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This work deals with enhancing piezoelectric energy harvesting by incorporating different auxetic structures and varying geometrical parameters. A bimorph consisting of polyvinylidene fluoride as a piezoelectric layer and brass auxetic substrate (re-entrant, s-shape, and elliptical holes) are considered for analysis. A finite element method-based simulation is performed to find the best auxetic systems that provide higher power output. The environmental vibration is taken for energy harvesting; thus, the first resonance frequency is below 100 Hz. The maximum power of ∼0.52, ∼0.67, and ∼0.79 mW is estimated for piezoelectric energy harvesters (PEH’s) re-entrant, s-shape, and elliptical holes. The auxetic re-entrant, s-shape, and elliptical substrate-based PEHs show 200%, 300%, and 333% more power than the solid substrate (conventional design). However, the elliptical-based auxetic structure obtains a maximum power density of 0.004 66 mW/mm3. The stresses in all structures are within the permissible limit; hence, any design can be used for practical applications. All three auxetics have comparable geometrical dimensions and the same material is used; thus, auxetic behavior is independent of the material employed and depends on the structure’s shape. The estimated power is higher than that reported in the literature.

Ba0.9Ca0.1TiO3 (BCT) ceramic was prepared via a mixed-oxide route. Its microstructural characterization was done using x-ray diffraction, Raman spectrum, and scanning electron microscopy. Furthermore, its electrical properties were studied using dielectric measurement and impedance spectroscopy. BCT was also examined for the pyroelectric effect with the pyroelectric coefficient of ∼2.4 × 10−4 C/m2 K. An open circuit voltage was obtained during a temporal temperature change on BCT. Methylene blue dye degradation was recorded due to pyrocatalytic reactions in 120 heating/cooling cycles. The results show that pyrocatalysis could be an effective solution for the utilization of pyroelectric energy for water cleaning applications.

Ferroelectric solid-state refrigerators have the potential to develop as a competitive not-in-kind refrigeration technology. However, their functionality is limited to below Curie temperature for ferroelectricity to exist. This work reports the relatively unexplored strain gradient-induced caloric effect in ferroelectrics known as a flexocaloric effect (FCE). The FCE can manifest beyond the Curie temperature as entropy changes in a dielectric material are achieved employing strain-induced polarization, which, in turn, produces a caloric effect. This study reports FCE analysis of BaTi0.87Sn0.13O3 ceramics in a cantilever configuration. Different strain gradients were induced to produce the FCE by using the temperature-dependent polarization. A maximum temperature change of ∼1.4 K (310 K) was achieved using a strain gradient of 5000 m−1. The same material was also studied for the electrocaloric effect, which was observed to be 0.3 K (310 K). Results indicate that the FCE could be a potential alternative to electrocaloric refrigeration.

The present work demonstrates the effect of the grain size on electrocaloric and pyroelectric properties in BaTiO3-based ceramics prepared by a chemical coating method and then sintered in a reducing atmosphere at different temperatures. In a grain size of 136 ± 50 nm to 529 ± 245 nm, the electrocaloric temperature change increases from 0.30 K to 0.63 K under the electric field of 4 MV/m at the ferroelectric–paraelectric phase transition. The corresponding entropy change, heat extraction capacity, coefficient of performance, and electrocaloric strength exhibit a twofold increase (i.e., 0.31 J/kg K–0.75 J/kg K, 148 J/kg–303 J/kg, 7–14, and 0.0075 K cm/kV–0.016 K cm/kV, respectively). The effects of the grain size on the pyroelectric properties are established from the pyroelectric coefficient and the associated pyroelectric figures of merit (FOMs). The pyroelectric coefficient and pyroelectric FOMs exhibit about a fivefold increase with the increasing grain size. The pyroelectric energy harvesting is calculated for the Olsen cycle. The energy harvesting capabilities enhance from ∼96 kJ/m3 to ∼135 kJ/m3 when the cycle is operated at temperatures between 303 K and 423 K and an electric field between 1 MV/m and 4 MV/m. The results show that the increase in the grain size significantly improves the electrocaloric and pyroelectric properties. Furthermore, it is established that the pyroelectric properties are more sensitive to the grain size as compared to the electrocaloric effect when ceramics are prepared by the chemical coating-cum-sintering route. In summary, the present study suggests that microstructure control in BaTiO3 fabrication with the enhanced grain size can be an effective approach to enhance the pyroelectric and electrocaloric properties.

Mechanical confinement or restricted degrees of freedom have been explored for its potential to enhance the performance of ferroelectric devices. It presents an easy and reversible method to tune the response for specific applications. However, such studies have been mainly limited to uni- or bi-axial stress. This study investigates the effect of hydrostatic pressure on the ferroelectric behavior of bulk polycrystalline Pb0.99Nb0.02(Zr0.95Ti0.05)0.98O3. Polarization versus electric field hysteresis plots were generated as a function of hydrostatic pressure for a range of operating temperatures (298–398 K). The application of hydrostatic pressure was observed to induce anti-ferroelectric like double hysteresis loops. This in turn enhances the piezoelectric, energy storage, energy harvesting, and electrocaloric effects. The hydrostatic piezoelectric coefficient (dh) was increased from 50 pCN−1 (0 MPa) to ∼900 pC N−1 (265 MPa) and ∼3200 pCN−1 (330 MPa) at 298 K. Energy storage density was observed to improve...

We present a critical review that encompasses the fundamentals and state-of-the-art knowledge of barium titanate-based piezoelectrics. First, the essential crystallography, thermodynamic relations, and concepts necessary to understand piezoelectricity and ferroelectricity in barium titanate are discussed. Strategies to optimize piezoelectric properties through microstructure control and chemical modification are also introduced. Thereafter, we systematically review the synthesis, microstructure, and phase diagrams of barium titanate-based piezoelectrics and provide a detailed compilation of their functional and mechanical properties. The most salient materials treated include the (Ba,Ca)(Zr,Ti)O3, (Ba,Ca)(Sn,Ti)O3, and (Ba,Ca)(Hf,Ti)O3 solid solution systems. The technological relevance of barium titanate-based piezoelectrics is also discussed and some potential market indicators are outlined. Finally, perspectives on productive lines of future research and promising areas for the applications of these ma...

3BaO-3TiO2-B2O3 (BTBO) glass-added ferroelectric Ba0.85Sr0.15Zr0.1Ti0.9O3 (BST-BZT) ceramics were synthesized using a conventional solid state reaction route. BTBO glass settled at grain boundaries which has been confirmed from energy dispersive X-ray spectroscopy (EDX). Such effects were observed to benefit properties like the pyroelectric coefficient from 3.4 × 10−4 C/m2 K (0% glass) to 4.29 × 10−4 C/m2 K (2% by wt. glass) at 303 K. The dielectric constant decreased from 2937 to 2514 with 2% glass addition at 303 K (1 kHz). However, this reduction in dielectric constant increases the pyroelectric figure of merits (FOMs) for high current responsivity ( F i), voltage responsivity ( F v), detectivity ( F d), energy harvesting ( F e), and ( F e *) by 50%, 126%, 49%, 81%, and 76%, respectively, for 2% glass sample as compared with 0% glass at 303 K. Some of the FOMs even surpass the reported FOMs of well-known pyroelectric ceramics.

Inhomogeneous strain allows the manifestation of an unexplored component of stress-driven caloric effect (flexocaloric effect) and enhanced pyroelectric performance, obtainable significantly beyond the Curie point. A peak temperature change of 1.5 K (at 289 K) was predicted from first-principles-based simulations for Ba0.5Sr0.5TiO3 under the application of a strain gradient of 1.5 μm−1. Additionally, enhanced pyro-paraelectric coefficient (pyroelectric coefficient in paraelectric phase) and flexocaloric cooling 11 × 10−4 C m−2 K−1 and 1.02 K, respectively, could be obtained (at 330 K and 1.5 μm−1). A comparative analysis with prevailing literature indicates huge untapped potential and warrants further research.

Polyvinylidene di-fluoride-based polymers were investigated for elastocaloric and barocaloric effects. Bulk samples were subjected to uniaxial tensile and hydrostatic loading. Resulting strain profile (function of temperature) was used to predict the temperature change. A peak elastocaloric effect of 1.8 K was observed at 298 K (15 MPa). Alternately, a large barocaloric effect of ∼6 K was observed at 300 K (200 MPa). This was further improved to an astounding ∼19 K near 368 K (200 MPa). The results of this study are expected to greatly benefit the field of ferroelectric solid-state refrigeration and open another horizon for future exploration of multicaloric effects in ferroelectric polymers.

Multiple caloric effects have been investigated for Fe-doped bulk (Ba0.865Ca0.135Zr0.1089Ti0.8811Fe0.01)O3 (BCZTO-Fe) ferroelectric ceramic. Indirect predictions were made using Maxwell's relations in conjunction with data from experimental observations. It was revealed that bulk BCZTO-Fe has huge untapped potential for solid-state refrigeration. A peak electrocaloric effect of 0.45 K (347 K) was predicted for 0–3 kV.mm−1 electric field, significantly higher than other BCZTO based materials. A maximum elastocaloric cooling of 1.4 K (298 K) was achieved for applied stress of 0–200 MPa. Finally, an unforeseen component of electric field driven caloric effect has been reported as inverse piezocaloric effect, with a maximum temperature change of 0.28 K (298 K).

Elastocaloric effect has been experimentally demonstrated in bulk (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 polycrystalline ferroelectric material. Predictions were made using Maxwell's relationship for elastocaloric effect. A maximum elastocaloric effect of 1.55 K was observed for an initial material temperature of 340 K and applied compressive stress of 0–250 MPa (under a constant electric field of 2 MV m−1). The reported value is several times larger than the peak electrocaloric effect for the same material. The results indicate that ferroelectric materials possess a huge potential for elastocaloric refrigeration.

Ferroelectrics form an important class of materials and are employed for a variety of applications. However, specific applications dictate the need of tailored ferroelectric response. This creates a requirement to obtain ferroelectric materials with tunable properties. Generally, chemical modifications or domain engineering are employed to this effect. This study attempts to shed light on the use of compressive pre-stresses for tuning and enhancing the ferroelectric properties. For the purpose, polarization versus electric field hysteresis data for 68Pb(Mn1/3Nb2/3)O3-32PbTiO3 (PMN-PT) single crystals were obtained as a function of uniaxial compressive stresses and operating temperatures. These data were utilized to investigate the effects of mechanical confinement for four individual case studies of electrocaloric effect, electrical energy storage, pyroelectric, and piezoelectric effect. A significant improvement was obtained for all case studies. The adiabatic temperature change was improved by ≈80% (28 ...

With the advent of modern power electronics, embedded circuits and non-conventional energy harvesting, the need for high performance capacitors is bound to become indispensible. The current state-of-art employs ferroelectric ceramics and linear dielectrics for solid state capacitance. However, lead-free ferroelectric ceramics propose to offer significant improvement in the field of electrical energy storage owing to their high discharge efficiency and energy storage density. In this regards, the authors have investigated the effects of compressive stress as a means of improving the energy storage density of lead-free ferroelectric ceramics. The energy storage density of 0.91(Bi0.5Na0.5)TiO3-0.07BaTiO3-0.02(K0.5Na0.5)NbO3 ferroelectric bulk ceramic was analyzed as a function of varying levels of compressive stress and operational temperature .It was observed that a peak energy density of 387 mJ.cm-3 was obtained at 100 MPa applied stress (25oC). While a maximum energy density of 568 mJ.cm-3 was obtained for the same stress at 80oC. These values are indicative of a significant, 25% and 84%, improvement in the value of stored energy compared to an unloaded material. Additionally, material's discharge efficiency has also been discussed as a function of operational parameters. The observed phenomenon has been explained on the basis of field induced structural transition and competitive domain switching theory.

Ferroelectric materials are widely employed as piezoelectric materials for numerous energy harvesting systems. However, conventional systems employing direct piezoelectric effect for vibrational energy harvesting suffer from low energy density and high actuation frequency requirements. In this regards, the authors have presented a new technique for giant mechanical energy conversion using ferroelectric/antiferroelectric materials in a cyclic manner. The proposed method will allow for large electromechanical energy conversion in a wide frequency domain. The cycle was simulated for polycrystalline Pb0.99Nb0.02[(Zr0.57Sn0.43)0.94Ti0.06]0.98O3 (PNZST) antiferroelectric bulk ceramic. It was observed that for cycle parameters of (20 to 60 kV·cm−1 and 0 to 250 MPa), a harvesting energy density of 689 kJ·m−3·cycle−1 can be obtained for uniaxial compressive stress. While an energy density of 919 kJ·m−3·cycle−1 can be obtained for radial compressive stress with cycle parameters of (20 to 60 kV·cm−1 and 0 to 360 MPa). This is several orders of magnitude larger than the highest energy density reported in the literature.