Caloric Materials Research Articles

Solid-state refrigeration: A comparison of the energy performances of caloric materials operating in an active caloric regenerator

The energy performances of an Active Caloric Refrigerator are reported in this paper. An ACR is tested under a vast number of solid-state refrigerants exhibiting one of the four main caloric effects considered for refrigeration (magnetocaloric, electrocaloric, elastocaloric and barocaloric effect). The analysis is performed numerically through a 2D model, experimentally validated, that can reproduce the behavior of an Active Caloric Regenerator. Temperature span, cooling power and coefficient of performance are the indexes through which the comparison is carried out. The tests are performed at a fixed AMR cycle frequency (1.25 Hz), in the temperature range 292–300 K, varying the mass flux in the range 150–250 kg s−1 m−2. The most promising caloric materials that have been tested as refrigerants are: Gd, Gd5Si2Ge2, LaFe11.384Mn0.356Si1.26H1.52, LaFe11.05Co0.94Si1.10 (magnetocaloric materials); P(VDF-TrFE-CFE)/BST polymer, 0.93PMN-0.07PT thin film, the Pb1-3x/2LaxZr0.85Ti0.15O3 with single and variable composition, PbTiO3, Pb0.8Ba0.2ZrO3, Pb0.97La0.02(Zr0.75Sn0.18Ti0.07)O3(electrocaloric materials); Cu68.13Zn15.74Al16.13, NiTi, PbTiO3 (elastocaloric materials); (NH4)2MoO2F4, MnCoGe0.99In0.01 (barocaloric materials). Among them, PLZT and in particular Pb0.97La0.02(Zr0.75Sn0.18Ti0.07)O3 show the best results, higher than every other caloric material tested, conferring to electrocaloric refrigeration globally the most promising behavior.

Simultaneously achieved large reversible elastocaloric and magnetocaloric effects and their coupling in a magnetic shape memory alloy

Large reversible caloric effects covering a broad temperature region are essential for high-efficiency and environment-friendly solid-state caloric refrigeration that can potentially replace the traditional vapor-compression-based cooling technology. Here, we report the simultaneously achieved large reversible magnetocaloric and elastocaloric effects in a Ni43Co6Mn40Sn11 magnetic shape memory alloy. A reversible near-room-temperature magnetic entropy change ΔSm of as high as 19.3 J kg−1 K−1 under 5 T was experimentally obtained and the corresponding adiabatic temperature change ΔTad was estimated to be 7.7 K. Meanwhile, a large reversible elastocaloric effect with a directly measured ΔTad up to 7.1 K was attained. The elastocaloric effect exhibits high cyclic stability with no apparent degradation during 380 cycles of loading and unloading. Furthermore, we propose and demonstrate the utilization of the multicaloric approach under the coupled uniaxial stress and magnetic field to enlarge the refrigeration temperature region of reversible caloric effects. By combining the reversible magnetocaloric and elastocaloric effects and the reversible multicaloric effect under the coupling of uniaxial stress and magnetic field in the hysteresis region, large reversible caloric effects covering a broad temperature region from 257 K to 383 K can be obtained. This study may pave the way for designing advanced caloric materials with cyclically stable and reversible large caloric effects and wide refrigeration temperature region for solid-state refrigeration.

Energy performances and numerical investigation of solid-state magnetocaloric materials used as refrigerant in an active magnetic regenerator

Magnetic is the most diffused, developed and evolved technique among solid-state cooling, a class of ecofriendly refrigeration systems employing solid-state caloric materials. Active Magnetic Regenerative refrigeration cycle (AMR), a Brayton based thermodynamical cycle, is the benchmark cycle for magnetic refrigeration. This paper aims to provide a map of energetic performances of an Active Magnetic Refrigerator by the development of a two-dimensional numerical model, whom replies the behaviour of one of the regenerators mounted in 8Mag, the experimental prototype of the first Italian Rotary Permanent Magnet Magnetic Refrigerator (RPMMR), mounting gadolinium. To this hope, through the model a performance map has been delineated and it has been investigated the behaviour of the AMR regenerator, mounting gadolinium, in order to explore the limit conditions of prototype working, in terms of cold-hot heat exchanger range, fluid flow rate and frequency. In a second step, the performance map has been extended to other MCE materials, possible candidates for magnetic refrigeration at room temperature.

Magneto-electric coupling in [formula omitted]-PZT multiferroic composite

In the paper there are presented magnetic, magnetoelectric, and magnetocaloric properties of the Fe48Rh52-PZT bilayer multiferroic composite close to room temperature. The maximum of adiabatic temperature change as well as the large magnetoelectric ordering around the antiferromagnetic-magnetic phase transition temperature of 315K for a magnetic field change of 0.62T is demonstrated. The application of a voltage across the bilayer structure shifts the metamagnetic transition by ∼4 K in cooling and by ∼3 K in heating. The magnitude of the magnetoelectric and magnetocaloric effects depends on the strain/stress in the magnetic layer induced by the piezoelectric one as a result of applying electric field. Such a finding can be successfully employed for controlling of the magnetic properties of caloric materials.

Material-based figure of merit for caloric materials

The efficient use of reversible thermal effects in magnetocaloric, electrocaloric, and elastocaloric materials is a promising avenue that can lead to a substantially increased efficiency of refrigeration and heat pumping devices, most importantly, those used in household and commercial cooling applications near ambient temperature. A proliferation in caloric material research has resulted in a wide array of materials where only the isothermal change in entropy in response to a handful of different field strengths over a limited range of temperatures has been evaluated and reported. Given the abundance of such data, there is a clear need for a simple and reliable figure of merit enabling fast screening and down-selection to justify further detailed characterization of those material systems that hold the greatest promise. Based on the analysis of several well-known materials that exhibit vastly different magnetocaloric effects, the Temperature averaged Entropy Change is introduced as a suitable early indicator of the material's utility for magnetocaloric cooling applications, and its adoption by the caloric community is recommended.

High-throughput search for caloric materials: the CaloriCool approach

The high-throughput search paradigm adopted by the newly established caloric materials consortium—CaloriCool®—with the goal to substantially accelerate discovery and design of novel caloric materials is briefly discussed. We begin with describing material selection criteria based on known properties, which are then followed by heuristic fast estimates, ab initio calculations, all of which has been implemented in a set of automated computational tools and measurements. We also demonstrate how theoretical and computational methods serve as a guide for experimental efforts by considering a representative example from the field of magnetocaloric materials.

Nucleation and dynamics of the metamagnetic transition in magnetocaloric La(Fe,Mn,Si)13

Refrigeration cycle rates of the order of 15 Hz are desirable for efficient solid state based magnetocaloric cooling, placing an upper bound on the combined magnetic transition and the heat transfer times of the order of tens of msecs. We use microcalorimetry and magnetometry to probe the transition dynamics as a function of magnetic field sweep-rate, sample size, thermal environment, temperature and hydrostatic pressure in LaFe11.74Mn0.06Si1.20. Although second order caloric materials follow the magnetisation or demagnetisation driving field without lag, here we show that the field driven evolution of the first-order phase transition in La(Fe,Si)13-based compounds show temporal dynamics on timescales that are significantly longer than tens of msecs, associated with the thermal linkage within the sample and the linkage to the external bath. We observe that features associated with the first nucleation of the transition are field sweep rate independent, and from measurements of the latent heat we infer that the barriers to magnetisation and demagnetisation are of different magnitude. Increasing the temperature or applying hydrostatic pressure reduces the dynamic effects, suggestive of diminishing first-order character of the transition under these conditions.

A Matter of Size and Stress: Understanding the First‐Order Transition in Materials for Solid‐State Refrigeration

Solid‐state magnetic refrigeration is a high‐potential, resource‐efficient cooling technology. However, many challenges involving materials science and engineering need to be overcome to achieve an industry‐ready technology. Caloric materials with a first‐order transition—associated with a large volume expansion or contraction—appear to be the most promising because of their large adiabatic temperature and isothermal entropy changes. In this study, using experiment and simulation, it is demonstrated with the most promising magnetocaloric candidate materials, La–Fe–Si, Mn–Fe–P–Si, and Ni–Mn–In–Co, that the characteristics of the first‐order transition are fundamentally determined by the evolution of mechanical stresses. This phenomenon is referred to as the stress‐coupling mechanism. Furthermore, its applicability goes beyond magnetocaloric materials, since it describes the first‐order transitions in multicaloric materials as well.

(Invited) The U.S. Department of Energy’s Energy Materials Network

Affordable, reliable, high performance materials and manufacturing technologies are key for most transformational technology advancements, including those in critical domestic energy applications. However, many materials discoveries in the laboratory either never reach widespread market deployment or spend decades in the development cycle at a cost of many tens or hundreds of millions of dollars. In response, the U.S. Department of Energy (DOE) has established the Energy Materials Network (EMN) to accelerate the materials-to-market process by better integrating the stages from materials discovery through manufacturing. The EMN is a network of national lab-led consortia that support both industry- and government-led research (e.g. CRADAs and FOA awards) on specific energy-related material challenges. The EMN framework facilitates industry stakeholder engagement to ensure that the research is immediately relevant, with high-impact commercial potential. To date, EMN consortia have been set up in the seven technology areas of: light-weight materials for transportation; precious-metal-free catalysts for fuel cells; water-splitting materials for hydrogen production; advanced catalysts for biomass conversion; new materials and designs for photovoltaic modules; advanced solid-state hydrogen storage materials; and advanced caloric materials for refrigeration. This presentation will describe the vision of the EMN as an enduring national resource, and discuss recent technical accomplishments in the current network of EMN consortia.

Materials with Giant Mechanocaloric Effects: Cooling by Strength

The search for materials with large caloric effects has become a major challenge in material science due to their potential in developing near room-temperature solid-state cooling devices, which are both efficient and clean, and that can successfully replace present refrigeration technologies. There are three main families of caloric materials: magnetocaloric, electrocaloric, and mechanocaloric. While magnetocaloric and electrocaloric materials have been studied intensively in the last few decades, mechanocaloric materials are only very recently receiving a great deal of attention. The mechanocaloric effect refers to the reversible thermal response of a solid when subjected to an external mechanical field, and encompasses both the elastocaloric effect, corresponding to a uniaxial force, and the barocaloric effect, which corresponds to the response to hydrostatic pressure. Here, the state of the art in giant mechanocaloric effects is reviewed and a critical analysis of the thermodynamic quantities that characterize the major families of barocaloric and elastocaloric materials is provided. Finally perspectives for further development in this area are given.

On entropy change measurements around first order phase transitions in caloric materials

In this work we discuss the measurement protocols for indirect determination of the isothermal entropy change associated with first order phase transitions in caloric materials. The magneto-structural phase transitions giving rise to giant magnetocaloric effects in Cu-doped MnAs and FeRh are used as case studies to exemplify how badly designed protocols may affect isothermal measurements and lead to incorrect entropy change estimations. Isothermal measurement protocols which allow correct assessment of the entropy change around first order phase transitions in both direct and inverse cases are presented.

Elastocaloric Effect in Carbon Nanotubes and Graphene.

Carbon nanotubes are famous for their many extraordinary properties. We use a thermodynamical approach, experimental data from the literature, and atomistic simulations to reveal one more remarkable property of the carbon nanotubes that has so far been overlooked. Namely, we predict the existence of very large elastocaloric effect that can reach up to 30 K under moderate loads. Potentially even larger values could be achieved under extreme loads, putting carbon nanotubes in the forefront of caloric materials. Other remarkable features of the elastocaloric effect in carbon nanotubes include linearity of elastocaloric temperature change in applied force (compressive or stretching), very weak dependence on the temperature, and an absence of hysteresis. Such features are extremely desirable for practical applications in cooling devices. Moreover, a similarly large elastocaloric effect is predicted for the graphene. The prediction of a large elastocaloric effect in carbon nanotubes and graphene sets forward an unconventional strategy of targeting materials with moderate caloric responses but the ability to withstand very large loads.

Elastocaloric cooling processes: The influence of material strain and strain rate on efficiency and temperature span

Abstract

Preface to Special Topic: Caloric Materials

Preface to Special Topic: Caloric Materials

Some strategies for improving caloric responses with ferroelectrics

Many important breakthroughs and significant engineering developments have been achieved during the past two decades in the field of caloric materials. In this review, we address ferroelectrics emerging as ideal materials which permit both giant elastocaloric and/or electrocaloric responses near room temperature. We summarize recent strategies for improving caloric responses using geometrical optimization, maximizing the number of coexisting phases, combining positive and negative caloric responses, introducing extra degree of freedom like mechanical stress/pressure, and multicaloric effect driven by either single stimulus or multiple stimuli. This review highlights the promising perspective of ferroelectrics for developing next-generation solid-state refrigeration.

Solid-state cooling with caloric materials

The drive to replace volatile liquid refrigerants is gaining steam, with potentially disruptive technologies on the horizon.

Residual stress induced stabilization of martensite phase and its effect on the magnetostructural transition in Mn-rich Ni-Mn-In/Ga magnetic shape-memory alloys

The irreversibility of the martensite transition in magnetic shape memory alloys (MSMAs) with respect to external magnetic field is one of the biggest challenges that limits their application as giant caloric materials. This transition is a magneto-structural transition that is accompanied with a steep drop in magnetization (i.e., 'delta M') around the martensite start temperature (Ms) due to the lower magnetization of the martensite phase. In this communication, we show that 'delta M' around Ms in Mn rich Ni-Mn based MSMAs gets suppressed by two orders of magnitude in crushed powders due to the stabilization of the martensite phase at temperatures well above the Ms and the austenite finish (Af) temperatures due to residual stresses. Analysis of the intensities and the FWHM of the x-ray powder diffraction patterns reveals stabilized martensite phase fractions as 97, 75 and 90% with corresponding residual microstrains as 5.4, 5.6 and 3% in crushed powders of the three different Mn rich Ni-Mn alloys, namely, Mn1.8Ni1.8In0.4, Mn1.75Ni1.25Ga and Mn1.9Ni1.1Ga, respectively. Even after annealing at 773 K, the residual stress stabilised martensite phase does not fully revert to the equilibrium cubic austenite phase as the magneto-structural transition is only partially restored with reduced value of 'delta M'. Our results have very significant bearing on application of such alloys as inverse magnetocaloric and barocaloric materials.

New developments in caloric materials for cooling applications

Caloric materials are in the spotlight as candidates for future environmentally friendly cooling technologies. We describe stimulating recent developments in the three caloric strands that are now being studied collectively, namely magnetocaloric, electrocaloric and mechanocaloric (elastocaloric or barocaloric) effects.

Caloric materials near ferroic phase transitions.

A magnetically, electrically or mechanically responsive material can undergo significant thermal changes near a ferroic phase transition when its order parameter is modified by the conjugate applied field. The resulting magnetocaloric, electrocaloric and mechanocaloric (elastocaloric or barocaloric) effects are compared here in terms of history, experimental method, performance and prospective cooling applications.

Barocaloric effect in metamagnetic shape memory alloys

AbstractWe report on calorimetric measurements under hydrostatic pressure in a series of composition related metamagnetic shape memory alloys. We show that metamagnetic shape memory alloys exhibit a barocaloric effect whose magnitude compares well to the magnetocaloric effect exibited by this kind of alloys. While in metamagnetic alloys the magnetocaloric effect is inverse, the barocaloric effect has been found to be conventional. The values obtained for the pressure‐induced entropy changes at moderate pressures are in the range of those reported for giant caloric materials.