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Applied materials research and testing often involve measurements of material properties such as dielectric permittivity, impedance, piezoelectric coefficient, and pyroelectric current under non-ambient conditions and a controlled atmosphere. This requires simultaneous operation of multiple types of equipment and a controlled atmosphere for non-ambient conditions with computer-controlled data collection and operation. Here, we present the design and fabrication of a cost-effective measurement probe and measurement furnace with a capability of 1000°C under a controlled gas atmosphere. The setup, when used in tandem with an LCR meter or a source measure unit, can perform impedance and pyroelectric current measurements up to a temperature of 1000°C under a controlled atmosphere. We demonstrate the measurement capabilities in well-known ferroelectrics and oxide ion conductors including BaTiO3, (La0.9Sr0.1)(G0.9Mg0.1)O3-δ, Na0.5Bi0.5TiO3, and Pb(Zr, Ti)O3. [ABSTRACT FROM AUTHOR]

Ferroelectricity in biological system has been anticipated both theoretically and experimentally over the past few decades. Claims of ferroelectricity in biological systems have given rise to confusion and methodological controversy. Over the years, a “loop” of induced polarization in response to a varying applied electrical field and a consequent polarization reversal has prompted many researchers to claim ferroelectricity in biological structures and their building blocks. Other observers were skeptical about the methodology adopted in generating the data and questioned the validity of the claimed ferroelectricity as such, “loop” can also be obtained from linear capacitors. In a paper with somewhat tongue-in-cheek title, Jim Scott showed that ordinary banana peels could exhibit closed loops of electrical charge which closely resemble and thus could be misinterpreted as ferroelectric hysteresis loops in barium sodium niobate, BNN paraphrasing it as “banana”. In this paper, we critically review ferroelectricity in biological system and argue that knowing the molecular and crystalline structure of biological building blocks and experimenting on such building blocks may be the way forward in revealing the “true” nature of ferroelectricity in biological systems.

Abstract Complex oxides exhibit a wide range of fascinating functionalities, such as ferroelectricity, piezoelectricity, and pyroelectricity, which are indispensable for cutting‐edge electronics, energy, and information technologies. The intriguing physical properties of these complex oxides arise from the complex interplay between lattice, orbital, charge, and spin degrees of freedom. Here, it is reviewed how electromechanical properties can be achieved/improved by artificially breaking the symmetry of centrosymmetric oxides via engineering thermodynamic variables such as stress, strain, electric field, and chemical potentials. The mechanisms that have been utilized to break the inherent symmetry of conventional materials that lead to novel functionalities and applications are explored. It is highlighted that access to “hidden phases,” which otherwise are prohibited, could uncover opportunities to host exotic properties, such as piezoelectricity, pyroelectricity, etc. This review not only reports how to engineer intrinsically nonpolar and centrosymmetric oxides for emergent properties, but also has implications for manipulating polar functional materials for better performance.

Lithium niobate has emerged as a promising platform for integrated quantum optics, enabling efficient generation, manipulation, and detection of quantum states of light. However, integrating single-photon detectors requires cryogenic operating temperatures, since the best performing detectors are based on narrow superconducting wires. While previous studies have demonstrated the operation of quantum light sources and electro-optic modulators in LiNbO _3 at cryogenic temperatures, the thermal transition between room temperature and cryogenic conditions introduces additional effects that can significantly influence device performance. In this paper, we investigate the generation of pyroelectric charges and their impact on the optical properties of lithium niobate waveguides when changing from room temperature to 25 K, and vice versa. We measure the generated pyroelectric charge flow and correlate this with fast changes in the birefringence acquired through the Sénarmont-method. Both electrical and optical influence of the pyroelectric effect occur predominantly at temperatures above 100 K.

A nonlinear thermodynamic analysis is adopted to study the electrocaloric effect of B a x S r 1 − x Ti O 3 (BST) solid solutions. The results reveal that the location of maximum adiabatic temperature change Δ T can be shifted from a high temperature to room temperature via tuning chemical composition x. Comparing the electrocaloric properties of BST with those values reported in other electrocaloric materials, it is found that BST with x = 0.7 shows a large electrocaloric response over a broad temperature range near room temperature and possesses a large electrocaloric strength Δ T / Δ E ∼ 1.978 × 10 − 6 K m/V due to a significant change in polarization with respect to temperature. This suggests that BST with high electrocaloric performance has potential for practical cooling applications. [ABSTRACT FROM AUTHOR]

Dielectric spectroscopy of a SrTiO 3 single crystal over a broad range of microwave frequency using quasi T E m , 1 , 1 and quasi T M m , 1 , 1 modes reveals crystal asymmetry from typical measurement of Q-factor, transmission, or frequency characteristics in continuous cooling down to a few Kelvin. The properties of the modes due to the crystal asymmetry are validated by implementing a quasiharmonic phonon approximation. The observed ferroelectric phase transition temperature is around 51 K, and quantum-mechanical stabilization of the paraelectric phase arises below 5 K with very high permittivity. Also, an antiferrodistortive transition was indicated at 105 K. Landau's theory of correlation length supports the observation of an extra-loss term so the transition may be identified near the Q-factor maxima or transmission maxima depending on the other loss terms present in the cavity. Thus, the ferroelectric phase transition with respect to temperature is identified when its extra-loss term causes a discontinuity or deviation in the derivative of the temperature characteristic near the minimum of total cavity loss (maximum Q-factor or maximum transmission temperature characteristic). This temperature is confirmed by transmission amplitude variation of quasi T E 2 , 1 , 1 under 200 V dc electric field showing the existence of the soft-mode. These measurements support a typical polarization model and explicit temperature dependency of the soft-mode incorporating an imaginary frequency. [ABSTRACT FROM AUTHOR]

Negative environmental consequences of traditional cooling technologies have spurred the development of newly emerged green cooling devices rooting in electrocaloric effect (ECE). The relaxor ferroelectrics represented by BaZrTiO3 ceramics are being actively explored as a promising candidate for constructing ECE cooling devices. However, the reported electrocaloric (EC) response of BaZrTiO3 is still limited, particularly under low and moderate electric fields, which greatly inhibits its practical application. In this work, we propose an interfacial coupling modulation approach to enhance the EC response of BaZrTiO3 by introducing composition homogeneous and composition gradient multilayered structures. A systematic work was performed to study the dielectric, ferroelectric, and EC performances of BaZrTiO3 multilayered ceramics consisting of BaZr0.20Ti0.80O3 and/or BaZr0.17Ti0.83O3. It was found that the optimized BaZr0.17Ti0.83O3/BaZr0.20Ti0.80O3 bilayered films displayed the maximum EC response of 4.1 K under 10 MV m−1 at ambient conditions, corresponding to a high level of the coefficient of performance up to 18.33. The results demonstrate the efficiency of interfacial coupling modulation in boosting the EC response of relaxor ferroelectric ceramics, opening up an avenue to explore advanced electrocaloric systems with a giant electrocaloric effect. [ABSTRACT FROM AUTHOR]

An effect of Rhodamine 6G dye introduced into vinylidenefluoride and tetrafluoroethylene copolymer on a number of its structural and electrical characteristics has been detected. It was shown that at film crystallization, the inserted dopant shifts the equilibrium distribution of isomers to the side of increasing concentrations of chains with the conformation of a planar zigzag. The dye introduced strongly increases ac conductivity, especially at high electric fields. The investigation of high voltage polarization under bipolar external field conditions shows slow switching of gigantic current which is observed at fields lower than coercive ones. The estimation of the charge density indicates the non-ferroelectric nature of the phenomenon observed. The analysis of the data shows that in the system, Maxwell–Wagner relaxation processes take place, which lead to the space charge formation in the polymer matrix. It is established that current switching observed must be attributed to the relaxation of the space charge field. [ABSTRACT FROM AUTHOR]

This work has been carried out to investigate the poling temperature and poling field dependences of pyroelectric and dielectric properties of ⟨ 111 ⟩ oriented Mn-doped 0.72Pb(Mg1/3Nb2/3)O3-0.28PbTiO3 single crystals. Poling treatments are implemented at 25 °C, 90 °C, and 120 °C with DC poling electric fields of 1, 2, 3, and 4 times the corresponding coercive field, respectively. The correlation between ferroelectric domain transition and pyroelectric properties is investigated. The optimized pyroelectric and dielectric performances with the highest pyroelectric coefficient p and the lowest dielectric loss tan δ, as well as the optimized figures of merit, are achieved by poling samples at 90 °C in this study, instead of those conventionally poled at nearly Curie temperature (120 °C). Moreover, excellent long-term performances of 90 °C poled Mn-PMN-0.28PT crystals are disclosed over a 30-day range. [ABSTRACT FROM AUTHOR]

Phase transition is expected in designing high-performance electrocaloric effect (ECE). However, hidden antiferroelectricity in NaNbO3-based ceramics complicates ECE evolution as compared to conventional ferroic materials. Therefore, a NaNbO3−xBi0.5Li0.5TiO3 (x = 0.08, 0.10, and 0.12) system is introduced to explore ECE performance in P (Pbma), Q (P21ma), and R (Pnma) phases since a Bi0.5Li0.5TiO3 dopant plays a Janus role in stabilizing ferroelectric Q (x = 0.08 and 0.10) and inducing the antiferroelectric (AFE) relaxor R phase (x = 0.12). Rietveld refinement reveals a phase structure change from the P/Q to R state. Bi0.5Li0.5TiO3 addition makes a downshift of P-to-R transition temperature accompanied by an increase in relaxation property, as certified by dielectric analysis/piezoelectric force images, in situ XRD/Raman spectra, and ferroelectric tests. Additionally, a square P–E loop evolves into less-sharp and finally changes into a slant one with increasing Bi0.5Li0.5TiO3 content. ECE is directly measured, and its peak value increases from 0.15 K for x = 0.08 and 0.21 K for x = 0.10 and finally to 0.11 K for x = 0.12 composition. Interestingly, dual ECE peaks appear in x = 0.10, and it is probably contributed by R relaxor polar nanodomains. This work not only clarifies actual ECE behavior in AFE orthorhombic (P/R) NaNbO3-based ceramics but also fulfills understandings of AFE P-to-R transitions in modulating ECE. [ABSTRACT FROM AUTHOR]

Electrocaloric effect (ECE) offers an efficient and environmentally friendly route for solid-state cooling. Either positive or negative ECE could exhibit a large adiabatic temperature change (ΔT). Compared to the positive electrocaloric response, the investigation of negative ECE is lagging behind, largely due to the fact that its origin is still elusive. In this work, the negative ECE behavior of conventional ferroelectric thin films, namely 0.94(Bi0.5Na0.5)TiO3-0.06BaTiO3 (BNBT), was studied. A remarkable ΔT of −26.1 K was acquired near 160 °C under a moderate electric field of 875 kV/cm, attributing to the ferroelectric phase transition in the polar nanoregions from rhombohedral (R3c) to tetragonal (P4bm), as confirmed by temperature-dependent dielectric permittivity, Raman spectra, and x-ray reciprocal space mapping. The BNBT thin film presents a high electrocaloric coefficient (ΔT/ΔE) of 0.0298 K cm kV−1, transcending that of the most reported negative electrocaloric response of thin films. [ABSTRACT FROM AUTHOR]

We report on a direct measurement method for electrocaloric effects, the heating/cooling upon application/removal of an electric field in dielectric materials, based on a lock-in thermography technique. By use of sinusoidal excitation and multi-harmonic detection, the actual temperature change can be measured by a single measurement in the frequency domain even when the electrocaloric effect shows a nonlinear response to the excitation field. We demonstrated the method by measuring the temperature dependence of the electric-field-induced temperature change in two Sr-doped BaTiO3 systems with different ferroelectric-paraelectric phase transition temperatures, where we introduce the procedure for extracting the pure electrocaloric contribution free from heat losses and Joule heating due to leakage currents. This method can be used irrespective of the type of dielectric material and enables simultaneous estimation of the polarization change and power dissipation during the application of an electric field, making it a convenient imaging measurement method for the electrocaloric effect. [ABSTRACT FROM AUTHOR]

A figure of merit for assessing the cooling efficiency of electrocaloric (EC) materials is defined, where the caloric properties are taken into account jointly with the material's losses. Using a specifically developed measurement setup, based on flexible thermistances, the caloric effect and the losses are directly measured on P(VDF-TrFE-CFE) electrocaloric polymer films. The data are used, jointly with our figure of merit, to extrapolate the cooling efficiency to be expected, under actual working conditions, from the studied EC material. Dielectric losses emerge as a major limiting factor for achieving the needed cooling performance. This finding shows that, beside the research for huge caloric response, material loss reduction has to be considered a key objective for researching an optimal EC refrigerant for cooling applications. Eventually, some strategies toward loss reduction are outlined. [ABSTRACT FROM AUTHOR]

Self-actuating ferroelectric cooling technology have drawn increasing attention for its extensive application prospect, where simultaneous enhancement of electrocaloric effects (ECE) and electrostrain (ES) in ferroelectric materials is necessary prerequisites for the efficient operation of the cooling system. In this work, we proposed a self-actuating dual cooling cycle system combining the positive and negative ECE/ES effect, and further confirmed its feasibility in 0.7 Pb(Mg 1/3 Nb 2/3)O 3 -0.3PbTiO 3 (PMN-30PT) single crystal via bipolar electric field regulation. A suitable reverse electric field can generate negative ECE and ES simultaneously due to the reversible polarization rotation, whereas a high reverse electric field will lead to a serious perform loss as a result of emergent irreversible polarization jumping. The optimal reverse electric field (-E op) can enhance the total ECE and ES by 31% and 17% respectively, whose effective combination can significantly improve the cooling capacity of the self-actuating cooling system. Moreover, compared to traditional P - E and/or I - E measurements, we proposed a more applicable and precise method to determine the -E op under square-wave DC electric field, i.e. capacitance-voltage measurement. Our work not only provides new ideas for improving the ECE and ES of the ferroelectric materials, but also promotes the design of ferroelectric cooling systems. [ABSTRACT FROM AUTHOR]

The evolution of the dielectric hysteresis loops shape during heating of PMN-0.28PT single crystals possessing rhombohedral symmetry at room temperature was studied in the temperature range from room temperature to 200 °C. Revealed formation of the triple and double dielectric hysteresis loops in the relaxor phase upon switching by an electric field was explained by the influence of depolarizing fields arising at the interface of non-polar inclusions, and by the ineffective screening of polar clusters forming during transition through a percolation threshold, correspondingly. Further size decrease in the polar clusters due to heating led to their transformation to polar nanoregions. [ABSTRACT FROM AUTHOR]

Recently, the high efficient and environment–friendly electrocaloric cooling technology has become a hot topic. Unfortunately, the single process and extreme conditions have greatly limited its application. Due to the similar perovskite structure, Bi 5 Ti 3 FeO 15 and BiFeO 3 were selected to fabricate mesoscopic composites in this work to realize the double consecutive cooling effect. We propose that the non–collinear interfacial polarization is the origin of near room temperature electrocaloric cycling refrigeration. The electrons are trapped at the Bi 5 Ti 3 FeO 15 /BiFeO 3 interfacial potential well, where the electrons possess discontinuous energy and jump by thermal activity. The structure, dielectric capacitance and ferroelectric polarization of the composite films were further analyzed. Finally, the performance of the mesoscale cooling device is simulated, which shows a promising avenue to high efficient double cycling refrigeration. More importantly, the results are helpful to understand the cycling principle of electrocaloric cooling. [ABSTRACT FROM AUTHOR]

We report the impact of dysprosium (Dy, with y = 0.01, 0.02, 0.05 and 0.08) substitution in (Na0.5 Bi0.5)0.94 Ba0.06TiO3 (NBT-6BT) lead-free ceramics. The structural, vibrational dielectric, ferroelectric and electrocaloric (EC) properties of all samples were systematically investigated. X-ray diffraction analysis revealed the coexistence of tetragonal (P4mm) and rhombohedral (R3c) structural phases at low content of Dy (y = 0.01, 0.02 and 0.05). The structural changes with the introduction of Dy were confirmed by Raman spectroscopy at room temperature. The evolution of the Raman spectra with temperature was found to be strongly correlated with the dielectric measurements. Higher stability of the ferroelectric (FE) phase was obtained at room temperature for the compositions y = 0.01, 0.02 and 0.05, with optimum values for y = 0.02 as remanent polarization Pr = 32µC/cm2, as well as piezoelectric coefficients d33 = 137 pC/N, kp = 0.27 and kt = 0.16, whereas a higher content of Dy (y = 0.08) induced a remarkable decrease of the ferroelectric and piezoelectric properties. Using the direct EC measurement, the ceramic corresponding to y = 0.02 exhibited a significant EC response, where ΔT = 1.2 K under 5 kV/mm. The incorporation of Dy was found to enhance the EC responsivity coefficient ζ = iT/ΔE), with a best value of ζ = 0.24 K.mm/kV for y = 0.02. [ABSTRACT FROM AUTHOR]

Commercial ultrasonic baths employ piezoelectric ceramic to generate cavitation. These ceramics vibrate with large amplitudes and their physical characteristics may be changed decreasing of the performance due to the heating. We develop an experimental study to evaluate the changes in the Butterworth-Van Dyke equivalent electric circuit of a piezoelectric disk caused by the temperature at range from 30 °C to 90 °C, typical of the commercial ultrasonic baths. The results show that motional resistance is significantly modified increasing the mechanical loss. The evaluation of the temperature effects suggests that is not need to use electronic circuits in these systems as resonance tracking. [ABSTRACT FROM AUTHOR]

We report on the enhancemenent of electrocaloric effect in solution cast polymer nanocomposites based on Poly(vinylidene fluoride- co -trifluoroethylene) [P(VDF-TrFE) 55-45] with Ca and Sn co-substituted BaTiO 3 ceramic fillers (Ba 0. 94 Ca 0.06 Ti 0.925 Sn 0.075 O 3 , BCST). Saturated hysteresis loops and normal ferroelectric behaviour of the copolymer-based nanocomposites -as opposed to the relaxor ferroelectric nature of the terpolymer-based ones-allow the utilization of the indirect method to estimate the electrocaloric properties. Both the dielectric constant and electrocaloric temperature change (ΔT) increases as the particle content increases. Maximum adiabatic temperature change was obtained as 6.96 K under 900 kV/cm for the 10 vol % BCST containing polymer composite around the Curie temperature of the copolymer (70 °C). This relatively large electrocaloric strength is slightly lower than those obtained for terpolymer-based nanocomposites. [ABSTRACT FROM AUTHOR]

The electrocaloric (EC) effect cooling technique of environmentally friendly lead-free thin film materials driven by electric fields has recently gained tremendous attention due to the urgent demand for microelectronic and integrated circuit refrigeration devices. However, the widespread use of lead-free materials in EC devices is seriously hindered due to the small electrocaloric temperature change (ΔT) within a narrow operation temperature span (T span) near room temperature. Here, lead-free Ba 0.85 Ca 0.15 Zr 0.1 Ti 0.9-x Sn x O 3 (BCZT-xSn, 0 ≤ x ≤ 0.03) thin films were prepared on substrates (Pt/Ti/SiO 2 /Si) via a sol-gel route. The BCZT-0.02Sn thin film presents an excellent EC effect (ΔT = 32.74 K, ΔS = 37.18 J kg−1 K−1) and large EC strength (ΔT/ΔE = 0.033 K cm kV−1, ΔS/ΔE = 0.037 J cm K−1 kg−1 kV−1) over a wide T span (∼26 K) under 1000 kV cm−1 near room temperature. The giant ΔT is mainly attributed to the emergence of an intermediate O phase and the formation of a multiphase (R, O and T phases) coexistence structure at room temperature, while the diffuse phase transition behavior is responsible for the wide T span. Our study provides a new idea for developing environment-friendly EC materials with an excellent room-temperature ΔT over a broad operational temperature region. [ABSTRACT FROM AUTHOR]

In this paper, we studied some ferroelectric properties of archetypal oxide uniaxial ferroelectric single crystals of Pb5Ge3O11 modified by Ba ions. They include dielectric, DSC, ferroelectric polarization, and electrocaloric effect (ECE) measurements. The measurements show that increasing Ba doping considerably influences all the measured parameters, mainly by lowering the Curie temperature, gradually diffusing the phase transition, and decreasing values of polarization as well as the coercive field. The decrease in overall ECE is influenced by decreasing polarization. Compared with the pure PGO single crystals, this decrease is from 1.2 K to 0.2 K. However, the effect of diffusing the phase transition increases the range of its occurrence (up to 30 K), which might be beneficial in applications. [ABSTRACT FROM AUTHOR]

We prepared a dense AgNbO3 ceramic using a conventional solid-state reaction method. The phase structure, electrical properties and electrocaloric effect (ECE) were systematically investigated. Large negative and positive ECEs (−4.38 °C at 65 °C and 2.3 °C at 210 °C) under an external electric field of 180 kV·cm−1 were obtained in the eco-friendly AgNbO3 antiferroelectric (AFE) ceramic due to affluent phase transition and a high electric field. The large positive and negative ECEs originated from the phase transition between ferrielectric (FIE) phases (the orthorhombic space group (Pmc21) and AFE phases (Pbcm) tuned by an applied external field. Additionally, a probable mechanistic model was proposed to illustrate the generation of positive and negative ECEs. This study may provide guidelines for the design of high-efficiency solid-state cooling devices. [ABSTRACT FROM AUTHOR]

Broadband photodetection has shown a great promise for diverse applications, while the realization of plateau photoresponse from ultraviolet (UV) to near‐infrared (NIR) spectral region is very challenging. Herein, we exploit photoexcited pyroelectric effect in a chiral hybrid perovskite, (N, N‐dimethylcyclohexylammonium)PbBr3 (1), serving as a new pathway to drive broadband photoactivities. It is a room‐temperature pyroelectric with large polarization of ≈6.4 μC cm−2 and high pyroelectric figure‐of‐merits (FV=1.0×10−2 cm2 μC−1 and FD=7.1×10−5 Pa−1/2). Strikingly, light‐induced pyroelectric effect arising from spontaneous polarization is observed in 1, which cover UV (266 nm) to NIR‐II (1950 nm) full spectral region. The broadband photoresponses actualized by pyroelectricity break the limit of optical band gap. As the first demonstration of photo‐pyroelectricity covering UV‐to‐NIR spectral region in hybrid perovskites, this work paves a pathway to assemble high‐performance smart devices. [ABSTRACT FROM AUTHOR]

The refrigeration technology of electronic devices has faced severe challenges with the increasing demand for miniaturization and high frequency, and the research on the electrocaloric effect (ECE) of ferroelectric nanomaterials has made it possible to solve such problems. Due to the symmetry breaking on surfaces of a ferroelectric crystal, the polarizations on surfaces are different from those inside the crystal, which can significantly affect the electrocaloric properties of the materials. In addition, considering the electromechanical coupling between the spontaneous polarization and stress field, the applied stress has a drastic influence on the ECE of the material. In this paper, the extrapolation length is incorporated in the phase-field method based on the time-dependent Ginzburg–Landau equation to investigate the effects of different stress and surface polarization on the ECE of PbTiO3 (PTO) nanocylinders. The stress–adiabatic temperature change (ATC) curves with different extrapolation lengths are obtained through the simulations, which reveal the effect of extrapolation length and stress on the PTO nanocylinders. The results of this paper can provide theoretical guidance for the design of next-generation solid-state cooling devices. [ABSTRACT FROM AUTHOR]

Design of pyroelectric crystals decoupled from piezoelectricity is not only a topic of scientific curiosity but also demonstrates effects in principle that have the potential to be technologically advantageous. Here we report a new method for the design of such materials. Thus, the co‐doping of centrosymmetric crystals with tailor‐made guest molecules, as illustrated by the doping of α‐glycine with different amino acids (Threonine, Alanine and Serine). The polarization of those crystals displays two distinct contributions, one arising from the difference in dipole moments between guest and host and the other from the displacement of host molecules from their symmetry‐related positions. These contributions exhibit different temperature dependences and response to mechanical deformation. Thus, providing a proof of concept for the ability to design pyroelectric materials with reduced piezoelectric coefficient (d22) to a minimal value, below the resolution limit of the method (<0.005 pm/V). [ABSTRACT FROM AUTHOR]

Electrocaloric effect is the adiabatic temperature change in a dielectric material when an electric field is applied or removed, and it can be considered as an alternative refrigeration method. Materials with ferroelectric order exhibit large temperature variations in the vicinity of a phase transition, while antiferroelectrics and relaxors may exhibit a negative electrocaloric effect. In this study, the temperature variation in polarization was investigated for epitaxial ferroelectric thin film structures based on PbZrTiO3 materials in simple or complex multilayered structures. We propose the intriguing possibility of a giant negative electrocaloric effect (ΔT = −3.7 K at room temperature and ΔT = −5.5 K at 370 K) in a simple epitaxial Pb(ZrTi)O3 capacitor. Furthermore, it was shown that abnormal temperature variation in polarization is dependent on the non-FE component introduced in a multilayered structure. No significant variation in polarization with temperature was obtained for PZT/STON multilayered structures around room temperature. However, for PZT/BST or PZT/Nb2O5 multilayers, an abnormal temperature variation in polarization was revealed, which was similar to a simple PZT layer. The giant and negative ∆T values were attributed to internal fields and defects formed due to the large depolarization fields when the high polarization of the FE component was not fully compensated either by the electrodes or by the interface with an insulator layer. The presented results make Pb(ZrTi)O3-based structures promising for cooling applications operating near room temperature. [ABSTRACT FROM AUTHOR]

This paper describes two perovskite high entropy oxide (PHEO) compositions: Pb(Hf0.2Zr0.2Ti0.2Nb0.2Mn0.2)O3 (Mn PHEO) and Pb(Hf0.2Zr0.2Ti0.2Nb0.2Al0.2)O3 (Al PHEO). Powders are prepared by conventional solid state sintering by first pre‐reacting the B‐site oxides, then adding PbO. Phase pure Mn PHEO powder is obtained following calcination of the mixed powders at 750 °C for 240 min; however, secondary phases persisted in Al PHEO for heat treatments from 750 °C to 1200 °C. The Mn PHEO undergoes an entropy‐driven phase transformation. Thin films of these compounds are synthesized by pulsed laser deposition (PLD) on a lead zirconate titanate seed layer on Pt‐coated SiO2/Si. The dielectric response of the Mn PHEO films show some contribution from space charge polarizability; in contrast, the Al PHEO films show a slim ferroelectric hysteresis loop and relaxor‐like characteristics. The Al PHEO has a dielectric permittivity of ≈2000 with a loss tangent <0.05 from 100 Hz to 100 kHz; it has a dielectric maximum at 105 ± 0.5 °C and a Burns' temperature of 234 ± 0.5 °C. Indirect measurements based on the Maxwell‐relations yielded a maximum electrocaloric temperature change of 8.4 K at 180 °C under the applied electric field of 1186 kV cm−1. [ABSTRACT FROM AUTHOR]

Electrocaloric cooling based on ferroelectrics is an eco-friendly technology. BaTiO 3 (BT)-based ferroelectric ceramics possess a high electrocaloric effect, which is significantly affected by grain size. Herein, fine and large grains' contributions to electrocaloric and related properties in BT-based ceramics are revealed via tuning sintered dwelling time (t s) in discontinuous grain growth (DGG) process with fine and large grains coexistence. With increasing t s , grain size change can be divided into two stages. The main change is the large-grain size (>100–200 μm) and number in the beginning DGG stage, and the properties' evolutions are mainly contributed by large grain change. The bigger grain size of large and fine grains contributes to the higher electrocaloric property, sharper phase transition, ferroelectric polarization (change rate), and coercive field. In the subsequent stage, fine grains gradually grow up (∼4.0–5.0 μm) while large-grain size decreases slightly. Here the properties' evolutions are influenced by the competitive contributions between fine and large grains. Large grain contribution is mainly attributed to the domain size effect, and fine grain contribution should embrace the domain size effect and grain-boundary pinning effect. This work contributes to a broad understanding of fine/large grain contributions in the promising BT-based electrocaloric ceramics. • Fine/large grain contributions in BT-based electrocaloric ceramics are revealed by tuning dwelling time (t s) in DGG process. • Large grains become bigger in beginning t s. Fine grains grow up while large-grain size decreases in subsequent t s. • Bigger grains contribute to higher ferroelectric polarization (change rate) and electrocaloric properties. • Large grain contribution mainly results from the domain size effect. • Fine grain contribution embraces domain size effect and grain-boundary pinning effect. [ABSTRACT FROM AUTHOR]

Bi 0.5 Na 0.5 TiO 3 (BNT)-based relaxors are considered as potential candidates for pyroelectric applications due to their excellent pyroelectric performances. However, the excellent pyroelectric response in BNT-based relaxors is generally accompanied by a rapid decrease in the depolarization temperature T d , limiting the operation temperature. Herein, we find that the mixed non-ergodic and ergodic relaxor states (a kind of transition system) can promote polarization rotation and remain the reversibility of polarization transformation simultaneously, thereby improving pyroelectric performances and maintaining the T d. The Li+-doped BNKT-based relaxors which possess such a transition state exhibit excellent room temperature (RT) pyroelectric coefficients (1247 μCm−2K−1), and also, the T d can maintain at 69℃. This work provides a strategy for further insight into the enhanced pyroelectric response, which promotes the development of eco-friendly pyroelectric applications (such as infrared detection, temperature sensors, and pyroelectric energy harvesting). [ABSTRACT FROM AUTHOR]

Biomass-assisted photocatalytic water splitting for hydrogen (H 2) production has attracted widespread interest, which is important for the development of green H 2 energy and the high value-added utilization of biomass. Although photothermal utilization can improve solar energy conversion efficiency, the elevated temperature also enhances the likelihood of electron-hole collisions. Herein, magnetically propelled PVDF/Fe 3 O 4 @g-C 3 N 4 spiral micromotors were constructed to easily foster the synergistic coupling of piezoelectric and pyroelectric effects, which is beneficial to enhance the directional migration of photogenerated carriers at high temperatures. With both piezo- and pyroelectric effects, the biomass glucose involved H 2 production rate on PVDF/Fe 3 O 4 @g-C 3 N 4 spiral micromotors is 42.3 μmol/h, representing a significant increase of 31.9 times compared to water splitting without these effects, and the average apparent quantum yield at ordinary pressure can reach 12.6 %. Furthermore, photoluminescence and variable-temperature electrochemistry demonstrate that the piezo-pyroelectric coupling can accelerate the separation of carriers. Meanwhile, COMSOL simulations and KPFM tests show that the built-in electric field of the sample is enhanced under the piezo-pyroelectric effect. The spiral micromotors can easily realize the synergism of piezoelectric and pyroelectric effects, which provides an effective strategy to enhance the built-in electric field and thereby improve the performance of photocatalytic H 2 evolution involving biomass reforming. [Display omitted] • Construction of magnetic micromotors to achieve piezo-pyroelectric bifunction. • The synergism of piezo- and pyro- electric effect is helpful to biomass reforming. • The biomass involved photocatalytic H 2 production rate can reach 42.3 μmol/h. • The apparent quantum yield of photocatalysis at ordinary pressure is 12.6 %. [ABSTRACT FROM AUTHOR]

• High-entropy strategy are proposed to design excellent electrocaloric materials. • The diverse local polar state enhances the macroscopic polarization of PT- x HE. • Dynamics transition of polar nanoregions dominate the mechanism of ECE in PT- x HE. • Optimal Δ T of 1.38 K achieved in PT-0.725HE. • Optimal T span of 116 K achieved in PT-0.775HE. Electrocaloric effect (ECE) materials have garnered significant interest for their potential in creating more portable, compact cooling solutions and reducing greenhouse gas emissions. Enhancing both the temperature change Δ T and the temperature span T span of ECE materials remains a formidable challenge. The diverse and flexible local polarization in the high-entropy ferroelectric materials hold promise for addressing this issue. A series of high-entropy ferroelectric ceramics with composition (1- x)PbTiO 3 - x Pb(Mg 0.2 Zn 0.2 Nb 0.2 Ta 0.2 W 0.2)O 3 has been synthesized using a solid-state reaction. As x increases, the crystal structure transitions towards a cubic phase, and the freezing temperature T f decreases from 92 to 47 °C. There is a notable reduction in the coercive field, and the polarization reaches the maximum value of 32.07 μC/cm2 at x = 0.75. Utilizing the direct method, the samples with x = 0.725 and x = 0.75 achieve an optimal Δ T of 0.35 K and T span of 123 K at an electric field of 20 kV/cm, respectively. The Δ T and T span of the sample with x = 0.75 observed by the indirect method surpass 1 K and 100 K, respectively, at an electric field of 55 kV/cm. This study highlights the potential of employing a high-entropy approach to achieve superior ECE performance, paving the way for the development of advanced cooling technologies. [ABSTRACT FROM AUTHOR]

• High purity Pb-free BCST ceramic synthesized via conventional sintering at 1400 °C. • Temperature dependent Raman, ε, c p show transitions at r → 233 ± 5 K O → 254 ± 5 K T → 373 ± 5 K C. • (C p , ε) Vs. T show hysteresis near T R-O & T O-T and non-hysteretic nature at T C. • EC response at T C evaluated via indirect method to enhance material's efficacy. • Obtained high |∆T| =0.52 K, |∆T/∆E| =0.31 K.mm/kV at non-hysteretic T C. Structural, dielectric, and electrocaloric properties were investigated in Pb-free ceramic (Ba 0.88 Ca 0.12)(Ti 0. 94 Sn 0.06)O 3 (BCST), synthesized using solid-state sintering method. Rietveld refinement of room temperature XRD data revealed the existence of pure perovskite tetragonal (P4 mm) phase. Temperature-dependent XRD analyses confirmed a structural transition from tetragonal to cubic phase near 380 K. Temperature-dependent dielectric constant (ε r) and specific heat capacity (C p) confirmed the presence of thermal hysteresis in two phase transitions near 233 ± 10 K and 254 ± 10 K, and a non-hysteretic behavior at the Curie temperature (T C ∼373 ± 10 K). A comprehensive Raman study corroborated the existence of phase transitions. Electrocaloric properties were determined using indirect method utilizing the non-hysteretic nature across T C. 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 BaTiO 3 -based ceramics. [Display omitted] [ABSTRACT FROM AUTHOR]

Electrocaloric solid-state refrigeration is a primary candidate for the next-generation cooling method for microelectronic systems. However, the mechanisms of electrocaloric effect remain unclear due to the lack of direct correlation evidence, especially for novel negative electrocaloric (NEC) effect. In this work, we develop a high-accuracy direct measurement method for simultaneously measuring local electrocaloric and electrostrain responses under ambient conditions, providing the accompanying electrostrain evidence during electrocaloric effect. Combined with experiments, thermodynamic analyses and finite element simulations, it is found that the electrostrain is very large when NEC and large positive electrocaloric (PEC) responses occur, and NEC effect is caused by ferroelectric-ferroelectric phase transition, while large PEC response originates from paraelectric-ferroelectric phase transition. Results also indicate that NEC temperature change does not increase with electric field, and shows the maximum temperature change at phase transition critical electric field, different from PEC temperature change increasing with electric field. The developed method provides an alternative and sensitive pathway to investigating electrocaloric effect. [Display omitted] [ABSTRACT FROM AUTHOR]

Environmentally friendly and highly efficient solid-state refrigeration devices based on electrocaloric effect (ECE) are promising substitutes for traditional vapor compression refrigeration. Ferroelectric materials with large polarization usually possess a significant adiabatic temperature change (ATC) near their first-order phase transition point. However, the narrow range of ATC around the high transition temperature unfortunately hinders their application as ECE coolers. As domain transition has been demonstrated as a powerful tool for tailoring the location and value of ATC, the versatile polar topologies discovered in the PbTiO 3 /SrTiO 3 (PTO/STO) ferroelectric superlattice offer a fruitful playground for creating domain transition-induced ECE. In this study, phase field simulation is employed to investigate the topological domain transitions and accompaning ECE response in the PTO/STO superlattice. By precisely designing the gradient layer thickness of STO, we acheive large ECEs with a peak value of ∼6 K and a wide temperature span near room temperature under a moderate electric field of ∼39 MV/m. With the increase of temperature, continuous topological domain transitions are observed in the superlattice system, starting from vertical c domain and transiting to a / c domain, followed by the formation of vortex-antivortex pairs, and finally transforming to horizontal a domain, which results in the above-mentioned room temperature ECE. The value of the ATC and temperature range of the large ECE response can be successfully adjusted by changing the STO occupation ratio in the PTO/STO superlattice. Our study sheds considerable insight into the topological domain transitions and offers guidance in engineering ferroelectric superlattice to achieve large ECE near room temperature. [Display omitted] [ABSTRACT FROM AUTHOR]

Solar–energy–induced photothermal–pyroelectric synergy sensing platform provides a win-win route to harvest waste heat and convert energy. However, the increase of carrier collision probability from high temperature inevitably leads to the loss of quantum efficiency. Herein, a flexible photothermal-pyroelectric electrode platform with Schottky junction was successfully constructed for maximum utilization of carrier. Under solar-simulated irradiation, the electron-rich and electron-depletion region formed by the Bi 13 S 18 Br 2 -S/alloy rectifier interface in flexible polyvinylidene difluoride-hexafluoropropylene film can increase the accumulation of photogenerated electrons. Meanwhile, the surface bound charges released by dipole oscillation in photothermal-pyroelectric field are continuously supplemented by the emerged high concentration of photogenerated electrons from the Schottky junction, and this synergistic effect prolonged their lifetimes and significantly improves the photoelectric conversion efficiency. To reasonably realize the accurate quantification of the simulated target, the cleavage activity of the CRISPR–Cas system can be specifically restored with the assistance of a synergistic dual-activator, releasing silica as a padlock to produce a target concentration-dependent photoelectric signal. Besides, the temperature variation on the electrode interface was simulated, revealing the synergistic effect between Schottky junction and photothermal–pyroelectric field under photoexcitation. This work broadens a new perspective for upgrading photoelectron utilization and overall performance of flexible sensing platform. [Display omitted] • A Schottky junction nanorods photonic structure with wide-spectrum absorption has been designed. • The promotion process of the Schottky barrier on carrier separation in the photothermal-pyroelectric is investigated. • The synergy of Schottky junction and photothermal-pyroelectric effect achieves efficient energy conversion. • The sensing platform integrates flexibility, strong thermal stability and high portability. [ABSTRACT FROM AUTHOR]

A novel two-pronged hybrid water transformation energy harvester (WTEH) strategically integrated solar-thermal effects with pyroelectric effects for facilitating water transformation and its associated energy extraction has been demonstrated. [Display omitted] • A novel two-pronged solar-driven hybrid generator (S-HPHG) has been demonstrated. • This ensemble enables yielding power by renewable hydrovoltaic and pyroelectricity. • Such S-HPHG's dual-modal power can reach up to 64 μW/m2 and 7.4 mW/m2, respectively. • The hybrid design drives efficiently multiple household electronic devices on demand. Manipulation of water for power generation has garnered significant research interest as it is renewable, sustainable, and a spontaneous form of energy production. However, energy conversion efficiency has remained constrained, primarily attributed to the slow evaporation rates of water and limited energy recovery strategies. Herein, we demonstrate a two-pronged hybrid water transformation energy harvester that strategically integrates solar-thermal effects with pyroelectric effects to boost water transformation and its associated energy extraction. The core of our unique ensemble consists of two layers: the upper layer features a composite film comprising carbon black (CB) and polyvinylidene fluoride (PVDF) coated onto bamboo fibers (CB/PVDF@BFP), which realizes solar-thermal and hydrovoltaic effects owing to the excellent solar-thermal and electrical activities of CB while the bottom layer is PVDF film to simultaneously generate pyroelectricity. Notably, the optimized CB/PVDF@BFP achieves a maximal temperature of ∼78 ℃ and an open-circuit voltage (V OC) and a short-circuit current (I SC) of 0.33 V and 1.6 μA, respectively. Consequently, we achieved a maximal output power density of 64 μW/m2 under one sun (25 ℃), surpassing the output under dark conditions by ∼92 %, and exceeding most similar designs. Moreover, the CB/PVDF@BFP film exhibits a maximal oscillation of ∼0.5 ℃/s and an evaporation rate of 1.44 kg·m−2·h−1 under optimized conditions, owing to the strategic inclusion of hydrophilic BFP. Concurrently, our ensemble also generates a maximum V OC , I SC and output power density of pyroelectricity of ∼80 V, 0.4 μA, and 7.4 mW/m2 (∼25.9-fold higher than the dark state), which is > ∼3.9-time higher than the similar reports, respectively. As proof of concept, our hybrid design can successfully power various household electronic devices (such as LED lights, electronic watches etc.) by storing the harvested energy into capacitors, thus showcasing its potential for practical applications. Our ensemble not only demonstrates remarkable performance but also lays the foundation for innovative concepts in the development of emerging hybrid micro/nano-generators, offering an avenue for harnessing ubiquitous ambient energy. [ABSTRACT FROM AUTHOR]

• Room temperature electrocaloric effect. • Bi 0.5 Na 0.5 TiO 3 -BaTiO 3 -based lead-free ceramics. • Relaxor PVDF-TrFE-CFE terpolymer-based nanocomposites. • PMMA coating on ceramic nanoparticles. • Reducing Joule heat in electrocaloric effect. Recently, electrocaloric effect (ECE)-based cooling technology has attracted a great deal of research attention. With a relatively high energy conversion efficiency (∼70 %) and no generating greenhouse gases, ECE-based cooling technology is suitable for use in the next generation of solid-state cooling devices. In this investigation, the PMMA layer was coated on the surface of (Bi 0.5 Na 0.5)TiO 3 -6BaTiO 3 -1.5 %BiCoO 3 (BNBT-BCO) nanofillers to reduce the Joule heat of BNBT-BCO/terpolymer (P(VDF-TrFE-CFE)) nanocomposite. From the ECE measurement result, the adiabatic temperature change (ΔT) of the BNBT-BCO@P/T-15 nanocomposite film reached 10.33 °C under 90 MV/m, which is 25 % higher than that of the BNBT-BCO/T-15 nanocomposite film (no PMMA coating, ∼8.29 °C) under the same electric field. In addition, the ΔT of the BNBT-BCO@P/T-15 nanocomposite film reached 17.52 °C under 150 MV/m at room temperature. This value is approximately 60 % higher than that of the pristine terpolymer films (ΔT ∼ 10.84 °C) and 17.4 % higher than that of BNBT-BCO@P/T-20 nanocomposite film (ΔT ∼ 14.92 °C). This work creates a new approach to using the surface coating on ceramic nanoparticles to reduce the Joule heat of the nanocomposites and improving the adiabatic temperature change (ΔT) and efficiency of ECE devices. [ABSTRACT FROM AUTHOR]

The present work investigates the pyroelectric properties of 0.94Na 1/2 Bi 1/2 TiO 3 -0.06BaTiO 3 -0.02Zn-xLa (NBT-6BT-2Zn-xLa; x = 0, 0.25, 0.5 and 1 in mole %) and its use in methylene blue (MB) dye degradation in wastewater. La doping is used to enhance the pyroelectric properties of NBT-6BT-2Zn for energy harvesting and pyrocatalysis applications. The 0.25 mol % La-doped sample consists of a maximum pyroelectric coefficient of 3.8 × 10−4 C m−2 °C−1 and shows a 55% MB dye decomposition. The presence of • OH and O 2 • − is confirmed by scavengers and radical trapping experiments. The repeatability test ensures the reusability of the NBT-6BT-2Zn-0.25La as a pyrocatalyst for dye degradation. The bulk form of NBT-6BT-2Zn-0.25La is also investigated to overcome the limitations of powder recovery in dye degradation. • The increase in d 33 for La-doped NBT-6BT-2Zn can be linked to changes in its microstructure and polarizability. • The pyroelectric current, voltage, and coefficient must be monitored as they significantly influence dye degradation. • The enhanced degradation efficiency in La-doped NBT-6BT-2Zn is attributed to a higher pyroelectric coefficient than that of pure NBT-6BT-2Zn. • The present study uses powder and bulk forms of La-doped NBT-6BT-2Zn pyrocatalyst to degrade MB dye in wastewater. [ABSTRACT FROM AUTHOR]

This paper is concerned with direct energy conversion of waste heat into electrical energy by performing the Olsen cycle on lead nickel niobate zirconate titanate (PNNZT) pyroelectric ceramics undergoing a relaxor-ferroelectric phase transition. First, isothermal bipolar displacement vs. electric field hysteresis loops were measured for different temperatures and electric field spans. The Curie temperature varied between 150 °C and 240 °C as the electric field increased from zero up to 3 MV/m. The energy and power densities of the Olsen cycle on PNNZT were measured by cycling the specimens over a wide range of temperatures, electric fields, and frequencies. A maximum energy density of 1417 J/L/cycle was recorded with 200 μm thick PNNZT cycled at 0.033 Hz between temperatures 20 °C and 240 °C and electric fields 0.3 MV/m and 9.0 MV/m. To the best of our knowledge, this is the largest energy density ever obtained experimentally for any pyroelectric material. In addition, a maximum power density of 78 W/L was measured by cycling the material temperature between 20 °C and 220 °C and applying the electric field between 0.3 MV/m and 9.0 MV/m at 0.09 Hz. [ABSTRACT FROM AUTHOR]

The electrocaloric effect (ECE) in lead-free relaxor ferroelectrics has gained significant interest over the past decades. However, certain aspects of the ECE in relaxor ferroelectrics, such as Bi0.5Na0.5TiO3, remain poorly understood. In this work, we investigate the ECE by considering Bi0.5Na0.5TiO3-SrTiO3 (BNT-ST) as an example. The results show that, for BNT-0.25ST ceramics, the directly-measured ECE is optimal when the freezing temperature is tailored to be about room temperature. For this material, ΔT = 0.51 K under an electric field of 6 kV/mm and the ECE has excellent thermal stability (the instability η ≤ 20% in the range 30–120 °C). The addition of strontium increases the cubic-phase fraction, enhances the local random field, and changes the local structure, as clarified by in situ Raman spectroscopy and piezoelectric force morphology. In addition, we discuss in detail the correlation between the ECE and local structure. This work thus improves our understanding of the ECE in BNT-based materials for EC cooling technologies. [ABSTRACT FROM AUTHOR]

A device concept of an electrocaloric solid-state refrigeration is presented in this paper. The core component of the device is flexural mode composite actuators, each of which is comprised of an electrocaloric layer and an elastic substrate layer bonded together. The composite actuators have an electric field induced temperature change due to the electrocaloric effect and also have large electric field induced flexural deformation due to the converse piezoelectric effect, which enables the device to bend to contact with the heat source (or heat sink) for transferring heat. An analytical model is derived by considering multi-physical couplings for an edge-clamped circular composite device, which can accurately predict the temperature change of the device as compared with the indirect approach derived from the Maxwell relation. The model shows that the temperature change is a combinatorial result from the couplings of thermal, electric, and mechanical field in the device. Moreover, the model sheds light on exploring the optimization of the solid-state refrigeration device and indicates that different thickness ratios and radius ratios of the composite actuators have a large influence on the cooling performance of the refrigerator. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Pyroelectric current measurements on the orthorhombic GdMnO3 polycrystalline sample are done to explore the intrinsic and extrinsic contributions. The measurements reveal poling temperature dependent pyrocurrent peaks at 20, 50 and 108 K. The pyrocurrent at 20 K and at 108 K are attributed to ferroelectric transition induced by the incommensurate spiral magnetic ordering of Mn spins and the release of trapped charges from the localized states, respectively. A detailed analysis on the broad pyrocurrent signal at 50 K suggests that it could be attributed to the thermally stimulated depolarization current effect due to the relaxation of defect dipoles induced by negatively charged Mn3+ ions and excess holes localized at Mn4+ sites. Importantly, the effect of the electric field due to the defect dipoles on the ferroelectric state is highlighted. The temperature dependent dielectric measurements under the magnetic field brought out the correlation between pyroelectric and dielectric properties. The influence of poling temperature dependent extrinsic effects on pyrocurrent suggests the choice of poling temperature on the study of polarization and the resultant multiferroicity in a spin-driven ferroelectric rare earth manganite system. [ABSTRACT FROM AUTHOR]

The multilayer electrocaloric ceramics (MLEC) are promising candidates for environmentally friendly refrigeration, since it possesses large electrocaloric effect (ECE) at a relatively low applied voltage. In this work, factors that may influence the ECE of MLEC are investigated. Experimental results demonstrate that the ECE of MLEC is strongly related to its effective volume fraction, and the effective volume fraction of the MLEC can be tailored by changing the thickness of the MLEC protective layer. Measurements show up to a 33.3% improvement of adiabatic temperature change when the thickness of MLEC protective layers is decreased by 70.0%. Meanwhile, the relaxation and the temperature range of the MLEC is increased with the increase of frequency. The enhanced ECE response is obtained over a broad temperature range from 0 °C to 50 °C in MLEC. It is found that the ECE response of MLEC could be enhanced by thinning the protective layer, and this enhancement is induced by the increasing of the effective volume fraction which is caused by the protective layer thinning. As a result, this work provides an effective and feasible way to develop high-performance MLEC components. [ABSTRACT FROM AUTHOR]

Pure perovskite Ba0.90Ca0.10TiO3 ceramics, with a relative density of between 79 and 98% and grain sizes larger than 1 µm, were prepared by solid-state reaction. The dielectric and electrocaloric properties were investigated and discussed considering the density and grain size of the samples. Room temperature impedance measurements show good dielectric properties for all ceramics with relative permittivity between 800 and 1100 and losses of <5%. Polarization vs. E loops indicates regular variation with increasing sintering temperature (grain size and density), an increase in loop area, and remanent and saturation polarization (from Psat = 7.2 µC/cm2 to Psat = 16 µC/cm2). The largest electrocaloric effect was 1.67 K for ceramic with GS = 3 µm at 363 K and electrocaloric responsivity (ζ) was 0.56 K mm/kV. These values are larger than in the case of other similar materials; thus, Ba0.90Ca0.10TiO3 ceramics with a density larger than 90% and grain sizes of a few µms are suitable materials for electrocaloric devices. [ABSTRACT FROM AUTHOR]

Noble‐metal‐free catalytic nanoparticles hold the promise being abundant, low‐cost materials having a small environmental footprint and excellent performance, albeit inferior to that of noble metal counterparts. Several materials have a long‐standing history of success in photocatalysis, in particular titanium dioxide, and in recent years more complex oxides and added functionality have emerged with enhanced performance. We will discuss different approaches related to the use of non‐centrosymmetric and polar oxide nanoparticles and how the bulk photovoltaic effect, piezoelectricity, and pyroelectricity add to photocatalysis and tribocatalysis. We pay special attention to discriminate between the role of free versus that of bound charges within the catalyst, which is crucial to disentangle the different contributions to the catalytic reaction for the benefit of the overall enhanced catalytic performance in e.g. wastewater treatment and ultimately water‐splitting. [ABSTRACT FROM AUTHOR]

Superhydrophobic conductive materials have attracted much attention because of their wide applications in oil–water separation, electromagnetic shielding, and human motion detection. Herein, we adopt a facile method to prepare a superhydrophobic conductive fabric. In brief, the composite fabric is composed of a cheap and elastic textile base, an interface layer polydopamine (PDA), functional layer aligned carbon nanotubes (ACNTs) and Cu nanoparticles, and low surface energy materials such as polydimethylsiloxane (PDMS). In this method, we encapsulate Cu nanoparticles on the surface of ACNTs, which improves the electrical conductivity of the fabric. PDMS could not only protect the indicated Cu nanoparticles from oxidation but also endow the fabric with superhydrophobicity and thus corrosion resistance. The results show that the PDA/ACNTs/Cu/PDMS fabric can maintain good electrical conductivity and excellent chemical stability and mechanical durability even after bending (500 times), solution immersion, and water washing. Furthermore, the combination of superhydrophobicity and electrical conductivity endows the PDA/ACNTs/Cu/PDMS fabric with an excellent electrocaloric effect and deicing performance. More interestingly, the prepared fabric can also be used to monitor human movements. This superhydrophobic conductive fabric has potential application prospects as waterproof materials, wearable electronics, heaters, and in other fields. [ABSTRACT FROM AUTHOR]

The electrocaloric effect (ECE) of Tin Titanate (SnTiO3) has been investigated in the present manuscript. A phenomenological model has been adopted for predicting electric polarization variation with temperature to examine electrocaloric properties such as entropy change, heat capacity change and relative cooling power. The results indicate the potential of this ferroelectric compound to achieve the ECE near Curie temperature (TC). It is useful as prospective candidate for cooling system in a wide temperature interval. The maximum change in entropy near TC obtained by phenomenological model has been compared with the value procured by Tarnaoui et al. [1]. The results confirm that the phenomenological model is undoubtedly beneficial for the prediction of the electrocaloric effect of ferroelectric materials. [ABSTRACT FROM AUTHOR]

To investigate the caloric effects in the CsH2PO4 ferroelectric, a modified pseudospin model of this crystal is used, which takes into account the dependence of the parameters of interaction between pseudospins on lattice strains. The model also takes into account the dependence of the effective dipole moment of a pseudospin on the order parameter. In the two-particle cluster approximation, the influence of the longitudinal electric field and hydrostatic pressure on the molar entropy of the crystal was studied. The electrocaloric and barocaloric effects were studied. The calculated electrocaloric temperature change is about 1 K; it can change its sign under the influence of hydrostatic pressure. Barocaloric temperature change is about -0.5 K; lattice anharmonicities were not taken into account in its calculations. [ABSTRACT FROM AUTHOR]