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The concept of multisource energy harvesting has attracted attention in order to harvest multiple types of energy in a single material. In this work, Pb‐free (Ba,Ca)(Zr,Ti)O3 (BCZT) ceramics were used to investigate a combination of piezoelectric and pyroelectric energy harvesting behavior. The temperature dependence of the permittivity and the pyroelectric coefficient was measured, and the pyroelectric properties of BCZT were expected to improve near its orthorhombic–tetragonal phase transition temperature TO–T (∼40°C). The output voltage and current were measured using a BCZT plate, where the BCZT was oscillated under a temperature gradient to apply mechanical stress and temperature fluctuation simultaneously. The measured output voltage from the combined piezo‐ and pyroelectric contributions at a frequency of 2 Hz and with a load resistance of 10 MΩ was 1.4 times higher than the sole piezoelectric output voltage. The resulting combined output voltage was confirmed by finite element simulation. [ABSTRACT FROM AUTHOR]

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

Temperature stability of electrocaloric effect (ECE) is a thorny problem in ferroelectrics (FE). A general method is to design ferroelectric-to-relaxor phase transition at a sacrifice of electrocaloric (EC) strength. The Pb(Yb1/2Nb1/2)O3 antiferroelectrics (AFE) + Pb(Mg1/3Nb2/3)O3 relaxors strategy designed in this work is effective to tackle this dilemma [(1 -- x)PYN--xPMN, x = 0.08-0.36]. PMN addition induces a successive phase transition and dual phase boundaries of ferrielectric (FIE)-nonergodic relaxor (NER) and NER-ergodic relaxor (ER), where ferroelectric polarization/strain and ECE reach a localmaximum. Thermally stable ΔT is unexpectedly achieved in FIE (x = 0.14) and NER (x = 0.24), except for a generality for ER state (x = 0.30). A dome-like variation trend is observed in x = 0.14 and 0.24 with a wide temperature span of ~60 and ~55 K (±15%ΔTmax). Notably, x = 0.24 NER possesses a large directlymeasured ΔTmax ~0.64 K simultaneously. Dielectric/ferroelectric properties clarify that two-stage transition of AFE rigid-order de-texture and dissociation of de-textured AFE domains into polar nano-entities accounts for thermal stability of ΔT as the alternation of ordered antipolar domains to disorder relaxors serves as a buffer to compensate for the thermal-shock enhanced random field. This work not only accounts for the underlying mechanism for thermal stability of ΔT at FIE and NER side for the first time in physics but also provides an exotic approach to seek for high-performance EC materials in practical applications. [ABSTRACT FROM AUTHOR]

In this work, the evolution behavior of electrocaloric effect in BaTiO3‐based ceramics with different phase structures and phase transitions was compared. A paradigmatic system of (Ba0.85Ca0.15)(Ti1−xHfx)O3 ceramics was selected. Diffuseness exponent γ increases linearly with rising x. Electrocaloric temperature change (ΔT) shows an opposite variation, whereas temperature span (Tspan) displays the same tendency with γ changing. The degeneration of maximum polarization and polarization change rate contributes to the decrease in ΔT due to the diffusion phase transition, whereas the diffusion can lead to a large Tspan. The ceramic with a single ferroelectric or paraelectric phase shows a small ΔT but a high variation rate with elevating electric field (E), whereas a small variation rate is present in the phase‐transition region that shows a high ΔT. Besides, small electrocaloric strength (ΔT/ΔE) is obtained in the single‐phase region and increases with elevating E. A high ΔT/ΔE is present in the phase‐transition region but decreases with elevating E. When phase transition becomes diffusion, ΔT variation with E becomes obvious, whereas ΔT/ΔE dependence will decrease. These phenomena result from the difficult polarization orientation in single ferroelectric phase or weak polarization in paraelectric phase, and the easy polarization orientation in the phase‐transition region. [ABSTRACT FROM AUTHOR]

In this paper, we theoretically and experimentally reported a lead‐free pyroelectric infrared (PIR) detector using (Bi1/2Na1/2TiO3)‐BaTiO3(BNT‐BT) ferroelectric ceramics as the sensitive material. The variation of noise density, voltage response rate (RV), and specific detection rate (D*) with the modulation frequency under the current mode amplification circuit was investigated, and it was found that the lead‐free PIR detector showed high RV in the low frequency band. The RV and D* reached 1.51 × 105 V/W and 2.02 × 108 cmHz1/2W−1 at 10 Hz, respectively. The results were much superior to the PIR based on traditional commercial pyroelectric ceramics, indicating that BNT‐BT lead‐free ceramics have great potential in application to PIR detectors. [ABSTRACT FROM AUTHOR]

To investigate the effect of A‐site substitution on phase‐structure evolution and electrocaloric effect (ECE) in filled tungsten bronze ceramics, Sr2–3x/2LaxNaNb4.3Ta0.7O15 (x = 0, 0.02, 0.04, and 0.06) ceramics are prepared through a two‐step solid‐state reaction method. Rietveld refinement shows that La2O3 addition achieves a partial transition from orthorhombic (Im2a) to tetragonal phase (P4bm). A decrease in phase transition temperature, enhancement in distortion degree, and relaxation behavior are observed with increasing La2O3 content, as demonstrated by dielectric, in situ Raman spectra, and ferroelectric properties. The indirectly measured ECE shows a non‐monotonic variation, with room‐temperature ECE ranging from 0.19, 0.15, 0.23 to finally 0.19 K for x = 0, 0.02, 0.04, and 0.06 compositions, respectively. This evolution trend is explained by an interplay of relaxation and multiphase coexistence. Directly measured ECE is also performed and a positive ECE character with a good temperature stability is observed. This work not only establishes relationships between phase‐structure evolution and ECE in filled Sr2NaNb4.3Ta0.7O15 tungsten bronze ceramics, but also presents its possibility in applications of thermally stable EC devices. [ABSTRACT FROM AUTHOR]

The origin of the excellent properties of KTN‐based materials around Curie temperature (TC), which should be originated form the motion of polar nanoregions (PNRs), has attracted considerable research interest. In this paper, the relaxation of a KTa0.63Nb0.37O3 single crystal is discussed with the temperature dependence of permittivity. Moreover, its pyroelectric effect above TC is investigated. In detail, the pyroelectric coefficient decreases from ∼110.0 to ∼13.0 μC/(m2 K), with the temperature increasing from 22 to 33°C, and finally reduces to 0 at 100°C with PNRs disappear. Moreover, the dynamic dielectric nonlinearity for the KTN single crystal is studied in the paraelectric phase. To investigate these mechanisms, the amplitude and phase angle of the first and third harmonics under various electric fields, frequencies, and temperatures are analyzed. As a result, the motions of PNRs induced by electric field, which is pinned and depinned by the defect, are presented to explain the nonlinear dielectric response observed in the paraelectric KTN single crystal. [ABSTRACT FROM AUTHOR]

Although glass–ceramics have been widely explored for their thermal stability and mechanical properties, they also offer unique symmetry‐dependent properties such as piezoelectricity and pyroelectricity through controlled crystallization of a polar phase. This work examines crystallization of LiNbO3 in a 35SiO2–30Nb2O5–35Li2O mol% composition and crystallization of LiNbO3 and NaNbO3 in a 35SiO2–30Nb2O5–25Li2O–10Na2O mol% composition. Crystallization kinetics are examined using the Johnson–Mehl–Avrami–Kolmogorov (JMAK) theory where the Avrami exponent, n, is calculated to be 1.0–1.5. Microscopical analysis shows dendritic morphology, which when combined with the JMAK analysis, suggests diffusion‐controlled one‐dimensional growth. Adding Na2O to the glass composition increases the inter‐diffusivity of ions which causes LiNbO3 to crystallize faster and lowers the activation energy of transformation from 1054 ± 217 kJ/mol in the ternary composition to 882 ± 212 kJ/mol. Time‐temperature‐transformation diagrams are presented which show that the temperature for maximum rate of transformation for LiNbO3 is ∼650°C and for NaNbO3 is ∼715°C. [ABSTRACT FROM AUTHOR]

Recently, ferroelectric and antiferroelectric ceramic materials have gained a lot of interest for the development of environment-friendly highly-efficient electrocaloric refrigeration and energy-storage devices. In this work, lead-free Ba1−xLixTiO3 ceramics with x = 0, 0.01, 0.02, 0.03, 0.04, and 0.05 were synthesized by the conventional solid-state reaction method, and the effect of Li doping on dielectric, leakage current, ferroelectric, electrocaloric, and energy storage properties of BaTiO3 ceramics was systematically investigated. The XRD and Raman studies confirmed that the structure of Ba1−xLixTiO3 remains tetragonal as for BaTiO3. The Li substitution shifted the phase transition (TC) of BaTiO3 slightly towards the lower temperature side. Significant drop in leakage current was observed with an addition of Li content. The maximum values of the electrocaloric effect (ΔT), electrocaloric responsivity, and coefficient of performance were found to be 1.44 K, 0.24 × 10−6 K m/V, and 5.75, respectively, for x = 0.04 at an applied field of 60 kV/cm near the Curie temperature. The maximal value of energy storage density was found to be 0.42 J/cm³ with an energy storage efficiency of 60% for x = 0.05. Our results suggested that lead-free Ba1−xLixTiO3 ceramic material is a promising candidate for potential applications in solid-state refrigeration technology and high-efficiency energy storage devices. [ABSTRACT FROM AUTHOR]

With growing demand for high‐sensitivity infrared detectors in industrial temperature monitoring and medical systems, high‐performance pyroelectric materials are vitally required. In this work, large pyroelectric performance is achieved in (1 − x)Pb0.99Nb0.02[(Zr0.57Sn0.43)0.937Ti0.063]0.98O3–xBaTiO3 (1 − x)PNZST–xBT ceramics by tuning the ferroelectric (FE)‐relaxor phase boundary near room temperature. The FE‐ and ergodic‐relaxor phase boundaries are engineered by breaking the long‐range antiferroelectric order with the introduction of BaTiO3. It is found that the ceramics with x = 0.15 exhibit a large pyroelectric coefficient of 11.3 × 10–4 C m–2 K–1 and figures of merit of Fi = 20.1 × 10–10 m V–1, Fv = 3.44 × 10–2 m2 C–1, and Fd = 3.87 × 10–5 Pa–1/2 around room temperature due to engineered phase boundary. Our results provide the potential technological application for ultrasensitive infrared detector and scientific insights into pyroelectric ceramic design. [ABSTRACT FROM AUTHOR]

With the urgent need to explore low‐cost, high‐efficiency solid‐state refrigeration technology, the electrocaloric effects of ferroelectric materials have attracted much attention in the past decades. With the development of modern computing technology, the phase‐field method is widely used to simulate the evolution of microstructure at mesoscale and predict the properties of different types of ferroelectric materials. In this article, we review the recent progress of electrocaloric effects from phenomenological Landau thermodynamics theory to phase‐field simulation by discussing the microcosmic composition, mesoscopic domain structures, macroscopic size/shape, and external stimulus of strain/stress. More importantly, in searching for new ferroelectric electrocaloric cooling materials, it is possible to find materials whose free energy barrier height changes rapidly with temperature, such materials have a faster change rate with polarization temperature in terms of ferroelectric macroscopic properties, from them could get superior electrocaloric effects. We compile a relatively comprehensive computational design on the high performance of electrocaloric effects in different types of ferroelectrics and offer a perspective on the computational design of electrocaloric refrigeration materials at the mesoscale microstructure level. [ABSTRACT FROM AUTHOR]

Innovative cooling technologies are recognized by many industries as a crucial part of their system design. A large electrocaloric effect (ECE) and extended working temperature are the key issues hindering the realization of electrocaloric refrigeration technology. In this work, large ECE (ΔT = 0.8–0.9°C @ 4 kV/mm) with an ultrawide temperature span from 30 to 120°C is noted for lead‐free (Na1/2Bi1/2)0.80Sr0.20(Zn1/3Nb2/3)xTi1‐xO3 ceramics. The excellent ECE performance can be ascribed to the evolution of polar nanoregions. Our work suggests that this material is promising for applications in solid‐state refrigeration systems with a broad range of operating temperatures. [ABSTRACT FROM AUTHOR]

Antiferroelectric (AFE) materials are of great interest owing to their scientific richness and their utility in high‐energy density capacitors. Here, the history of AFEs is reviewed, and the characteristics of antiferroelectricity and the phase transition of an AFE material are described. AFEs are energetically close to ferroelectric (FE) phases, and thus both the electric field strength and applied stress (pressure) influence the nature of the transition. With the comparable energetics between the AFE and FE phases, there can be a competition and frustration of these phases, and either incommensurate and/or a glassy (relaxor) structures may be observed. The phase transition in AFEs can also be influenced by the crystal/grain size, particularly at nanometric dimensions, and may be tuned through the formation of solid solutions. There have been extensive studies on the perovskite family of AFE materials, but many other crystal structures host AFE behavior, such as CuBiP2Se6. AFE applications include DC‐link capacitors for power electronics, defibrillator capacitors, pulse power devices, and electromechanical actuators. The paper concludes with a perspective on the future needs and opportunities with respect to discovery, science, and applications of AFE. [ABSTRACT FROM AUTHOR]

Ceramic‐based dielectric capacitor are highly suitable for pulsed power applications due to their high power density and excellent reliability. However, the ultrahigh applied electric field limit their applications in integrated electronic devices. In this work, (1−x){0.96(Bi0.5Na0.5)(Ti0.995Mn0.005)O3‐0.04BiAlO3}‐xNaNbO3 (BNT‐BA‐xNN, x = 0, 0.04, 0.08, 0.12, and 0.16) ternary ceramics were designed to achieve excellent energy storage properties. It was found that the introduction of NaNbO3 (NN) effectively increase the difference (ΔP) between Pmax and Pr, resulting in an obvious enhancement of the energy storage properties. High recoverable energy storage density, responsivity, and power density, that is, Wrec = 2.01 J/cm3, ξ = Wrec/E = 130.69 J/(kV⋅m2), and PD = 25.59 MW/cm3, accompanied with superior temperature stability were realized at x = 0.14 composition. In addition, the thermal stable dielectric properties of the sample can be prominently improved with increasing NN content. The temperature coefficient of capacitance (TCC) of x = 0.16 composition is lower than 15% over the temperature range from 49°C to 340°C, with a high dielectric permittivity of 1647 and a low dielectric loss (0.0107) at 150°C. All these features show that the BNT‐BA‐xNN ceramics are promising materials for energy storage application. [ABSTRACT FROM AUTHOR]

Domain wall motions mainly affect all kinds of properties of ferroelectric materials, such as piezoelectricity, dielectric response, and mechanical loss, and the extrinsic contributions associated with domain wall motions have always been an important issue. In this study, the reversible and irreversible extrinsic contributions to the dielectric properties of [011]C‐oriented 0.27Pb(In1/2Nb1/2)O3‐0.46Pb(Mg1/3Nb2/3)O3‐0.27PbTiO3:Mn single crystals have been extracted by the Rayleigh analysis. We found that in the unpoled samples, the extrinsic contributions of reversible and irreversible domain wall motions to dielectric properties significantly reduced, whereas after poling, only the irreversible extrinsic contribution decreased. The pinning effect in the 2R domain structure is much weaker than that in the 4R domain structure, leading to the low enhancement of Qm and a slight decrease in piezoelectricity caused by acceptor doping in 2R domain structure. This study explores the domain wall dynamics of acceptor‐doped single crystals and mainly guides on further performance optimization in PbTiO3‐based relaxor single crystals. [ABSTRACT FROM AUTHOR]

The crystal structures, pyroelectric properties, and thermal stability of [111]‐oriented 0.5 mol% Mn‐doped 0.36Pb(In1/2Nb1/2)O3‐0.36Pb(Mg1/3Nb2/3)O3‐0.28PbTiO3 (Mn‐0.36PIN‐0.36PMN‐0.28PT) ternary single crystal were investigated. The temperature dependence of the Raman spectra and dielectric properties revealed that the crystal exhibited a rhombohedral (R) structure at room temperature, and ferroelectric R → tetragonal (T) and ferroelectric T to paraelectric cubic (C) phase transitions at 130 and 175°C respectively. The single crystal had a high remnant polarization of Pr = 38 μC cm–2 and coercive field of EC = 12 kV cm–1 at room temperature and a frequency of f = 100 Hz. The values of Pr and EC decreased with increasing temperature, exhibiting anomalies near their phase‐transition temperatures, which coincided with changes in the Raman spectra and dielectric properties. Furthermore, at 25°C and f = 100 Hz, the single crystal had high pyroelectric coefficients of p = 8.7 × 10−4 C m−2 K−1, figures of merit for the current responsivity of Fi = 3.5 × 10−10 m V−1, the voltage responsivity of Fv = 0.08 m2 C−1, and the detectivity of Fd = 30.1 × 10−5 Pa−1/2. These values were weakly dependent on temperature below 120°C. In addition, the room‐temperature pyroelectric coefficients of the ternary single crystal maintain over 83% of the original value at thermal annealing temperatures below 120°C. These outstanding pyroelectric properties, together with high thermal stability, indicate that [111]‐oriented rhombohedral Mn‐0.36PIN‐0.36PMN‐0.28PT ternary single crystal is a new potential candidate for infrared detection applications. [ABSTRACT FROM AUTHOR]

The issue of how to achieve an electrocaloric effect (ECE) and pyroelectric effect in a material simultaneously remains to be a challenge for developing practical solid‐state cooling devices and RF‐detectors. Here, we structure a polymorphic phase transition (PPT) region by doping modification in KNN‐based ceramics, which are developed to achieve the ECE. The direct measured ECE and pyroelectric properties are investigated in lead‐free (1‐x)K0.5Na0.5NbO3‐xBi0.5Na0.5ZrO3 (KNN‐xBNZ) ceramics. The adiabatic temperature change (∆T) of 0.22 K at 100°C, 0.14 K at 70°C and 0.16 K at 30°C can be obtained under an electric field of 35 kV cm–1 for x = 0.03, 0.04 and 0.05, respectively. In addition, the temperature dependence of pyroelectric coefficient (p) is established for all compositions via the Byer‐Roundy method. A large p of 454.46 × 10–4 C m–2 K–1 is detected at Curie temperature (TC) in the ceramics with x = 0.03. Achieving electrocaloric effect and pyroelectric performance simultaneously may shed light and provide a feasible design scheme for developing practically useful electrocaloric and pyroelectric materials. [ABSTRACT FROM AUTHOR]

Thermally stimulated depolarization current in magnetoelectric antiferromagnet Co4Nb2O9 were investigated above Néel temperature, and five current peaks (denoted as P0 ~ P4 in the order of ascending temperature) were observed. These peaks are related to holes which can be trapped by cobalt vacancies, their surrounding medium (self‐trapped), internal, and surface barrier layers. In low‐temperature range, the holes are bound to cobalt vacancies. The polarization caused by bound holes yields P0 peak at 46 K. In middle‐temperature range, the holes are localized by the surrounding medium forming polarons. The hopping motions of the self‐trapped holes create P2 peak at ~120 K. The microdisplacements around their locating positions for the self‐trapped holes lead to P1 peak, whose peak temperature strongly depends on the poling temperature but lower than that of P2 peak. In high‐temperature range, the holes are trapped by internal and surface barrier layers giving rise to P3 peak at ~150 K and P4 peak at ~230 K, respectively. [ABSTRACT FROM AUTHOR]

Ba(Zr0.2Ti0.8)O3‐x(Ba0.7Ca0.3)TiO3 (BZT‐xBCT) is a promising lead‐free ferroelectric system. In this paper, we present two sets of free energy coefficients and carry out phenomenological modeling to study the phase transition and electrocaloric effect. The calculated phase diagram is in excellent quantitative agreement with experiments. Furthermore, we propose a new method based on effective internal electric field to simulate polarization in the macroscopic paraelectric state of ferroelectric relaxor. The computed composition and temperature‐dependent entropy and temperature change induced by electrocaloric effect are in good agreement with the measured data available for single crystal. [ABSTRACT FROM AUTHOR]

We firstly reported the electrocaloric properties in relaxor (1−x−y)NaNbO3–yBaTiO3–xCaZrO3 ceramics, and high electrocaloric effect (∆T ~0.451 K and∣∆T/∆E∣~0.282 Km/MV) can be realized in the ceramics (x = 0.04 and y = 0.10) under low temperature and low electric field. Relaxor behavior of NaNbO3 ceramics can be found by doping both BaTiO3 and CaZrO3. In addition, optimized piezoelectric effects (d33 ~235 pC/N and d33* ~230 pm/V) can be observed in the ceramics (x = 0.04 and y = 0.10) due to the involved morphotropic phase boundary (MPB). Excellent piezoelectric effect (ie, d33~330 pm/V at 41°C, and d33*~332 pm/V at 60°C) can be found because of the characteristics of MPB. Good temperature reliability of piezoelectric effect can be shown because of both MPB and relaxor behavior. We believe that the ceramics with high electrocaloric effect and good piezoelectric effect can be considered as one of the most promising lead‐free materials for piezoelectric devices. Significant MPB and relaxor behavior can be revealed in NaNbO3 ceramics with BaTiO3 and CaZrO3 modified. Sequentially, the giant electrocaloric effect (?T ~ 0.451 K) and high piezoelectric effect (d33 ~ 330 pm/V) as well as good temperature stability were realized in the ceramics benefit by the MPB and relaxor behavior. It can be believed that this result can partly promote the investigation of lead‐free cermics. [ABSTRACT FROM AUTHOR]

Ba(Zr0.2Ti0.8)O3‐x(Ba0.7Ca0.3)TiO3 (BZT‐xBCT) is a promising lead‐free ferroelectric system. In this paper, we present two sets of free energy coefficients and carry out phenomenological modeling to study the phase transition and electrocaloric effect. The calculated phase diagram is in excellent quantitative agreement with experiments. Furthermore, we propose a new method based on effective internal electric field to simulate polarization in the macroscopic paraelectric state of ferroelectric relaxor. The computed composition and temperature‐dependent entropy and temperature change induced by electrocaloric effect are in good agreement with the measured data available for single crystal. [ABSTRACT FROM AUTHOR]

Abstract: The crystal structure, electromechanical properties, and electrocaloric effect (ECE) in novel lead‐free (Bi0.5K0.5)TiO3‐La(Mg0.5Ti0.5)O3 ceramics were investigated. A morphotropic phase boundary (MPB) between the tetragonal and pseudocubic phase was found at x = 0.01‐0.02. In addition, the relaxor properties were enhanced with increasing the La(Mg0.5Ti0.5)O3 content. In situ high‐temperature X‐ray diffraction patterns and Raman spectra were characterized to elucidate the phase transition behavior. The enhanced ECE (ΔT = 1.19 K) and piezoelectric coefficient (d33 = 103 pC/N) were obtained for x = 0.01 at room temperature. Meanwhile, the temperature stability of the ECE was considered to be related to the high depolarization temperature and relaxor characteristics of the Bi0.5K0.5TiO3‐based ceramics. The above results suggest that the piezoelectric and ECE properties can be simultaneously enhanced by establishing an MPB. These results also demonstrate the great potential of the studied systems for solid‐state cooling applications and piezoelectric‐based devices. [ABSTRACT FROM AUTHOR]

Abstract: Lead‐free ferroelectric ceramics (1–x)(Ba0.7Ca0.3)TiO3–xBa(Zr0.2Ti0.8)O3 (BCTZ100x) with x = 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, and 0.80 were evaluated for their pyroelectric energy harvesting performance, using the Olsen cycle. As the composition ratio x increased, the crystal phase changed to tetragonal, orthorhombic, rhombohedral, and cubic; the phase boundaries crossed each other in the vicinity of BCTZ70. The crossover phase transition behavior between first‐order and diffuse phase transition changed to only the diffusion phase transition with increasing x. A pinching effect occurred because an increase in dielectric constant was also observed. Energy densities ND of 229 mJ/cm3 and 256 mJ/cm3 for BCTZ50 and BCTZ80 were obtained, respectively, in temperature of 30°C‐100°C and an electric field of 0‐30 kV/cm. These ND values are over two times higher than that of soft–Pb(Ti,Zr)O3 (PZT), which exhibits piezoelectric performance equivalent to BCTZ50 at room temperature. Compared with soft–PZT, BCTZ50 and BCTZ80 exhibited larger ND values owing to their lower Curie temperatures (TC ~ 50°C‐110°C). We conclude that low–TC ferroelectrics are useful for pyroelectric energy conversion based on the Olsen cycle even if they are unsuitable for piezoelectric applications at high temperatures. [ABSTRACT FROM AUTHOR]

Abstract: High pyroelectric performance and good thermal stability of pyroelectric materials are desirable for the application of infrared thermal detectors. In this work, enhanced pyroelectric properties were achieved in a new ternary (1−x)(0.98(Bi0.5Na0.5)(Ti0.995Mn0.005)O3–0.02BiAlO3)–xNaNbO3 (BNT–BA–xNN) lead‐free ceramics. The effect of NN addition on the microstructure, phase transition, ferroelectric, and pyroelectric properties of BNT–BA–xNN ceramics were investigated. It was found that the average grain size decreased as x increased to 0.03, whereas increased with further NN addition. The pyroelectric coefficient p at room temperature (RT) was significantly increased from 3.87 × 10−8Ccm−2K−1 at x = 0 to 8.45 × 10−8Ccm−2K−1 at x = 0.03. The figures of merit (FOMs), Fi, Fv and Fd, were also enhanced with addition of NN. Because of high p (7.48 × 10−8Ccm−2K−1) as well as relatively low dielectric permittivity (~370) and low dielectric loss (~0.011), the optimal FOMs at RT were obtained at x = 0.02 with Fi = 2.66 × 10−10 m/V, Fv = 8.07 × 10−2 m2/C, and Fd = 4.22 × 10−5 Pa−1/2, which are superior to other reported lead‐free ceramics. Furthermore, the compositions with x ≤ 0.03 exhibited excellent temperature stability in a wide temperature range from 20 to 80°C because of high depolarization temperature (≥110°C). Those results unveil the potential of BNT–BA–xNN ceramics for infrared detector applications. [ABSTRACT FROM AUTHOR]

Abstract: The validity of Mn element on 0.93(Bi0.5Na0.5)TiO3‐0.07Ba(Ti0.945Zr0.055)O3 ceramics (BNT‐BZT‐xMn) is certified by doping. On account of multiple effects introduced by Mn, the appropriate Mn content facilitates property improvement effectively. Compared with pure BNT‐BZT, d33 of the component x = 0.25 increases about 8% up to 187 pC/N and Qm of the component x = 1 increases about 84% up to 197. Thermally stimulated depolarization currents (TSDC) measurement reveals Mn additive is helpful to pyroelectric properties as well. The Mn‐doped component x = 0.125 exhibits better pyroelectric performance at room temperature. Corresponding pyroelectric coefficient and the figures of merit reach up to 0.061 μC/(cm2 °C), Fi=217 pm/V, Fν = 0.023 m2/C, and Fd = 12.6 μPa−1/2, respectively, even superior to lead‐based ceramics. Similar pyroelectric advantage is also observed in the component x = 0.5 near depolarization temperature Td. Mn doping has slight harmful influence on the ferroelectric‐to‐relaxor transition temperature TF−R, as well as Td, but hardly shows restriction on application. These results confirm Mn doping is an available strategy to improve BNT‐based ceramics. Therefore, Mn‐doped BNT‐BZT ceramics will be excellent candidates in area of high‐power piezoelectric application and pyroelectric detectors. [ABSTRACT FROM AUTHOR]

Abstract: Pyrocurrent and dielectric properties of magnetoelectric antiferromagnet Co4Nb2O9 have been investigated. The sample shows 2 thermally activated dielectric relaxations in the temperature range far above Néel temperature with the low‐ and high‐temperature ones being a dipolar and Maxwell‐Wagner relaxations, respectively. Two types of dipoles: relaxing dipoles and magnetic‐field‐induced dipoles were found in the sample. An internal electric field is formed due to the ordering of relaxing dipoles. Three current peaks were observed. The 2 higher temperature current peaks correspond to the dielectric relaxations. The lowest temperature current peak contains a positive tip and negative dip. The tip and dip are related to the depolarization of ferroelectricity induced by external and internal fields, respectively. [ABSTRACT FROM AUTHOR]

Abstract: Pyrocurrent and dielectric properties of magnetoelectric antiferromagnet Co4Nb2O9 have been investigated. The sample shows 2 thermally activated dielectric relaxations in the temperature range far above Néel temperature with the low‐ and high‐temperature ones being a dipolar and Maxwell‐Wagner relaxations, respectively. Two types of dipoles: relaxing dipoles and magnetic‐field‐induced dipoles were found in the sample. An internal electric field is formed due to the ordering of relaxing dipoles. Three current peaks were observed. The 2 higher temperature current peaks correspond to the dielectric relaxations. The lowest temperature current peak contains a positive tip and negative dip. The tip and dip are related to the depolarization of ferroelectricity induced by external and internal fields, respectively. [ABSTRACT FROM AUTHOR]

Abstract: Considering finite size effect, ferroelectric nanowires may show novel phenomena compared to ferroelectric thin film and bulk. Here we investigated the effect of width and surface compressive stress on electrocaloric cooling in ferroelectric nanowire by using thermodynamic calculations and phase‐field simulations. It was found that the isothermal entropy change and adiabatic temperature change in nanowire are 50% larger than that in thin film due to different mechanical boundary conditions of nanowire and thin film. The largest electrocaloric temperature changes were shown to increase significantly either with the decrease in nanowire width or the increase with the surface compressive stress. It was also revealed that the largest intrinsic entropy changes are almost the same for different nanowires with different widths and various stresses. The present study therefore contributes to the understanding of size effects of electrocaloric cooling and provides guidance for experiments to design high‐efficiency cooling devices using ferroelectric nanosystems. [ABSTRACT FROM AUTHOR]

Abstract: The pyroelectric properties of Mn‐doped Aurivillius ceramics with different pseudo‐perovskite layers were investigated. The pyroelectric coefficients for 0.2 wt% Mn‐doped two‐layer CaBi2Nb2O9 (CBN–Mn), three‐layer Bi4Ti2.85Nb0.15O12 (BTN–Mn), and four‐layer CaBi4Ti3.95Nb0.05O15 (CBTN–Mn) ferroelectric ceramics were found to be on the order of 26.0, 54.4, 84.4 μC/m2K at room temperature, respectively. These values were closely associated with the number of octahedral layers in the pseudo‐perovskite blocks. The high pyroelectric coefficient, together with low dielectric permittivity and loss (tan δ < 0.003), results in to high figures of merit for the current responsivity, voltage responsivity, and detectivity. The excellent pyroelectric properties and high Curie temperatures (TC > 660°C) make the Aurivillius ceramics potential candidates for pyroelectric devices over a broad temperature range. [ABSTRACT FROM AUTHOR]

In this paper, the influence of phase evolution on polarization change and electrocaloric response in lead-free (Ba0.9Ca0.1)(Ti1− x Zr x)O3 ceramics ( BCTZ) was systematically investigated. With increasing Zr/Ti ratio, the phase structure and phase transition behavior were greatly changed, resulting in various temperature and electric field dependence of electrocaloric responses. For x=0.05, a peak electrocaloric temperature change 1.64 K (at 130°C) and corresponding entropy change 1.78 J·kg−1·K−1 were obtained for 0-7 kV·mm−1 electric field. Negative electrocaloric temperature change in −0.1 K was obtained below Curie temperature ( Tc), which may be induced by the orthorhombic-tetragonal ferroelectric phase transition. With the increase in x, the peak value of the electrocaloric response decreased but much better temperature stability was observed. Simultaneously the negative electrocaloric response gradually disappeared with the disappearance of the low temperature ferroelectric-ferroelectric phase transition. For x=0.2, electrocaloric response showed good temperature stability ranging from room temperature to 130°C, attributing to the relaxor ferroelectric feature. [ABSTRACT FROM AUTHOR]

The temperature stability of the electrocaloric effect ( ECE) in relaxor ferroelectric Pb0.85La0.1(Zr0.65Ti0.35)O3 ( PLZT) prepared by the hot-press sintering method has been investigated. Compared to the PLZTs prepared via the conventional sintering process, the hot-pressed PLZTs exhibit larger ECE and superior temperature stability. The hot-pressed sample with an appropriate content of excess PbO presents a high Δ T of 2.4°C and Δ S of 2.3 J kg−1·K−1, both of which are 30% greater than those of the conventionally sintered samples measured at 100 kV·cm−1. More importantly, the hot-pressed specimens display great stable electrical properties, including the dielectric breakdown strength and electrical resistivity in the temperature range from 0°C to 100°C, whose ECE instability, especially, is only one-half that of the samples prepared by the conventional solid-state method. In addition, the ECE and its stability of the hot-pressed sample can be further enhanced by increasing the operating electric field to a relatively high level of 200 kV·cm−1. This work demonstrates hot-press sintering is an effective method to fabricate ferroelectric ceramics with high ECE as well as desirable temperature stability. [ABSTRACT FROM AUTHOR]

Electrocaloric device structures have been developed as multilayer ceramics ( MLCs) based on fundamental research carried out on PMN-8 PT bulk ceramics. Two different MLC structures were prepared with nine layers each and layer thicknesses of 86 μm and 39 μm. The influence of the device design on its properties has been characterized by microstructural, dielectric, ferroelectric, and direct electrocaloric measurement. For direct characterization two different methods, ie temperature reading (thermistor and thermocouple) and heat flow measurement (differential scanning calorimetry), were used. A comparison of results revealed a highly satisfactory agreement between the different methods. This study confirms that MLCs are promising candidates for implementation into energy-efficient electrocaloric cooling systems providing large refrigerant volume and high electrocaloric effect. Due to their micron-sized active layers, they allow for the application of high electric fields under low operation voltages. We measured a maximum electrocaloric temperature change of Δ T=2.67 K under application/withdrawal of an electric field of Δ E=16 kV mm−1, which corresponds to operation voltages below 1.5 kV. [ABSTRACT FROM AUTHOR]

PZT95/5 ferroelectric ceramics are widely utilized in pulsed power devices and the remanent polarization Pr of poled PZT95/5 can characterize the shock-driven energy density. However, this remanent polarization is difficult to be measured nondestructively. In this article, a series of pyroelectric tests of poled PZT95/5 ceramics were conducted near room temperature, from 25°C to 20°C. A linear relation between Pr and pyroelectric coefficient p was found, that is, Pr=1190.5( K)× p, which provides an effective way to nondestructively estimate the value of Pr of the poled PZT95/5 ceramics by measuring the pyroelectric coefficient p at room temperature. According to Devonshire's phenomenological theory, this result could be explained by a modified equation: [ABSTRACT FROM AUTHOR]

The electrocaloric effect (ECE) is investigated through indirect measurement in two lead-free [Bi1/2(Na,K)1/2]TiO3-based ceramics that were previously reported to display giant electro-strains. In the Nb-doped ceramic, denoted as BNKT-2.5Nb, a decent temperature change of Δ T=1.85 K and an electrocaloric responsivity of Δ T/Δ E=0.37 (10−6Km V−1) are found around room temperature (32°C). While in the Ta-doped ceramic, BNKT-1.5Ta, a wide operation temperature range ( Tspan ~55 K) is observed near room temperature. Additional electrical measurements, as well as transmission electron microscopy experiments, are performed to identify the mechanisms of the ECE in both ceramics. [ABSTRACT FROM AUTHOR]

In this paper, we report on studies of the electrocaloric ( EC) effect in lead-free (1− x)Ba(Zr0.2Ti0.8)O3- x(Ba0.7Ca0.3)TiO3 ceramics with compositions range between 0.32 ≤ x ≤ 0.45. The EC effect was measured directly using a modified differential scanning calorimeter. The maximum EC temperature change, ΔTdirect = 0.33 K under an electric field of 2 kV/mm, was observed for the composition with x = 0.32 at ~63°C. We found that the EC effect peaks not only around the Curie temperature but also at the transition between the ferroelectric phases with different symmetries. A strong discrepancy observed between the results of the direct measurements and indirect estimations points out that using Maxwell's equations is invalid for the thermodynamic nonequilibrium conditions that accompany only partial (incomplete) poling of ceramics. We also observe a nonlinearity of the EC effect above the Curie temperature and in the temperature range corresponding to the tetragonal ferroelectric phase. [ABSTRACT FROM AUTHOR]

(Pb0.97La0.02)(Zr xSn0.89− xTi0.11)O3 ( x = 0.60, 0.62, 0.64, 0.66, 0.68, 0.70, 0.72, and 0.74) ceramics with the compositions in tetragonal antiferroelectric (AFE) region, near the morphotropic phase boundary, were prepared by using the conventional solid-state reaction process. Their electric field-induced phase transitional behaviors, composition- and temperature-dependent dielectric, depolarization, and pyroelectric properties were investigated systematically. The AFE to ferroelectric phase switching field EA-F decreased with increasing x, while depolarization temperature Td increased with a linear relationship of Td = 842 x-483. Enhanced pyroelectric coefficient with a value of 12.1 μC/cm2/K was obtained at 88°C for the ceramics with x = 0.68, which was four times larger than the reported values. Composition-dependent pyroelectric response over 24°C-140°C was realized by changing x from 0.60 to 0.74. The results also suggested that the enhanced pyroelectric response near Td was accompanied by a release of large Pr, caused by an induced ferroelectric to AFE phase transition. [ABSTRACT FROM AUTHOR]

The pyroelectric properties of Nb(Mn)-doped and Nb/Mn co-doped CaBi4Ti4O15 ( CBT) bismuth layer-structured ferroelectric ceramics were investigated. It was found that Nb/Mn co-doping resulted in stronger enhancement of pyroelectric properties than that of single Nb or Mn doping. The mechanism of doping effect was explained by the distortion of the [ BO6] octahedra induced by the doped Nb and Mn cations occupying the B-site of the pseudoperovskite structure. A large pyroelectric coefficient of 84.4 μC/m2K was obtained at room temperature for Nb/Mn co-doped CBT ( CBTN-Mn) ceramics, higher than that of pure, Nb or Mn-doped counterparts, being on the order of 35.9, 58.2, 44.0 μC/m2K, respectively. The enhanced pyroelectric coefficient together with reduced dielectric constant (99) and dielectric loss (0.002) led to greater improvement of figures of merit ( FOMs), including FOMs for voltage responsivity ( Fv ~ 3.95 × 10−2 m2/C) and detectivity ( Fd ~ 2.44 × 10−5 Pa−1/2), in CBTN-Mn ceramics. Furthermore, the temperature variations of Fv and Fd were found to be 24% and 68%, respectively, over a broad temperature range from room temperature to 350°C, making CBTN-Mn ceramics potential candidate for high-temperature pyroelectric devices. [ABSTRACT FROM AUTHOR]

In this study, aligned porous lead zirconate titanate ( PZT) ceramics with high pyroelectric figures-of-merit were successfully manufactured by freeze casting using water-based suspensions. The introduction of aligned pores was demonstrated to have a strong influence on the resultant porous ceramics, in terms of mechanical, dielectric, and pyroelectric properties. As the level of porosity was increased, the relative permittivity decreased, whereas the Curie temperature and dielectric loss increased. The aligned porous structure exhibited improvement in the compressive strength ranging from 19 to 35 MPa, leading to easier handling, better processability and wider applications for such type of porous material. Both types of pyroelectric harvesting figures-of-merit ( FE and F′E) of the PZT ceramics with a porosity level of 25-45 vol% increased in all porous ceramics, for example, from 11.41 to 12.43 pJ/m3/K2 and 1.94 to 6.57 pm3/J, respectively, at 25°C, which were shown to be higher than the dense PZT counterpart. [ABSTRACT FROM AUTHOR]

The solid solutions of (1− x)PbSc0.5Ta0.5O3-( x)PbHfO3 (PSTH( x)) with pure perovskite structure were fabricated by hot-pressing sintering method. The structural, dielectric, and pyroelectric properties of the PSTH( x) ceramics were investigated. It was found that the long-range ordering decreased and the grain size increased with the increase of x. The maximum dielectric constant of 21 000 at 100 Hz and the highest pyroelectric coefficient of 615 × 10−8 C·(cm2·K)−1 were obtained for an x value of 0.15, where the PSTH( x) ceramic showed the largest lattice distortion. [ABSTRACT FROM AUTHOR]