Pyroelectric Figure Research Articles

Optimization of pyroelectric figure of merit of PNN-PZ-PT composition at morphotropic phase boundary

Ternary compounds are proven to be a more fascinating, owing to their potential to span a broader composition region of morphotropic phase boundary (MPB) – enhanced piezoelectric, electrostrictive, dielectric and ferroelectric properties. To activate defects dipoles, we perform MnO2 doping in ternary MPB compound 0.55Pb(Ni1/3Nb2/3)O3-0.135PbZrO3-0.315PbTiO3 [PNN-PZ-PT]. Temperature dependent dielectric spectroscopy reveals relaxor-ferroelectric nature of the synthesized ceramics. With the poling treatment, P-E loop of xMn-PNN-PZ-PT is softened, which emphasizes that the poling introduces higher order structural instability in MPB structure. The evolution of structural instability is as evidenced by the emergence of additional anomaly in thermal profile of dielectric constant due to electrical poling of xMn-PNN-PZ-PT and no systematic difference between polarizing behaviour of poled and unpoled specimen (Arrott plots). In association with defects dipoles, pyroelectric response based figure of merits (FOMs) of PNN-PZ-PT are improved. FOMs are characteristics of pyroelectric materials that insights about their suitability for specific application. Fi is suppressed with MnO2 doping and Fv, Fe and increases with MnO2 doping. Our study reveals that tailored and precise acceptor doping is crucial for the simultaneous optimization of all pyroelectric FOMs.

KNN composite ceramics with superior pyroelectric performance for self-powered thermal detector

The thermal detector based on pyroelectric effect has attracted widespread attention due to its self-powering and rapid response. Although phase boundary engineered lead-free potassium sodium niobate [K0.5Na0.5NbO3, KNN] based ferroelectrics exhibit promising for pyroelectric sensor application, the high dielectric constants (εr) of these materials significantly constrain their pyroelectric figures of merit (FOMs), owing to the inverse correlation between FOMs and εr. To address this problem, we innovatively introduce perovskite bismuth sodium titanate [Bi0.5Na0.5TiO3, BNT] with low εr and high pyroelectric coefficient as the second phase to construct a KNN/BNT composite. The introduction of BNT can not only remain the high pyroelectric coefficient (p=7.12 × 10−4 C m−2 K−1) of KNN matrix, but also result in superior FOMs (Fv increased by 74 %), outperforming previous KNN-based pyroelectric ceramics. The excellent pyroelectric performance originates from the unique composite microstructure with compositional heterogeneity. That is, both the low εr BNT enriched phase and refined grain size as well as the promoted vibration of Nb–O octahedron contribute to the superior pyroelectric performance. A self-powered thermal detector with great thermal response has been developed, which also exhibits potential for detecting ultraviolet energy and infrared radiation.

On-Demand MXene-Coupled Pyroelectricity for Advanced Breathing Sensors and IR Data Receivers.

MXene-inspired two-dimensional (2D) materials like Ti3C2Tx are widely known for their versatile properties, including surface plasmon, higher electrical conductivity, exceptional in-plane tensile strength, EMI shielding, and IR thermal properties. The MXene nanosheets coupled poly(vinylidene fluoride) (PVDF) nanofibers with d33 ∼-26 pm V-1 are able to capture the smaller thermal fluctuation due to a superior pyroelectric coefficient of ∼130 nC m-2 K-1 with an improved (∼7 times with respect to neat PVDF nanofibers) pyroelectric current figure of merit (FOMi). The significant enhancement of the pyroelectric response is attributed to the confinement effect of 2D MXene (Ti3C2Tx) nanosheets within PVDF nanofibers, as evidenced from polarized Fourier transform infrared (FTIR) spectroscopy and scanning probe microscopy (SPM). In subsequent studies, the practical applications of self-powered pyroelectric sensors of MXene-PVDF have been demonstrated. The fabricated flexible, hydrophobic pyroelectric sensor could be utilized as an excellent pyroelectric breathing sensor, a proximity sensor, and an IR data transmission receiver. Further, supervised machine learning algorithms are proposed to distinguish different types of breathing signals with ∼98% accuracy for healthcare monitoring purposes.

Research on indoor environmental monitoring technology and radiation intensity control method for industrial X-ray flaw detection

Abstract With the development of China’s economy, the application of industrial radiation flaw detection technology is becoming more and more widespread, and the radiation monitoring and protection of flaw detection work has become an important topic in the field of radiation safety and protection. This paper uses pyroelectric technology to track X-ray radiation levels in the environment. It also chooses the scale curve method for calibrating the pyroelectric dosimeter and figures out the scale factor at the same time. The neutron and photon dimensions are used to evaluate the personal dose equivalent. The applicable range of pyroelectric dosimeters is calculated and the method is applied for radiation dose monitoring in industrial X-ray flaw detection rooms. Concrete wall shielding is used to determine the design parameters of the flaw detection room and the location of the distribution points to improve the shielding capacity of the flaw detection room and control the radiation intensity. The monitoring value of the operation position of the flaw detection room of Leshan Leboiler Enterprises in 2018 was 258.2, which was 73 higher than that of 2019. The results of the on-site monitoring of the absorbed dose rate of the ambient air in the flaw detection room showed that the average absorbed rate ranged from 0.015 to 0.546 μSv/h, which was lower than the standard of 2.5 μSv/h, and the shielding capacity of the flaw detection room was better, and the intensity of the radiation could be effectively controlled.

Layered porous Na0.5Bi0.5TiO3-0.06BaTiO3 for enhanced pyroelectric thermal energy harvesting

Layered Na0.5Bi0.5TiO3-0.06BaTiO3 (NBT-6BT) ceramics of dense-porous-dense structure along the thickness are fabricated. The porous layer is sandwiched between the top and bottom dense layer, nullifying the electrode material's seepage into pores. Thus, porous pyroelectric material reduces the dielectric breakdown during poling and increases the repeatability of the poling process. The burnt-out polymer technique creates 10.7 %, 14.23 %, 21.3 % and 28 % porosity. The dielectric constant in layered porous structure decreased from 785 to 221 as the porosity increased from 5.4 % (pure NBT-6BT) to 28 % (layered NBT-6BT-12) at room temperature (poled condition). The introduction of porosity showed an increment of 124 % in the modified pyroelectric energy harvesting figure of merit Fe* for NBT-6BT-12 at 80 °C. The real-time thermal energy harvesting obtained by heating and cooling the pyroelectric material demonstrated equivalent voltage for NBT-6BT-12 layered porous structure. The layered porous structure can be a viable alternative for enhanced voltage sensitivity and energy harvesting.

Enhanced room-temperature electrocaloric and pyroelectric responses around morphotropic phase boundary and energy storage performance of lead-free Ba0.85Ca0.15Hf0.10Ti0.90O3 ceramics sintered at various temperatures

The electrocaloric (EC) cooling and energy storage capabilities of Pb-free ferroelectrics are thought to be a promising technology for developing environmentally friendly refrigeration and energy storage systems. The EC performance, energy storage and pyroelectric response of sol-gel derived Ba0.85Ca0.15Hf0.10Ti0.90O3 (BCHT) ferroelectrics sintered at various temperatures are investigated here. It is thoroughly explored how sintering temperature affects the structural and electrical characteristics of BCHT ceramics. According to structural analysis by X-ray diffraction, the morphotropic phase boundary (MPB) of tetragonal and orthorhombic phases is evolved in BCHT ceramics sintered at higher temperatures of 1250 and 1350 °C. The density, grain size, and dielectric constant of BCHT ceramics increase when the sintering temperature rises from 1150 to 1350 °C. The BCHT ceramic sintered at 1250 °C exhibits the highest room temperature pyroelectric coefficient p ∼ 15.21 10−4 C/m2K and the various pyroelectric figure of merits calculated are Fi = 7.46 10−10 m/V, Fv = 0.033 m2/C, FD = 31.82 10−6 Pa−1/2, Fe = 103.44 J/m3K2, and Fe* = 24.85 10−12 m3/J respectively. At the ambient temperature, BCHT ceramic sintered at 1250 °C with MPB displayed a high EC temperature change ΔT ∼ 0.56 K and EC efficiency ΔT/ΔE ∼ 0.28 Kmm/kV under relatively low field ΔE ∼ 20 kV/cm. The highest EC temperature change ΔT ∼ 1.01 K is also observed in BCHT ceramics sintered at 1250 °C with corresponding ΔT/ΔE ∼ 0.50 Kmm/kV at 87 °C. The observed values are higher than the value reported for other lead-free materials. The maximum recoverable energy density Jrec ∼ 116.18 10−3 J/cm3 and corresponding efficiency η ∼ 71.34 % has been observed in BCHT ceramics sintered at 1250 °C. These findings indicate that BCHT ceramics offer a promising way to develop high-performance pyroelectric sensors, electrocaloric refrigeration, and energy storage materials.

Combination of power generation and flexibility in piezo-pyroelectric hybrid nanogenerators by designing bimetal textured structure

Flexible piezo-pyroelectric hybrid nanogenerators (FPPNG) capable of harvesting body mechanical and thermal energy are considered as a desirable power supply for the next generation of wearable electronics. However, it’s difficult to simultaneously achieve high power generation capacity and flexibility. Here, a strategy to comprehensively enhance FPPNG by designing bimetal textured structure is proposed, where the Schottky junction BCZT:Ag particles and Cu nanorods are co-textured in the PDMS matrix. The quasi-connected fillers improve the interconnectivity while ensuring the flexibility of the material; besides, the introduced metal phases can enhance polarization. With this structure, both piezoelectric and pyroelectric figures of merit of the FPPNG increase by above 700% compared to the normal textured counterpart, while Young’s modulus can still keep a low value of 3.49 MPa. Furthermore, by recycling mechanical and thermal energy from running, the as-developed insole-shaped FPPNGs can efficiently charge the Bluetooth headset (from 20% to 30% by 0.5 h) and smart bracelet (from 3% to 20% by 1 h). This work provides a new paradigm for designing high-performance and flexible hybrid nanogenerators for self-powered electronics.

Quasi-harmonic approach to evaluate pyroelectric properties in Janus CrSeBr monolayer

Two-dimensional materials are emerging as promising dielectric materials and have enormous possibilities in wearable micro and nanoelectronics, sensor, and detectors. The theoretical calculation is performed to investigate the pyroelectric coefficient and pyroelectric figure of merit (FOM) of Janus CrSeBr monolayer. Quasi-harmonic approximation (QHA) is used to calculate primary (p1) and secondary (p2) pyroelectric coefficients. Spontaneous polarization is calculated for different temperatures using QHA. Pyroelectric coefficient (1.21 µC m−2 K at 300 K) is obtained for CrSeBr monolayer, which is times higher compared to MoSSe monolayer. A high FOM is found for CrSeBr monolayer m2 C−1), pm V−1). High FOM for voltage responsivity of CrSeBr monolayer could be beneficial for several commercial applications.

High pyroelectric response in Pb0.99Nb0.02[(Zr0.57Sn0.43)1−xTix]0.98O3 ceramics

AbstractBoth high pyroelectric coefficient and figure of merits of ferroelectric materials are desirable for infrared detection. In this work, we prepared Pb0.99Nb0.02[(Zr0.57Sn0.43)1−xTix]0.98O3 (0.060 ≤ x ≤ 0.080) ceramics, and the microstructure and electric properties were studied systematically. It is observed that the composition x = 0.07 shows enhanced pyroelectric properties around ambient temperature due to the ferroelectric–antiferroelectric phase transition, with the pyroelectric coefficient p = 6.83 × 10−4 C m−2 K−1 and the figures of merit Fi = 5.04 × 10−10 m V−1, Fv = 7.61 × 10−2 m2 C−1, and Fd = 3.46 × 10−5 Pa−1/2 at room temperature and the highest pyroelectric coefficient of 695.5 × 10−4 C m−2 K−1 and Fi = 1410.46 × 10−10 m V−1, Fv = 1587.39 × 10−2 m2 C−1, and Fd = 1182.94 × 10−5 Pa−1/2 at 36.7°C. These values are superior to other pyroelectric materials. These results indicate that this system is a promising pyroelectric material for the applications of infrared detectors.

Key role of tetragonality in the enhancement of ferroic response of modified Ba0.85Sr0.15Zr0.1Ti0.9O3

We examine the correlation of tetragonality factor and underlying ferroelectric response via performing B-site doping, more competent in comparison to A-site. B-site doping opens a route toward optimization of various physical parameters via promoting the off-centering of central ions. Here, we provide detailed investigation of the effect of doping in Ba0.85Sr0.15Zr0.1Ti0.9O3 (BSZT) modified with x wt. % CdO (x = 0, 1, 2) ceramics. Room temperature structural analysis emphasizes that tetragonality of the BSZT system increases with doping, which results in a realization of large spontaneous polarization and pinched PE loop by providing additional octahedral voids to move B-site cations. Additionally, Cd doping strengthens the anomaly in the Pyroelectric coefficient. This results in significant improvement in electrocaloric response and pyroelectric figure of merits. The electrocaloric response at ambient temperature enhances from 0.45 (x = 0%) to 0.69 J/Kg-K (x = 2%) ceramic. Cd doping improves energy storage efficiency and is found to be 61% (x = 0%) and 83% (x = 2%). A considerable change in the pyroelectric figure of merit is observed. Our study reveals that manipulation of tetragonality seems a suitable strategic route for developing effective pyroelectric and energy storage materials.

Comment on "Improper molecular ferroelectrics with simultaneous ultrahigh pyroelectricity and figures of merit" by Li et al.

Li et al. (Science Advances, 29 January, p. eabe3068) claim the discovery of two improper ferroelectrics, dabcoHClO4 and dabcoHBF4 (dabco = 1,4-diazabicyclo[2.2.2]octane), and that these materials exhibit superior pyroelectric figures of merit. This information is misleading because of the fundamental methodological errors and false conclusions, not to mention that these ferroelectrics were reported more than 20 years ago. They are proper ferroelectrics, for which the spontaneous polarization is the macroscopic order parameter. We show that the useful pyroelectric coefficients of dabcoHClO4 and dabcoHBF4 are about 1000 times lower than the coefficients reported by Li et al.

Microstructural tuning: A route towards realization of enhanced pyroelectric figure of merits of Sr and Zr doped barium titanate ceramics

In this article, we emphasize microstructural tuning approach to realize an enhanced pyroelectric energy conversion associated figure of merits (FOMs) in ferroelectric Ba0.85Sr0.15Zr0.1Ti0.9O3 (BSZT) ceramics. To develop porous microstructure in the ceramics, we employ BURPS (burning out of polymer sphere) technique using PMMA as a pore-forming agent. In present scenario, the porosity in the ceramics is intentionally being introduced for the noble cause of enhancement in pyroelectric figure of merits (Fe*, Fe,Fv). Here, we investigate the effect of porosity on structural, morphological, dielectric and ferroic characteristics and its correlation with pyroelectric property. We note that, in comparison to dense ceramic, the porous ceramics with 6.9% porosity level shows remarkable enhancement of 29% in Fe*, 24% in Fe, 53% in Fv at 303 K. The microstructural engineering in pyroelectric/ferroelectric ceramics opens the effective route towards the realization of high piezoelectric and pyroelectric figure of merits. Ferroic ceramics with good figure of merit are highly anticipated for their decisive role in the area of green energy harvesting, energy storage and infrared detection.

Enhanced Pyroelectric Coefficient in Ferroelectric Lead Zirconium Titanate Thick Films for Thermal Energy Harvesting Applications

Due to increase in growth population and energy demand, energy harvesting technology has become a sensational topic of research community. Amongst all the available energy harvesting technologies (mechanical, magnetic, wind, hydrothermal), harvesting waste heat has gained a lot of interest because of its cost effectiveness and availability of significant thermal fluctuations in industrial processes as well as in nearby surroundings. Therefore, efforts have been made on harvesting thermal energy through pyroelectric devices. Such devices have huge range of applications in fire alarms, heat sensors, infrared detectors, thermal imaging, gas analysis and so on. In the present study, the pyroelectric Lead Zirconium Titanate (PZT) thick films grown using modified sol-gel approach have been used for pyroelectric energy conversion. The effect of annealing temperature (450 °C, 450 °C and 650 °C) on the growth of PZT films has been monitored by investigating their dielectric, ferroelectric and pyroelectric properties. An appreciable enhancement in saturation and remnant polarizations from 17μC cm−2 to 24μC cm−2 and 13μC cm−2 to 22 μC cm−2 has been obtained when annealed temperature is increased from 550 °C to 650 °C respectively. A visible change in dielectric constant is also observed from 207 to 325 from dielectric constant–frequency curves with very small change in dielectric losses from 0.06 to 0.10 with increase in the annealing temperature from 550 °C to 650 °C at 1 MHz. The pyro electric coefficient and figure of merit are found to increase from 25 × 10−3 Cm−2K−1 to 230 × 10−3 Cm−2K−1 (p) and from 2.2 m2C−1 to 20 m2C−1 for the optimized PZT thick film based pyroelectric device with increase in the external DC bias field from 0.5 V to 2.5 V. The enhanced results of pyroelectric coefficient and figure of merit achieved in the present work are good indication of electrical energy harvesting through pyroelectricity.

Enhanced electrocaloric effect, energy storage density and pyroelectric response from a domain-engineered lead-free BaTi0.91Sn0.08Zr0.01O3 ferroelectric ceramic.

A BaTi0.91Sn0.08Zr0.01O3 (BTSZ) ceramic was prepared by a conventional solid-state reaction method. Its structural, dielectric, ferroelectric, and pyroelectric properties were carefully studied. The Rietveld refinement was used to characterize the structural proprieties of the synthesized ceramic. The microstructure was observed by scanning electron microscopy. Phase transitions observed in the temperature dependent dielectric permittivity (ε r-T and tan δ-T) showed a transition close to room temperature, resulting in improved piezoelectric, pyroelectric and electrocaloric performance. In addition, it was found that an electric field poling process changed the character of ε r-T and tan δ-T plots. Resonance modes in the polarized state, where maximum power transmission was achieved, were observed in the impedance spectrum. The extra-slim hysteresis loops revealed a relatively low coercive field and hysteresis loss related to the diffuse phase transition, which can significantly improve energy storage efficiency up to 75% at 100 °C. To characterize the electrocaloric effect (ECE), indirect and direct methods based on the thermodynamic approach were used. Both methods results showed good consistency and revealed a large ECE peak evolving along the phase diagram. Furthermore, pyroelectric figures of merit (FOMs) for voltage responsivity (F v), current responsivity (F i), energy harvesting (F E), new energy harvesting and detectivity (F d) were calculated. Finally, thermal energy harvesting (N D) was determined by using the Olsen cycle. The obtained maximum N D was 233.7 kJ m-3 when the Olsen cycle operated at 25-100 °C and 0-30 kV cm-1. This study introduces not only a technique to produce a high performance ceramic for refrigeration devices, but also broadens the range of applications for BT-based lead-free ferroelectrics beyond actuators, sensors, and energy harvesting to solid-state cooling.

Enhanced Pyroelectric Performance of Lead-Free Zn-Doped Na1/2Bi1/2TiO3-BaTiO3 Ceramics.

Lead-free Na1/2Bi1/2TiO3-BaTiO3 (NBT-BT) has gained revived interest due to its exceptionally good high power properties in comparison to commercial lead-based piezoelectrics. Recently, Zn-modified NBT-BT-based materials as solid solution and composites have been reported to exhibit enhanced depolarization temperatures and a high mechanical quality factor. In this work, the pyroelectric properties of Zn-doped NBT-6mole%BT and NBT-9mole%BT ceramics are investigated. The doped compositions of NBT-6BT and NBT-9BT feature a relatively stable pyroelectric property in a wide temperature range of ~37 K (300–330 K) and 80 K (300–380 K), respectively. A threefold increase in detector figure of merit is noted for 0.01 mole Zn-doped NBT-6mole% BT at room temperature in comparison to undoped NBT-6mole%BT and this increase is higher than those of major lead-free materials. A broad range of the temperature-independent behavior for the figures of merit was noted (303–380 K) for Zn-doped NBT-6mole% BT, which is 30 K higher than the undoped material. The large pyroelectric figures of merit and good temperature stability renders Zn-doped NBT-BT an ideal candidate for pyroelectric detector and energy harvesting applications.

A simple scheme for calculating the energy harvesting figures of merit of porous ceramics

Abstract We propose a scheme based on recursively applying analytical formulae for effective properties to a class of porous ceramics for calculating their energy harvesting figures of merit. We approximate the structure of freeze-cast PZT parallel laminae joined by links (or bridges) by a model that can be broken down into two directions along which the structure resembles a laminate. The effective coefficients obtained in the first step of the recursion are then used as input on the second step which gives the final effective moduli. The comparison of those with calculations via Finite Element Method (FEM) on a non-recursive model shows good agreement. Finally, we calculate the piezoelectric and pyroelectric figures of merit and compare them with experimental results. The proposed scheme is a good alternative since it relies only on known simple analytical formulae and has a very low computational cost with respect to other methods that may be applied to such a geometry.

Effect of surfactants on the growth and characterization of triglycine sulfate crystals

This study investigates the effect on crystal growth and physical properties of triglycine sulfate (TGS) single crystals grown in the presence of surfactants, namely the anionic surfactants sodium dodecyl sulfate (SDS) and sodium 1-decanesulfonate (S1-DS). Pure TGS as well as SDS_TGS and S1-DS_TGS single crystals have been grown from aqueous solution, using a temperature lowering technique. The use of surfactants affects both crystal growth rate and shape. Concerning the latter feature, SDS_TGS crystals show larger (010) faces (b-face) and the S1-DS_TGS crystals show an elongation in [010] direction (b-direction). All samples are monoclinic and show the same Curie temperature (49 °C) as pure TGS. The UV–Vis transmittance of the crystals is found to be decreased due to the presence of surfactants during the growth process. At room temperature, the relative permittivity of the samples is decreased from 10.5 for pure TGS to 7.5 and 5.5 for SDS_TGS and S1-DS_TGS crystals, respectively. However, all crystals show the same pyroelectric coefficient of 168 μC/(m2·K) at room temperature. With that, the pyroelectric voltage figure of merit (FOM) (pc/ (ε.ε0)) is increased from 201 kV/(m·K)for pure TGS up to 245 kV/(m·K) for SDS_TGS, and up to 317 kV/(m·K)for S1-DS_TGS. The energy harvesting figure of merit(pc2/ε·ε0) is increased from 30.37 J/(m3.K2) for pure TGS to 42.52 and 58 J/(m3.K2) for SDS_TGS and S1-DS_TGS crystals, respectively.

Enhanced pyroelectric response from domain-engineered lead-free (K0.5Bi0.5TiO3-BaTiO3)-Na0.5Bi0.5TiO3 ferroelectric ceramics

Enhanced pyroelectric response is achieved via domain engineering from [001] grain-oriented, tetragonal-phase, lead-free 0.2(2/3K0.5Bi0.5TiO3-1/3BaTiO3)-0.8Na0.5Bi0.5TiO3 (KBT-BT-NBT) ceramics prepared by a templated grain growth method. The [001] crystallographic orientation leads to large polarization in tetragonal symmetry; therefore, texturing along this direction is employed to enhance the pyroelectricity. X-ray diffraction analysis revealed a Lotgering factor (degree of texturing) of 93 % along the [001] crystallographic direction. The textured KBT-BT-NBT lead-free ceramics showed comparable pyroelectric figures of merit to those of lead-based ferroelectric materials at room temperature (RT). In addition to the enhanced pyroelectric response at RT, an enormous enhancement in the pyroelectric response (from 1750 to 90,900 μC m−2 K−1) was achieved at the depolarization temperature because of the sharp ferroelectric to antiferroelectric phase transition owing to coherent 180° domain switching. These results will motivate the development of a wide range of lead-free pyroelectric devices, such as thermal sensors and infra-red detectors.

Pyroelectric performance, dielectric response and conductive mechanism of BCHT lead-free piezoelectric ceramics via powder injection molding

Lead zirconate titanate (PZT) ceramics exhibit excellent piezoelectric performance, which expands piezoelectric applications scope. However, the usage of toxic PbO causes serious harm to humans and ecological environment. Lead-free environment friendly (Ba0.85Ca0.15)(Hf0.10Ti0.90)O3 (BCHT) ceramics exhibit enhanced electrical properties when prepared via the powder injection molding process, relating to the polymorphic ferroelectric phases coexistence. Excellent pyroelectric properties are obtained in the BCHT ceramics, where pyroelectric anomaly and peak appear around 45 °C and 95 °C in temperature dependent pyroelectric coefficient and figures of merit, respectively, which can be attributed to the polymorphic phase transition and ferroelectric phase transition. Abnormal drastic change and large peak values of pyroelectric properties around the Curie temperature TC make the BCHT ceramics promising application for critical temperature detection. The dielectric response contribution was analyzed by Rayleigh formula fitting, where the reversible contribution takes major role at low temperatures and the irreversible contribution takes main effect at high temperatures. The conduction activation energy is 0.71 eV for the BCHT ceramics, which correlates with the increased oxygen vacancies induced by cations evaporation during sintering.

Piezoelectric and pyroelectric effects induced by interface polar symmetry.

Interfaces in heterostructures have been a key point of interest in condensed-matter physics for decades owing to a plethora of distinctive phenomena-such as rectification1, the photovoltaic effect2, the quantum Hall effect3 and high-temperature superconductivity4-and their critical roles in present-day technical devices. However, the symmetry modulation at interfaces and the resultant effects have been largely overlooked. Here we show that a built-in electric field that originates from band bending at heterostructure interfaces induces polar symmetry therein that results in emergent functionalities, including piezoelectricity and pyroelectricity, even though the component materials are centrosymmetric. We study classic interfaces-namely, Schottky junctions-formed by noble metal and centrosymmetric semiconductors, including niobium-doped strontium titanium oxide crystals, niobium-doped titanium dioxide crystals, niobium-doped barium strontium titanium oxide ceramics, and silicon. The built-in electric field in the depletion region induces polar structures in the semiconductors and generates substantial piezoelectric and pyroelectric effects. In particular, the pyroelectric coefficient and figure of merit of the interface are over one order of magnitude larger than those of conventional bulk polar materials. Our study enriches the functionalities of heterostructure interfaces, offering a distinctive approach to realizing energy transduction beyond the conventional limitation imposed by intrinsic symmetry.