. This demonstrates the potential of materials with a first order metamagnetic transition for magnetocaloric applications despite the presence of hysteresis.

Giant electrocaloric effect in ferroelectric nanotubes near room temperature.

Ferroelectric perovskite oxides possess large electrocaloric effect, but only at high temperature, which limits their potential as next generation solid state cooling devices. Here, we demonstrate from phase field simulations that a giant adiabatic temperature change exhibits near room temperature in the strained ferroelectric PbTiO3 nanotubes, which is several times in magnitude larger than that of PbTiO3 thin films. Such giant adiabatic temperature change is attributed to the extrinsic contribution of unusual domain transition, which involves a dedicated interplay among the electric field, strain, temperature and polarization. Careful selection of external strain allows one to harness the extrinsic contribution to obtain large adiabatic temperature change in ferroelectric nanotubes near room temperature. Our finding provides a novel insight into the electrocaloric response of ferroelectric nanostructures and leads to a new strategy to tailor and improve the electrocaloric properties of ferroelectric materials through domain engineering.

Effect of surface tension on electrocaloric effects in the ferroelectric nanomaterial with vortex domain structures

The influence of intrinsic surface tension on the electrocaloric effect (ECE) in the ferroelectric nanomaterial with vortex domain structures is studied by using the phase field method. The calculation results show that a giant adiabatic temperature change (ΔT = 5.8 K) related to the toroidal moment change appears in the PbTiO3 (PTO) ferroelectric nanoparticle with the surface tension coefficient μ = 5 N/m under the vorticity vector of curled electric field (Q1 = 0 mV/Å2, ΔQ1 = 0.9 mV/Å2) at room temperature. The magnitude of the adiabatic temperature change decreases with the increase in surface tension. The decrease in size is found to enhance the ECE of PTO nanoparticle with vortex domain structures when the surface tension is not considered.