Electrocaloric Effect Research Articles

Electrocaloric effects in ferroelectrics and multiferroics from first principles

Significant enhancement of the negative electrocaloric effect in Mn-doped PbHfO3 films

Enhancement of the energy storage and electrocaloric effect performances in 0.4 BCZT–0.6 BSTSn medium-entropy ceramic prepared by sol-gel method

Abstract Research into electrocaloric materials has grown within the past two decades. After a brief introduction where we give a sense of this growth, we define electrocaloric effects by starting simplistically, making refinements, and including mechanistic information. We then describe the history of the field, explaining how the focus switched from bulk materials to thin films to multilayer capacitors, and how prototype coolers and measurements were pioneered. After that, we describe the current activity, which includes detailed material maps, improved metrology, and improved prototypes. Last, we comment on future directions, and the challenges that must be overcome for applications. In order for the reader to establish a holistic overview of electrocalorics, we have tended to avoid presenting chemical formulae, equations and metrics, all of which are readily available in the cited references. Graphical abstract

The rapid evolution of functional oxides has revolutionized modern condensed matter physics and materials engineering, driven by their intricate spin-lattice-charge-orbital couplings and diverse functional properties. Among these, relaxor antiferroelectrics represent a prominent class of materials, distinguished by their unique second-order-like field-induced phase transitions and complex domain architectures. Unlike conventional antiferroelectrics, relaxor antiferroelectrics exhibit dynamic disorder and structural heterogeneity, offering unprecedented opportunities for electromechanical functionalities. This review systematically traces the evolution of antiferroelectrics from bulk to thin-film architectures and presents a critical analysis of state-of-the-art characterization techniques, such as advanced X-ray diffraction, scanning probe microscopy, and atomic-resolution transmission electron microscopy. A central focus lies in establishing design principles for high-performance relaxor antiferroelectric films, including interface engineering, structural heterogeneity, and chemical modification. The review further evaluates emerging energy-related applications spanning energy-storage capacitors, the electrocaloric effect, thermal switching, etc. Additionally, contemporary challenges and future prospects are highlighted, aiming to underscore novel research directions that will propel the advancement of antiferroelectrics and device designs. It is the earnest hope that this review will catalyze collaborative explorations into the unknown, fostering groundbreaking advancements in relaxor antiferroelectrics.

Abstract Searching for material with a high electrocaloric (EC) response over a wide temperature range near the ambient temperature is a priority area of research in solid-state refrigeration technology. The perovskite system with cationic vacancies could allow tuning the EC parameters over a wide temperature range via the associated entropy change. In this context, La-substituted BaTiO3 has been investigated, with a focus on introducing cationic vacancies to dilute the ferroelectric system with a primary objective of simultaneously tailoring the Curie temperature (T C) closer to room temperature (∼300 K) and stabilizing it over a wide temperature span. The analysis of Raman and x-ray photoelectron spectroscopy confirms the formation of cationic vacancies. Consequently, a diffused ferroelectric phase transition with weak relaxor feature is confirmed by modified-Curie–Weiss law and Vogel–Fulcher fitting analysis. As a result, the observed shift in ferroelectric transition temperature from 400 K to 290 K upon La-substitution is correlated to the effect of vacancies in the perovskite structure. In addition, the EC studies demonstrated the tuning of adiabatic temperature change ( Δ T) spanning over a wide temperature range ( Δ T span ) from 5 K to 45 K, covering the room temperature. Tuning of Δ T span with a moderate Δ T max values highlight the La-substituted sample’s potential in cooling applications with relative cooling power values ranging from 34.92 K2 to 67.58 K2. These studies provide insights into tuning the EC parameters by inducing cationic vacancies in the perovskite-based ferroelectric oxides.

The increasing demand for higher operating speeds and greater integration densities in electronic devices has made heat dissipation one of the most critical challenges for next-generation technologies. This challenge has driven extensive efforts aimed at achieving a giant electrocaloric effect in ferroelectrics for high-efficiency cooling. Here, we propose a defect dipole engineering strategy to manipulate the polarization behavior of ferroelectric ceramics, leading to superior electrocaloric effect. By incorporating Sm and Li ions, the (SmBȧ-LiBa') defect dipoles enhance the polarizability of BaTiO3. Simultaneously, these dipole defects increase the carrier activation energy, effectively mitigating the inherent trade-off between high breakdown strength and high polarization, thereby allowing the application of a high electric field to fully activate the electrocaloric potential. As a result, defect dipole engineering enables BaTiO3 to achieve a remarkable electrocaloric effect over a wide temperature range, achieving a high temperature change of 2.7 K at 70 °C- typical for integrated circuits.

Electrocaloric effect referring to reversible temperature change (ΔT) under electrical excitation provides a promising alternative for next-generation thermal management. The ΔT essentially derives from the polarization change of polar system. However, conventional engineering hardly synchronizes large and flexible polarization change, so that large ΔT and high electrocaloric strength cannot realize concurrently. Herein, we propose a novel design strategy of multiscale engineering to boost the polar entropy of system, by which the large and flexible polarization change can be offered synchronously, availing large ΔT under a low driving field. The envision is validated in a heterogeneous Ba(Ti1-xSnx)O3 system, where the different Ba(Ti1-xSnx)O3 granules are mixed to enhance polarization heterogeneity of system. A large ΔT of 1.5 K and a high electrocaloric strength of 0.375 K mm kV−1 are achieved under a low driving field of 40 kV cm−1. Meanwhile, the substantial ΔT of more than 1.2 K is maintained within 30–50 °C. Our strategy provides a new paradigm for engineering electrocaloric material properties and can be expected for the design of other high-performance ferroelectrics.

Geometric mismatch of chain lengths enhancing the electrocaloric effect in PVDF

The electrocaloric effect of a ferroelectric materialis an effectivetechnique for solid-state refrigeration. Although the peak value ofthe adiabatic temperature change (ΔT) due tothe electrocaloric effect in normal ferroelectrics is found near theCurie point (Tc), ferroelectrics witha diffuse phase transition are always desirable due to their widetemperature span of ΔT. In this work, the electrocaloriceffect in sustainable Pb-free weak relaxor ferroelectrics, (1 – x)­Ba­(Zr0.2Ti0.8)­O3 – x(Ba0.7Ca0.3)­TiO3 (x = 0.19 and 0.21), with diffuse phase transition is reported.The diffuseness of each composition is determined based on the fittingof the temperature-dependent dielectric permittivity data to the Lorenz-typequadratic law. Interestingly, the maxima of ΔT of the compositions are observed at much higher temperatures thanthe temperature at maximum dielectric permittivity (Tm) and freezing temperature (Tf), which work as the effective Tc ofa relaxor ferroelectric. The wide temperature span (40 K) and highΔT (0.8 K) of the x = 0.19composition show the potential of this material for solid-state refrigerationapplications. Moreover, the effects of diffuse phase transition onΔT and its temperature span are discussed in(1 – x)­Ba­(Zr0.2Ti0.8)­O3 – x(Ba0.7Ca0.3)­TiO3-based ferroelectrics, which will help todesign Pb-free electrocaloric materials with a diffuse phase transitionfor a wide working temperature range.

Abstract Solid‐state cooling and energy harvesting via the pyroelectric (PEE) and electrocaloric (ECE) effects in ferroelectric thin films can be boosted by directional enhancement, though its origin is unclear. We performed direct hysteresis measurements of pyrocurrent ( I p​ ) and ECE‐induced temperature change versus bias in 1 µm‐thick Pb(Zr0.65Ti0.35)O3 ​ capacitors. Both loops exhibit pronounced asymmetries along voltage and response axes. Applying DC voltage offsets isolates a residual I p‐axis shift, revealing non‐switchable polarization. Bipolar triangular pulses convert this component to switchable polarization, confirming defect‐induced domain pinning. After 100 pulses, aging causes the switchable contribution to decay while the non‐switchable component remains nearly constant, indicating partial repinning. The evolution of the loop‐shift voltage correlates with the non‐switchable/switchable ratio, showing that imprint arises from pinned domains. These findings highlight the key role of non‐switchable polarization in PEE and ECE and suggest controlled poling and defect engineering as strategies for optimizing directional response.

Enhanced electrocaloric effect in lead-free NBiSLKTSn doped BaTiO3 ceramics via high-entropy doping and an empirical relation between the ECE ΔS (ΔT) and Pm2/εm

Investigation of electrocaloric effect and scaling behavior with correlation of structural, electrical, and impedance properties in Sn-substituted NBT–BT ceramics near MPB

The electrocaloric (EC) effect holds irresistible attraction for personalized thermoregulation, since it can actively optimize bidirectional individual thermophysiological comfort with ultralow energy consumption. However, the practical application of EC polymer-based personalized thermoregulation has been severely limited by its high driving voltage. Here, a multilayer EC polymer stack with a layer thickness of 1 μm is constructed, realizing an observable adiabatic temperature change (ΔT) under safe driving voltage. The practicality of this EC polymer stack has been consolidated by driving two EC polymer stacks with one AA battery on the human hand. By analogy, 625 EC polymer stacks that are capable of covering the whole trunk of the human body with a ΔT of 4 K could be theoretically driven by only one AA battery. Featuring a low driving voltage, compact wearable design, and ultralow energy consumption, this active bidirectional multilayer EC polymer stack could partially bridge the gap between the EC effect and personalized thermoregulation.

The electrocaloric effect of ferroelectrics holds great promise for solid-state cooling, potentially replacing traditional vapor-compression refrigeration systems. However, achieving adequate electrocaloric cooling capacity at room temperature remains a formidable challenge due to the need for a high intrinsic electrocaloric effect. While barium titanate ceramic exhibits a pronounced electrocaloric effect near its Curie temperature, typical chemical modifications to enhance electrocaloric properties at room temperature often reduce this intrinsic electrocaloric effect. Herein, a structural design is introduced for barium titanate-based ceramics by incorporating isovalent cations. This leads to a well-ordered local structure that decreases the Curie temperature to room temperature while preserving a sharp phase transition, enabling a large dielectric constant and tunable polarization. This design achieves a remarkable electrocaloric strength of ~1.0 K·mm/kV, surpassing previous reports. Atomic-resolution structural analyses reveal that the presence of multiscale nanodomains (from ~10 nm to >100 nm), and the dipole polarization distribution with gradual dipole rotation enable rapid phase transition and facile polarization rotation, accounting for the giant electrocaloric response. This work provides a strategy for achieving a strong intrinsic electrocaloric effect in ferroelectrics near room temperature and offers key insights into the microstructure landscapes driving this enhanced electrocaloric effect.

Enhanced electro-caloric effect and broad temperature span in lanthanum-modified lead zirconate titanate based on a multilayer ceramic approach

ABSTRACTThe electrocaloric effect (ECE) in ferroelectric materials is considered a candidate for solid‐state refrigeration technology due to its merits of environmental friendliness, high integration, and low energy consumption. Herein, a series of poly(vinylidene fluoride‐trifluoroethylene‐chlorotrifluoroethylene) (P(VDF‐TrFE‐CTFE)) terpolymers are synthesized by using the hydrogenation method and are then compounded with the conductive filler graphene nanosheets (GR) to obtain GR/P(VDF‐TrFE‐CTFE) composites. Benefiting from the large specific surface area of GR, the interfacial polarization of GR/P(VDF‐TrFE‐CTFE) composite is significantly improved, contributing to a high maximum polarization (~2.35 μC/cm2). As such, a maximum adiabatic temperature change (ΔT) of ~4.22 K (at 320.6 K) is realized in GR/P(VDF‐TrFE‐CTFE) composite with 0.05 wt% GR at a low electric field of 50 MV/m, which is an improvement of 51.8% compared to the pure P(VDF‐TrFE‐CTFE) (ΔT is ~0.08 K at 320.5 K). This result indicates the latent capacity of GR fillers in increasing the ECE of ferroelectric polymer materials, providing a new approach for designing the optimal filler/polymer combination suitable for solid‐state refrigeration.

Electrocaloric effect refers to an induced adiabatic temperature change and/or isothermal entropy change that results from variations in electric polarization within a dielectric material under an applied electric field. The isothermal entropy change ΔS contains dipole entropy change ΔSdip due to dipole alignment and phonon entropy change ΔSph due to intrinsic structure response. As the temperature increases, the typical ferroelectric material BaTiO3 undergoes a series of phase transitions from rhombohedral, orthorhombic, and tetragonal ferroelectric phase to cubic paraelectric phase. Moreover, the phase transition mode is the coexistence of displacive and order–disorder type. Prior studies have predominantly focused on the electrocaloric effect in the displacive model. Here, we thoroughly investigate the phonon entropy change ΔSph and phonon temperature change ΔTph based on both phase transition models and three ferroelectric phases and evaluate their contribution to the total electrocaloric effect. Our findings reveal that ΔTph contributes up to 45% of the total electrocaloric effect in the rhombohedral phase, representing the greatest average contribution among the phases. Furthermore, we employ the phonon density of states to elucidate the mechanisms of ΔSph under external electric fields. We also provide insights into the dynamic charge transfer of strongly coupled atoms under electric field through Born effective charge.

In the search for alternative, environmentally friendly refrigeration technologies, caloric effects play an important role. Over the past years, liquid crystals have emerged as promising caloric materials. Here, we present a molecular simulation study of the electrocaloric and magnetocaloric effect in liquid crystals exhibiting a nematic-isotropic phase transition. The indirect approach for determining the caloric response is used in combination with molecular dynamics simulations based on the Gay-Berne model. The simulations confirm that the largest response is present at temperatures just above the phase transition and predict the magnitude of the electrocaloric response to be ∼1.6 kJ/kg for an applied electric field of 1600kV/cm. A much weaker magnetocaloric response is predicted, ∼0.4 kJ/kg for an applied magnetic field of 200T, indicating that electric fields are much more promising for use in applications than magnetic fields.

Textured ceramics exhibit a reduced coercive field, and when aligned in the same direction as the spontaneous polarization, they enhance the adiabatic temperature change (ΔT ) of the material. In this paper, we employ a polycrystalline phase-field model to analyze the solid solution Ba0.8Sr0.2TiO3 (BST80) with a <001> orientation, alongside randomly oriented polycrystals, aiming to investigate the influence of texturing on the electrocaloric effect (ECE) performance. We examine six distinct groups characterized by varying grain orientation angles for the randomly oriented polycrystals for hysteresis loop calculations. Utilizing Maxwell's relations, we compute the ECE for the randomly oriented BST80 polycrystal and the <001>-textured BST80 polycrystal across different electric field strengths. The findings indicate that the ∆T achieved with the <001>-textured BST80 polycrystal surpasses that of the randomly oriented BST80 polycrystal. Furthermore, the temperature at which the maximum ΔT occurs for the <001>-textured BST80 polycrystal is observed to be shifted to higher values compared to the randomly oriented variant. The observed enhancement of ECE in BST80 polycrystalline ceramics due to texturing offers valuable insights and foundational knowledge for future theoretical and experimental investigations.