Large Adiabatic Temperature Change Research Articles

Colossal Reversible Barocaloric Effects in a Plastic Crystal Mediated by Lattice Vibrations and Ion Diffusion.

Solid-state methods for cooling and heating promise a sustainable alternative to current compression cycles of greenhouse gases and inefficient fuel-burning heaters. Barocaloric effects (BCE) driven by hydrostatic pressure (p) are especially encouraging in terms of large adiabatic temperature changes (|ΔT| ≈ 10K) and isothermal entropy changes (|ΔS| ≈ 100JK-1kg-1). However, BCE typically require large pressure shifts due to irreversibility issues, and sizeable |ΔT| and |ΔS| seldom are realized in a same material. Here, the existence of colossal and reversible BCE in LiCB11H12 is demonstrated near its order-disorder phase transition at ≈380K. Specifically, for Δp ≈ 0.23(0.10)GPa, |ΔSrev| = 280(200)JK-1kg-1 and |ΔTrev| = 32(10)K are measured, which individually rival with state-of-the-art BCE figures. Furthermore, pressure shifts of the order of 0.1GPa yield huge reversible barocaloric strengths of ≈2JK-1kg-1MPa-1. Molecular dynamics simulations are performed to quantify the role of lattice vibrations, molecular reorientations, and ion diffusion on the disclosed BCE. Interestingly, lattice vibrations are found to contribute the most to |ΔS| while the diffusion of lithium ions, despite adding up only slightly to the entropy change, is crucial in enabling the molecular order-disorder phase transition.

High energy-storage density and giant negative electrocaloric effect in PLZS antiferroelectric thick film ceramics prepared via the tape-casting process

Antiferroelectric materials are highly desired for high energy-storage density capacitors and electrocaloric refrigerator in the future due to their excellent energy storage properties and giant negative electrocaloric effect, which have attracted great attention in recent years. In the present work, a highly recoverable energy density (Wrec) and a large reversible adiabatic temperature change (ΔT) were obtained simultaneously in PLZS thick film ceramics (TFCs). A maximum Wrec of 9.84J·cm-3 with an efficiency of 85.2% at 440kV·cm-1, and a negative ΔT of -9.50 °C at 280kV·cm-1 were obtained. Moreover, the maximum value of electrocaloric strength of 0.98K·m·MV-1 was achieved for Pb0.97La0.02(Zr0.50Sn0.50)O3 TFCs. These results demonstrate that the PLZS TFCs can be applied potentially for high energy-storage density capacitors and refrigerators.

Large electrocaloric effect across the non-hysteretic electrostructural phase transition in lead-free (Ba0.88Ca0.12)(Ti0.94Sn0.06)O3 ceramics

Structural, dielectric, and electrocaloric properties were investigated in Pb-free ceramic (Ba0.88Ca0.12)(Ti0.94Sn0.06)O3 (BCST), synthesized using solid-state sintering method. Rietveld refinement of room temperature XRD data revealed the existence of pure perovskite tetragonal (P4mm) phase. Temperature-dependent XRD analyses confirmed a structural transition from tetragonal to cubic phase near 380 K. Temperature-dependent dielectric constant (εr) and specific heat capacity (Cp) confirmed the presence of thermal hysteresis in two phase transitions near 233±10K and 254±10K, and a non-hysteretic behavior at the Curie temperature (TC∼373±10K). A comprehensive Raman study corroborated the existence of phase transitions. Electrocaloric properties were determined using indirect method utilizing the non-hysteretic nature acrossTC. A large adiabatic temperature change of |∆T| = 0.52 K, isotropic entropy change |∆S| = 0.68 J/kg.K, electrocaloric coefficients, |∆T/∆E |= 0.311 K.mm/kV and |∆S/∆E| = 0.41 J.mm/K.kg.kV were obtained at 380 K for an electric field of 16.7 kV/cm. Obtained value of |∆T/∆E| is relatively good, reported among other BaTiO3-based ceramics.

Large electrocaloric effect and wide working area in the transition from ferroelectric to nanodomains

AbstractA large adiabatic temperature change along with a wide operating temperature region is usually required for the electrocaloric materials to fulfill their refrigeration function. In general, doping foreign ions into BaTiO3 is the frequently utilized strategy in order to obtain excellent electrocaloric materials for the practical application. In the current paper, BaTiO3 lead‐free ferroelectric ceramics were doped by Ca2+ and Sn4+ simultaneously in order to generate a coexistence state at room temperature, where ferroelectric domains and nanodomains exit. As a result, a large polarization and a wide operating temperature range were finally induced. It is found that Ba0.9Ca0.1Ti0.85Sn0.15O3 has a maximum adiabatic temperature change of 0.85 K and an excellent working temperature region (65 K, ∆T > 90% Tmax) was achieved under an electric field of 50 kV/cm. The above phenomenon indicates that the modified BaTiO3 ceramics can be a good potential electrocaloric material in the state of cross‐existence of ferroelectric domains and nanodomains.

Electrocaloric effect with enhanced temperature stability in an interfacial polarization controlled ferroelectric laminated composite

Research on zero-emission lead-free ferroelectric materials is fascinating in the field of solid-state refrigeration due to the observed large electrocaloric phenomenon. However, one of the challenges involved is realizing a large adiabatic temperature change ( ΔT ) over a wide temperature span. Here, a laminated ferroelectric structure with layers, having successive phase transitions covering room temperature, is proposed to overcome this problem. BaTi1−x Sn x O3 with x = 0.08, 0.12, and 0.15 compositions exhibiting the required ferroelectric Curie temperatures was chosen for the component layers. The designed interfacial polarization engineered laminated structure with 0.15/0.08/0.12 compositional layers yielded a value of adiabatic temperature change ΔT max ⩾ 0.6 °C by an indirect method using Maxwell’s thermodynamic equations over a wide temperature span (30 °C–85 °C). The observed results are correlated to the interrelated cumulative effect of reduced interfacial polarization, homogeneous electric field distribution, field-induced phase transitions, and enhanced domain switching, which are the manifestation of the designed laminated geometry.

Enhanced superelasticity and reversible elastocaloric effect in nano-grained NiTi alloys with low stress hysteresis

Solid-state cooling technologies have been considered as potential alternatives for vapor compression cooling systems. The search for refrigeration materials displaying a unique combination of pronounced caloric effect, low hysteresis, and high reversibility on phase transformation was very active in recent years. Here, we achieved increase in the elastocaloric reversibility and decrease in the friction dissipation of martensite transformations in the superelastic nano-grained NiTi alloys obtained by cold rolling and annealing treatment, with very low stress hysteresis (6.3 MPa) under a large applied strain (5%). Large adiabatic temperature changes (ΔT max = 16.3 K at ε = 5%) and moderate COPmater values (maximum COPmater = 11.8 at ε = 2%) were achieved. The present nano-grained NiTi alloys exhibited great potential for applications as a highly efficient elastocaloric material.

Room-temperature spin reorientation transition and low-temperature significant magnetothermal effect in Mn-doped DyFeO3 single crystals

Rare-earth orthoferrites (RFeO3) promise in spin storage and spin sensing, but the majority of the magnetic phase transition and intriguing properties occur at low temperatures. Searching for higher-temperature or even room-temperature spintronics devices has been a critical challenge in the development of spintronics. We doped Mn ions into Fe sites of DyFeO3 in 10%–50 % ratios to coexist antiferromagnetic and ferromagnetic coupling in the ab plane and elevate their spin reorientation transition (SRT) temperatures. The structural, magnetic, and magnetothermal properties of the Mn-doped DyFeO3 single-crystal system are investigated. With increasing doping ratio, the Néel temperature progressively falls, while the SRT temperature (TSR) continuously rises to the room temperature of 307 K with a 40 % doping ratio, making it promising for room-temperature spin storage devices. When the ratio reaches 50 % (half doping), the magnetic configuration of Dy sublattices changes and a significant magnetothermal effect is observed. Because of low-field metamagnetic phase transition, the magnetic entropy change along the c-axis approaches 10.41 J/kg·K for the half doping crystal at 5 K (0 J/kg·K for DyFeO3, 0.93 J/kg·K for orthorhombic DyMnO3). The large adiabatic temperature change contributed by magnon indicates the exceptional refrigeration efficiency in a direct way. Therefore, it is possible to convert DyFeO3 into a room-temperature spin storage device material or a magnetic refrigeration contender at low temperatures.

Strong electrocaloric response with ultrawide working temperature span in lead-free BaTiO3-based ceramics by composition design

Solid-state refrigeration technology based on electrocaloric effect provides a cost-effective and convenient approach for microelectronic device cooling. However, the working temperature range of electrocaloric materials is often narrow and incommensurate with that required by many microelectronic devices including computer chips and CPUs. In this work, the working temperature span of electrocaloric response in BaTiO3 ceramics were tuned by the simultaneous introduction of Sr and Hf (abbreviated as BSHT). Through rational variation of Sr and Hf content, not only the Curie temperature is reduced to ∼80 °C, but also the room-temperature phase structure of the ceramics can be effectively tuned from a single rhombohedral phase to coexistence of rhombohedral + orthorhombic or orthorhombic + tetragonal phases. Relaxor behavior of BSHT ceramics is evident by the frequency-dispersion of dielectric permittivity and the increased relaxor diffuseness factor γ. Temperature-dependent Raman spectra confirm that Ba0.85Sr0.15Hf0.06Ti0.94O3 (0.6BSHT) sustain a two-phase coexistence state over a broad temperature range. 0.6BSHT ceramics render a large adiabatic temperature change ΔT of 0.91 K under 40 kV cm−1 with a broad temperature span of ∼57 °C, covering the working temperature window of most microelectronic devices. Moreover, the electrocaloric response of 0.6BSHT shows excellent fatigue endurance, i.e., the adiabatic temperature change shows a trivial degradation of <4.4 % after 106 cycles. This work demonstrates that BaTiO3-based ceramics remain one of the most promising electrocaloric candidates and compositional modification is an effective route to tune the electrocaloric response for fulfilling the requirements of practical applications.

Imparting high elastocaloric cooling potential to NiTi alloy by two-step enhancements

The large adiabatic temperature change during the stress-induced phase transformation in the superelastic NiTi alloy makes it a leading candidate material for solid-state elastocaloric cooling applications. However, NiTi with a uniform grain structure generally offers either large cooling capacity or low energy dissipation, but not both. In an earlier study, we demonstrated that the alloy with graded grain sizes, obtained using differential annealing of heavily cold-worked sheets, can overcome this intrinsic limitation. However, non-transformable components (residual martensite and amorphous phases), which are introduced into the microstructure during cold rolling, impair the full exploitation of the cooling potential of the graded NiTi. Here, we introduce an intermediate processing step, namely post-deformation annealing, which eliminates the undesirable phases while maintaining nanocrystallinity, before imparting a microstructural gradient. Results show that the synergy between various microstructural elements results in a significant enhancement in the cooling capacity while keeping the energy dissipation low. Moreover, the functional fatigue performance of the graded alloy is also preferable to that of the conventional coarse-grained NiTi. The micromechanical reasons behind these improvements are elucidated by recourse to detailed experiments.

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.

Excellent elastocaloric and mechanical performance in Mn-doped Co–V-Ga as-cast polycrystalline alloy with simple preparation

With the rapid development of solid-state refrigeration technology, elastocaloric materials face higher requirements, such as a higher elastocaloric effect (eCE), better mechanical properties, and simpler and faster large-scale preparation. In this work, we propose a composition design strategy for Mn-doped Co–V-Ga shape memory alloys, which can enhance both the eCE and the mechanical properties. We combine first-principles calculations and experiments to demonstrate this strategy. Our results reveal that the lattice distortion caused by the difference in atomic radii produces a solid-solution-strengthening effect within the alloy, impeding dislocation motion and significantly improving the mechanical properties. Through composition optimization, the low-cost Co51.7V31.3Ga14.75Mn2.25 as-cast polycrystalline alloy exhibits a large adiabatic temperature change (ΔTad) of −11.2 K at room temperature, while its maximum compressive strength and strain can reach up to 1859 MPa and 26% at room temperature, respectively. Importantly, the alloy exhibits excellent cycle stability, and its ΔTad does not decay after 100 loading and unloading cycles, indicating that it has the potential for practical application. Further comparison with the annealed sample shows that the secondary defects deteriorate the ΔTad of the alloy. Our research provides an effective strategy for the simple, rapid and large-scale production of as-cast eCE alloys.

Enhanced electrocaloric effect over a broad temperature range in lead‐free Na0.5Bi0.5TiO3‐based relaxor ferroelectrics via doping with Bi(Mg0.5Zr0.5)O3

AbstractWith an increasing demand for environmentally friendly refrigeration, the solid‐state refrigeration based on the electrocaloric effect (ECE) has been drawn extensive attention. It is a challenge to maintain a large adiabatic temperature change (∆T) over a broad temperature span. Herein, the authors designed and synthesised (0.74‐x) Na0.5Bi0.5TiO3‐0.06BaTiO3‐0.2SrTiO3‐xBi(Mg0.5Zr0.5)O3 (abbreviated as NBT‐xBMZ) (x = 0, 0.02, 0.04, 0.06 and 0.08) lead‐free relaxor ferroelectrics. Their microstructures, dielectric properties, ferroelectric properties, ECEs and the structure‐property relationships were investigated. Via doping with BMZ, an enhanced relaxor feature and a wider temperature range where multi‐phases coexist were achieved. The relaxor ferroelectric characteristics were illustrated using the Vogel‐Fulcher relation. The indirectly calculated ECE results showed that the optimal ΔT of 1.11 K was obtained for the x = 0.02 sample at 90°C and 70 kV/cm over a wide Tspan of 120°C, providing a potential ECE material. The direct ECE results procured using thermocouple indicated that the maximal ∆T of 2.14 K and ∆T/∆E of 0.31 K m/MV were achieved in the same sample at 70°C and 7 MV/m and the variation trend of ECE results was consistent with the indirect results. Moreover, the multi‐phases coexistent strategy can be extended to other materials system to generate a large ΔT over a wide temperature range.

Optimized Electrocaloric Refrigeration in Lead-Free NaNbO3-Based Ceramics via AFE ↔ FE Phase Transition Modulation.

An outstanding challenge for eco-friendly ferroelectric (FE) refrigeration is to achieve a large adiabatic temperature change within a broad temperature range originating from the electrocaloric (EC) effect, which is expected to be realized in antiferroelectric (AFE) materials owing to the large entropy change during electric field and thermally induced phase transition. In this work, a large EC response over a wide response temperature range can be achieved slightly above room temperature via designing the phase transition of NaNbO3. An irreversible to reversible AFE-FE phase transition on heating induced by the introduction of CaZrO3 into NaNbO3 plays a key role in the optimized electrocaloric refrigeration. Accordingly, accompanying the local structure transformation corresponding to the B-site ions, the transition temperature between the square polarization-electric field (P-E) hysteresis loop (the irreversible AFE-FE phase transition induced by the electric field) and the repeatable double P-E hysteresis loop (the electric field induced reversible AFE-FE phase transition) was tailored to around room temperature, in favor of extending large entropy change to the wide temperature range. This work provides an efficient approach to designing lead-free EC materials with excellent EC performance, promoting the advancement of environmentally friendly solid-state cooling technology.

Miniature-scale elastocaloric cooling by rubber-based foils

We report on the design and characterization of a demonstrator device for miniature-scale elastocaloric (eC) cooling using a series of natural rubber (NR) foil specimens of 9 × 26.5 mm2 lateral size and thicknesses in the range of 290–900 μm. NR has the potential to meet the various challenges associated with eC cooling, as it exhibits a large adiabatic temperature change in the order of 20 K and high fatigue resistance under dynamic load, while loading forces are low. Owing to the large surface-to-volume ratio of rubber-based foils, heat transfer to heat sink and source elements is accomplished by mechanical contact enabling compact designs. Two actuators are implemented to control the performance in loading direction independent from the performance of mechanical contacting. The study of operation parameters is complemented by lumped-element modeling to understand the cycle frequency-dependent dynamics of heat transfer and resulting cooling capacity. The single-stage device operates in the strain range of 300%–700% and exhibits a temperature span up to 4.1 K, while the specific cooling power reaches 1.1 Wg−1 and the absolute cooling power 123 mW. The performance metrics show a pronounced dependence on foil thickness and heat transfer coefficient indicating a path toward future device optimization.

Electrocaloric behaviour of tape cast and grain oriented NBT-KBT ceramics

We have investigated the effects of grain orientation and tape casting process on the electrocaloric properties of 0.82Na0.5Bi0.5TiO3-0.18 K0.5Bi0.5TiO3 (0.82NBT-0.18KBT) ceramics at the Morphotropic Phase Boundary (MPB), using direct and indirect measurements. We observe a larger electrocaloric response for the template-free ceramics compared to 7 and 10 wt% template containing ones, suggesting that grain orientation along rhombohedral < 100 > does not improve the electrocaloric response. Indirect measurements yielded a large adiabatic temperature change of around 3 K under an electric field of 50 kV/cm, which is significantly higher than 0.9 K reached at a lower electric field of 40 kV/cm using the direct measurement.

Significant enhancement of magnetocaloric effects via tuning Curie temperature and magnetic anisotropy in rare-earth based compounds

Magnetic refrigeration (MR) research has been increasingly focused on targeting operation temperatures as low as 4.4–20 K, which is of strategic significance for liquid helium and hydrogen in various activities such as aerospace and highly advanced industries. To date, despite most research has been aimed at obtaining MR materials with large magnetic entropy change and adiabatic temperature change, the optimizing operation temperature to target the cooling range for helium-hydrogen liquefaction is highly desirable and valuable. Here, the significant enhancement in magnetocaloric effects (MCEs) and magnetic materials operating in the temperature range of 4.4–20 K are achieved. The magnetic properties and MCEs of HoCuAl are manipulated by substituting Er or Tm atoms with the lower de Gennes factor and various magnetic anisotropy. The maximum magnetic entropy change ((−ΔSM)max) and refrigeration capacity (RC) under 0–5 T for Ho0.9Er0.1CuAl increases by 25.8 % and 39.8 % respectively compared with HoCuAl compound. Additionally, the critical role of Curie temperature and magnetic anisotropy in the significant enhancement of MCEs is confirmed by the systematic macroscopic physical analysis and neutron diffraction measurements. The excellent MCEs, suitable operation temperature, and free of hysteresis loss demonstrate the promising application prospect in liquefaction of helium-hydrogen.

Enhanced electrocaloric effect in KNN-based ceramic via polymorphic phase transition

A large adiabatic temperature change (ΔT) in lead-free ceramics is highly desired to develop eco-friendly and high efficiency solid-state refrigeration device based on electrocaloric effect (ECE). However, a large ΔT is often obtained near high Curie temperature (Tc > 100 °C), which impedes the practical applications for electrocaloric refrigeration technology. Herein, the lead-free (1-x)(K0.48Na0.535)0.03Li0.07(Nb0.99Sb0.01)O3-xBaZrO3 (x = 0, 0.02, 0.04 and 0.06) ceramics were synthesized through a conventional solid-state sintering method. A polymorphic phase transition (PPT) region is constructed by composition engineering to achieve large ECE near the ambient temperature. A ΔT of 0.48 K under 50 kV/cm is obtained at 60 °C by using the direct measurement in KNLNS-0.02BZ ceramic with coexistence of R-O-T phase. This work suggests that building multi-phase coexistence is a feasible design scheme in order to achieve ECE near the room temperature.

Fatigue-resistant elastocaloric effect in hypoeutectic TiNi58 alloy with heterogeneous microstructure

Shape memory alloys with high fatigue life and large adiabatic temperature change (ΔTad) are critical for elastocaloric effect in practical solid-state refrigeration applications. Here, we report on the discovery of a hypoeutectic TiNi58 alloy by heterogeneous microstructure design to perform ΔTad of 6.1 K after 2 million fatigue loading-unloading cycles. The fatigue-resistant elastocaloric effect is achieved by a highly reversible quasi-linear superelasticity with strength of 2.2 GPa and modulus of 44.9 GPa. Such stable mechanical behavior is attributed to the prepared unique heterogeneous microstructure, as characterized by multi-scale microscopic analysis. The heterogeneous microstructure is consisted of dendrite regions with Ti2Ni3 precipitates and the surrounding eutectic structure with lath TiNi3 phase. The lath intermetallic TiNi3 phase surrounding dendrite regions works as skeletal reinforcement, providing extra mechanical fatigue stability and giving rise to high strength. The cubic structured Ti2Ni3 precipitates produce local lattice strain due to lattice mismatch within the surrounding B2 matrix with near equiatomic composition. Detailed phase-field simulation based on the local strain field distribution in B2 matrix reveals a continuous transition behavior of martensite under external loads distinct from conventional stress-induced violent autocatalytic martensitic transformation, which is the origin of controlled strain release in quasi-linear superelasticity with ultrahigh fatigue stability. This work demonstrates the potential of hypoeutectic TiNi58 alloy for long-term elastocaloric service and provides guidance to design new elastocaloric materials with high fatigue resistance in bulk mass through simple controlled casting process.

Orientation dependence of elastocaloric effect in a Cu71.3Al17.5Mn11.2 single crystal

In this work, the orientation dependence of superelasticity and elastocaloric effect was systematically investigated in a Cu71.3Al17.5Mn11.2 single crystal, which was prepared by means of abnormal grain growth induced by cyclic heat treatment using a < 001 >A textured polycrystalline alloy as the precursor. By comparing the superelastic and elastocaloric response upon applying the compressive loading along the < 001 >A, < 110 >A and < 111 >A orientations, it was shown that the < 001 >A orientation can yield the largest transformation strain, the lowest transformation stress and the most remarkable elastocaloric response. Large stress-induced adiabatic temperature change (|ΔTad|) values of 12 K ∼ 15 K, covering a wide temperature window from 293 K to 453 K, were achieved upon removing a compressive loading of 500 MPa for the < 001 >A oriented single crystal. Moreover, favored by the relatively lower driving stress along the < 001 >A orientation, the specific adiabatic temperature variation (|ΔTad/σmax|) can be as large as 107.3 K/GPa. This work clearly demonstrates the strong influence of crystallographic orientation on the elastocaloric properties resulting from stress-induced martensitic transformation, which is expected to provide some instructions for designing high-performance elastocaloric materials.

Ni-Co-Mn-Ti-B high performance multiferroic phase transformation material: Simultaneous modulation of mechanical properties and successive caloric effects by B doping

Ni-Mn-based multiferroic phase transformation materials are emerging as one of the most promising candidates in the field of solid-state refrigeration. However, the high intrinsic brittleness and the narrow working temperature region of these alloys limit their practical applications. Here, we demonstrate a composition design strategy for B doping in Ni-Co-Mn-Ti alloys, which simultaneously improves mechanical properties and maintains giant successive caloric effects with a broad working region near room temperature (RT). Our results reveal that the original Ti-rich second phase in the Ni-Co-Mn-Ti alloys has little contribution to the mechanical properties, while the grain refinement and grain boundary strengthening mechanisms formed by the doping of B can ensure the excellent mechanical properties. Through composition optimisation, the low-cost (Ni37Co13Mn34Ti16)98.5B1.5 as-cast alloy prepared by arc-melting can exhibit excellent mechanical properties and functional behaviour. The fracture compressive strength and strain of alloy can reach up to 1553 MPa and 17.7% at 290 K, respectively. Besides, the maximum magnetic entropy change induced by 70000 Oe magnetic field is 40.3 J kg−1 K−1, and a large elastocaloric adiabatic temperature change of 18.0 K can be yielded through applying a stress field. A combination of magnetocaloric and elastocaloric effect can achieve a broad working temperature region of over 90 K.