We present an investigation on structure, magnetic and magnetocaloric properties of the perovskite manganites (La1−xSmx)0.67Pb0.33MnO3 (x = 0, 0.1, 0.2, 0.3) synthesized by sol–gel technique. The XRD ...patterns show that all synthesized samples have reflections typical of the perovskite structure with orthorhombic symmetry. Thermomagnetic measurements showed that all the samples display a paramagnetic–ferromagnetic transition with decreasing temperature. The Curie temperature decreases with increasing Sm content from 358 K for x = 0–286 K for x = 0.3. We determined the isothermal magnetic entropy changes of all the samples from the magnetization measurements and furthermore measured the adiabatic temperature change of the sample for x = 0.3 directly. The results showed that the adiabatic temperature change, determined using together the entropy change and the specific heat and the value obtained by direct temperature change measurements both give 1.3 K for a magnetic field change of 3 T at about 280 K. We also measured the cyclic adiabatic temperature-change of the sample and the results indicate that the sample undergoes a reversible temperature-change on field-cycling which is essential for magnetic refrigeration.
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•Magnetocaloric properties of (La1−xSmx)0.67Pb0.33MnO3 (0.0 ≤ x ≤ 0.3) have been studied.•The TC decreases with increasing Sm-content from 358 K for x = 0.0–286 K for x = 0.3.•-ΔSMmax values change from 3.32 J/kgK for x = 0.0–2.60 J/kgK for x = 0.3 at 2 T.•We have measured directly the adiabatic temperature change to be 1.31 K in 3 T.•We have measured the zero-field heat capacity and estimated the ΔTadest to be 1.28 K.
Achieving appreciable elastocaloric effect under low external field is critical for solid-state cooling technology. Here, a non-isothermal Phase-Field Model (PFM) coupling martensitic transformation ...with mechanics, heat transfer and magnetostrictive behavior is proposed to simulate Magneto-elastoCaloric Effect (M-eCE) that is induced by magnetic field in a multiferroic composite (e.g., Magnetostrictive-Shape Memory Alloys (MEA-SMA) composite). In the PFM, a nonlinear constitutive hyperbolic tangent model is utilized to model the macroscopic magnetostrictive behavior of MEA, and the heat transfer coupled with phase transformation is employed to calculate the adiabatic temperature change (ΔTad) during M-eC cooling cycles. The influences of magnetic field, geometrical dimension, and ambient temperature on ΔTad are comprehensively investigated. Machine Learning (ML) is further conducted on the database from PFM simulations to accelerate the prediction and design of MEA-SMA composite with an improved ΔTad. It is found that a large ΔTad of 10–14 K and a wide working temperature window of 30 K can be achieved under ultra-low magnetic field of 0.15–0.38 T by optimizing the composite’s geometrical dimension. The present work combining PFM and ML for evaluating M-eCE provides a theoretical framework for the optimization of M-eC cooling devices, and is also potentially extended to other multicaloric effects (e.g., electro-elastocaloric effect).
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•A non-isothermal phase-field model is proposed for magneto-elastocaloric effect (M-eCE).•Effects of magnetic field, geometric dimension, and ambient temperature on M-eCE are revealed.•A large temperature change of 10–14 K is achieved by a low magnetic field (0.15–0.38 T).•Machine learning is used to accelerate the prediction and optimization of M-eCE.
•Electrocaloric effects in (SrBa)(SnTi)O3 ceramics were investigated using direct and indirect approaches.•The largest electrocaloric strength obtained is 0.52 × 10−6 K m/V at T = 56 °C and E = 2 ...MV/m.•An analytic formula of electrocaloric strength (dT/dE) was firstly deduced via a thermodynamic theory.•The electrocaloric strength mainly depends on the large permittivity peak, phenomenological coefficient and polarization.
The electrocaloric effect (ECE) in lead-free (Ba1−xSrx)(Sn0.05Ti0.95)O3 (BSSnT) (x = 0.05, 0.10, 0.15, 0.20) ceramics were investigated around room temperature using direct and indirect approaches. Results indicate that the maximum ECE occurs near the Curie temperature and slightly shifts towards high temperatures with the increasing applied electric field. The directly measured ECE is larger than that calculated using the Maxwell relation. The maximum electrocaloric strength ΔT/ΔE = 0.52 × 10−6 K m/V was obtained at T = 36 °C, with an adiabatic ΔT of 1.05 °C at 2 MV m−1. An analytic formula of electrocaloric strength (dT/dE) was deduced, via which the maximum dT/dE was estimated. The factors affecting the electrocaloric strength were discussed, and the experimental results were compared with those derived from the formula.
First-order magnetostructural transformation can be utilized to generate giant magnetocaloric effect for the magnetic refrigeration applications, but the intrinsic hysteresis always cripples the ...refrigeration efficiency. In this work, the strategy of lattice contraction was exploited to manipulate the thermal hysteresis and magnetocaloric response in the Ni-Co-Mn-In magnetocaloric alloys. Such strategy was effectuated by using Ge to replace In on account of the relatively smaller atomic radius of Ge, yielding a significant reduction in the thermal hysteresis. In a Ni46Co3Mn37In10Ge4 alloy with the combination of low thermal hysteresis of ∼4 K and large magnetization difference of 83.1 Am2kg−1 associated with the magnetostructural transformation, giant effective refrigeration capacity RCeff of 311 Jkg−1 and reversible entropy change ΔSM up to 22.8 Jkg−1K−1 were demonstrated by varying the field of 5 T. Besides, a large reversible adiabatic temperature change ΔTad of –3.0 K was also obtained by using a low field change of 1.5 T. Based on the displacement gradient tensor determined by the orientation relationship governing the martensitic transformation, it was presented that Ge substation for In effectively decreased the lattice misfit, thus lowering the elastic energy accompanying the structural transformation and the related transformation hysteresis.
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A comprehensive investigation of structural, microstructural, optical, electrocaloric, and energy storage properties of Ho-modified NBT-BT lead-free ceramics was conducted from room temperature to a ...high-temperature region. Rietveld refinement confirms the coexistence of dual-phase monoclinic (Cc) and tetragonal (P4mm) phases in Ho-modified NBT-BT ceramics. A prominent monoclinic distortion was found with increasing Ho composition up to x=0.02, and then an abrupt decrease for x=0.03 ceramic was noticed. Of particular importance is the composition of x = 0.02, which exhibits a high electrocaloric temperature change (ΔT) of 0.73 K @ E = 20 kV/cm at a temperature of 373 K, and an optimal high recoverable energy storage density (Wrec) of 1.8846 J/cm3 along with an efficiency 83% was achieved. The frequency dependence ac-conductivity study promotes the reduction of oxygen vacancies at room temperature and the dominance of single ionized oxygen vacancies at very high temperatures well above 300 °C. A small considerable increase in the energy bandgap values with the Ho3+ ion substitution in NBT-BT was observed. Under the excitation of 532 nm light, the two most prominent red fluorescence emission peaks were emitted, where the first emission band with weak intensity was observed at 657 nm which corresponds to the 5F5→5I8 transition, and a strong 2nd peak at 756 nm corresponds to the 5F4/5S2→5I7 level transition of the Ho3+ ion. These findings provide a feasible multifunctional property in the applications of power electronic devices with lead-free NBT-BT ceramics via rare-earth substitution.
In order to find a highly efficient, environmentally-friendly magnetic refrigerant, direct measurements of the adiabatic temperature change <inline-formula> <tex-math notation="LaTeX">\Delta T_{\text ...{adb}} </tex-math></inline-formula> are required. Here, in this work, a simple setup for the <inline-formula> <tex-math notation="LaTeX">\Delta T_{\text {adb}} </tex-math></inline-formula> measurement is presented. Using a permanent magnet Halbach array with a maximum magnetic field of 1.8 T and a rate of magnetic field change of 5 T/s, accurate determination of <inline-formula> <tex-math notation="LaTeX">\Delta T_{\text {adb}} </tex-math></inline-formula> is possible in this system. The operating temperature range of the system is from 100 to 400 K, designed for the characterization of materials with potential for room temperature magnetic refrigeration applications. Using the setup, <inline-formula> <tex-math notation="LaTeX">\Delta T_{\text {adb}} </tex-math></inline-formula> of a first-order and two second-order compounds have been studied. Results from the direct measurement for the first-order compound have been compared with <inline-formula> <tex-math notation="LaTeX">\Delta T_{\text {adb}} </tex-math></inline-formula> calculated from the temperature and magnetic field-dependent specific heat data. By comparing results from direct and indirect measurements, it is concluded that for a reliable characterization of the magnetocaloric effect (MCE), direct measurement of <inline-formula> <tex-math notation="LaTeX">\Delta T_{\text {adb}} </tex-math></inline-formula> should be adopted.
With the urgent need to explore low‐cost, high‐efficiency solid‐state refrigeration technology, the electrocaloric effects of ferroelectric materials have attracted much attention in the past ...decades. With the development of modern computing technology, the phase‐field method is widely used to simulate the evolution of microstructure at mesoscale and predict the properties of different types of ferroelectric materials. In this article, we review the recent progress of electrocaloric effects from phenomenological Landau thermodynamics theory to phase‐field simulation by discussing the microcosmic composition, mesoscopic domain structures, macroscopic size/shape, and external stimulus of strain/stress. More importantly, in searching for new ferroelectric electrocaloric cooling materials, it is possible to find materials whose free energy barrier height changes rapidly with temperature, such materials have a faster change rate with polarization temperature in terms of ferroelectric macroscopic properties, from them could get superior electrocaloric effects. We compile a relatively comprehensive computational design on the high performance of electrocaloric effects in different types of ferroelectrics and offer a perspective on the computational design of electrocaloric refrigeration materials at the mesoscale microstructure level.
La(Fe,Si)13H-based materials are considered to be one of the most promising room-temperature magnetic refrigerants. The intrinsic brittleness and relatively low thermal conductivity in La-Fe-Si-H ...alloys, however, have severely hindered its preparation, shaping and application. To solve this long-standing problem, in this work we propose a novel approach to fabricate stable La-Fe-Si-H blocks and plates by adding extra α-Fe as a reinforcing phase to enhance mechanical integrity. Much better bending strength compared to that in the stoichiometric composition has been observed in our dual phase La-Fe-Si-H magnetic refrigerants. Such novel Fe-rich plates can be exposed to 105 magnetic field cycles without losing mechanical integrity. In addition, a large and reproducible ΔTad of 5.4 K in 1.93 T and a thermal conductivity of 6 W/mK at room temperature have been obtained.
In the dual phase La-Fe-Si-H alloys, materials can be fabricated to the block shape, where the toughening α-Fe guarantees the mechanical integrity and offers significantly enhanced thermal conductivity. Display omitted
The current research focuses on analyzing the magnetic and magnetocaloric properties of REH2(RE=Gd,Tb,Dy) in a CaF2-like face-centered cubic system. Through the application of first-principles ...calculations and Monte Carlo simulations, the following physical parameters are determined: Adiabatic temperature change, isothermal entropy change, and relative cooling power (RCP). The magnetic moments of Gadolinium, Terbium, and Dysprosium calculated by the PWSCF method are 6.76μB, 5.74μB, and 4.65μB respectively, aligning well with experimental results. The compounds underwent a second-order phase transition from antiferromagnetic to paramagnetic at TN=21.7K, 17.6K, and 4.3K respectively for GdH2, TbH2, and DyH2. The isothermal entropy change (−ΔSMmax) reached a maximum value of −11.75J/kg.K, −12.47J/kg.K, and −12.87J/kg.K for GdH2, TbH2, and DyH2 under a magnetic field of 5T. We found also that the hydrogenation of rare earth reduces its magnetic performance while but it enhances its thermodynamic and mechanical stability.
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•The thermodynamic and mechanical stability of REH2(RE=Gd,Tb,Dy) compounds are investigated.•The REH2 compounds are metals with an antiferromagnetic state.•The magnetocaloric property values of REH2 compounds indicate that they are potential for low-temperature magnetic refrigeration applications.•Comparing the properties of Gd with REH2 compounds reveals the role of hydrogen in these materials.
