Satyanarayan Patel

Anti-Ferroelectric Ceramics for High Energy Density Capacitors

With an ever increasing dependence on electrical energy for powering modern equipment and electronics, research is focused on the development of efficient methods for the generation, storage and distribution of electrical power. In this regard, the development of suitable dielectric based solid-state capacitors will play a key role in revolutionizing modern day electronic and electrical devices. Among the popular dielectric materials, anti-ferroelectrics (AFE) display evidence of being a strong contender for future ceramic capacitors. AFE materials possess low dielectric loss, low coercive field, low remnant polarization, high energy density, high material efficiency, and fast discharge rates; all of these characteristics makes AFE materials a lucrative research direction. However, despite the evident advantages, there have only been limited attempts to develop this area. This article attempts to provide a focus to this area by presenting a timely review on the topic, on the relevant scientific advancements that have been made with respect to utilization and development of anti-ferroelectric materials for electric energy storage applications. The article begins with a general introduction discussing the need for high energy density capacitors, the present solutions being used to address this problem, and a brief discussion of various advantages of anti-ferroelectric materials for high energy storage applications. This is followed by a general description of anti-ferroelectricity and important anti-ferroelectric materials. The remainder of the paper is divided into two subsections, the first of which presents various physical routes for enhancing the energy storage density while the latter section describes chemical routes for enhanced storage density. This is followed by conclusions and future prospects and challenges which need to be addressed in this particular field.

Mechanical confinement for improved energy storage density in BNT-BT-KNN lead-free ceramic capacitors

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 fo...

Elastocaloric effect in ferroelectric ceramics

Elastocaloric effect has been experimentally demonstrated in bulk (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 polycrystalline ferroelectric material. Predictions were made using Maxwells 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.

A technique for giant mechanical energy harvesting using ferroelectric/antiferroelectric materials

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...

BaTiO3-based piezoelectrics: Fundamentals, current status, and perspectives

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...

Multiple caloric effects in (Ba0.865Ca0.135Zr0.1089Ti0.8811Fe0.01)O3 ferroelectric ceramic

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 Maxwells 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).

Tuning of dielectric, pyroelectric and ferroelectric properties of 0.715Bi0.5Na0.5TiO3-0.065BaTiO3-0.22SrTiO3 ceramic by internal clamping

This study systematically investigates the phenomenon of internal clamping in ferroelectric materials through the formation of glass-ceramic composites. Lead-free 0.715Bi(0.5)Na(0.5)TiO(3)-0.065BaTiO(3)-0.22SrTiO(3) (BNT-BT-ST) bulk ferroelectric ceramic was selected for the course of investigation. 3BaO - 3TiO(2) - B2O3 (BTBO) glass was then incorporated systematically to create sintered samples containing 0%, 2%, 4% and 6% glass (by weight). Upon glass induction features like remnant polarization, saturation polarization, hysteresis losses and coercive field could be varied as a function of glass content. Such effects were observed to benefit derived applications like enhanced energy storage density similar to 174 k J/m(3) to similar to 203 k J/m(3) and pyroelectric coefficient 5.7x10(-4) Cm-2K-1 to 6.8x10(-4) Cm-2K-1 by incorporation of 4% glass. Additionally, BNT-BT-ST depolarization temperature decreased from 457K to 431K by addition of 4% glass content. Glass incorporation could systematically increases diffuse phase transition and relaxor behavior temperature range from 70 K to 81K and 20K to 34 K, respectively when 6% and 4% glass content is added which indicates addition of glass provides better temperature stability. The most promising feature was observed to be that of dielectric response tuning. It can be also used to control (to an extent) the dielectric behavior of the host ceramic. Dielectric permittivity and losses decreased from 1278 to 705 and 0.109 to 0.107 for 6% glass, at room temperature. However this reduction in dielectric constant and loss increases pyroelectric figures of merit (FOMs) for high voltage responsivity (F-v) high detectivity (F-d) and energy harvesting (F-e) from 0.018 to 0.037 m(2)C(-1), 5.89 to 8.85 mu Pa-1/2 and 28.71 to 61.55 Jm(-3)K(-2), respectively for 4% added ceramic-glass at room temperature. Such findings can have huge implications in the field of tailoring ferroelectric response for application specific requirements

Enhanced energy harvesting in commercial ferroelectric materials

Ferroelectric materials are used in a number of applications ranging from simple sensors and actuators to ferroelectric random access memories (FRAMs), transducers, health monitoring system and microelectronics. The multiphysical coupling ability possessed by these materials has been established to be useful for energy harvesting applications. However, conventional energy harvesting techniques employing ferroelectric materials possess low energy density. This has prevented the successful commercialization of ferroelectric based energy harvesting systems. In this context, the present study aims at proposing a novel approach for enhanced energy harvesting using commercially available ferroelectric materials. This technique was simulated to be used for two commercially available piezoelectric materials namely PKI-552 and APCI-840, soft and hard lead-zirconate-titanate (PZT) pervoskite ceramics, respectively. It was observed that a maximum energy density of 348 kJm−3cycle−1 can be obtained for cycle parameters of (0–1 ton compressive stress and 1–25 kV.cm−1 electric field) using APCI-840. The reported energy density is several hundred times larger than the maximum energy density reported in the literature for vibration harvesting systems.

Enhancing electrical energy storage density in anti-ferroelectric ceramics using ferroelastic domain switching

Capacitors form an indispensable part of many modern electrical and electronic devices. An ideal capacitor is expected to possess high power and energy density along with enhanced energy recovery characteristics. Anti-ferroelectric materials form a suitable candidate for ceramic-based capacitor applications, owing to their low loss and high energy density. However, these materials show ample room for improvement through physical means. In this regard, the present work deals with mechanical tuning of the energy storage density and recoverable efficiency in known anti-ferroelectric materials. For this study, various configurations of (Pb1?xLax)(Zr0.90Ti0.10)1?x/4O3 (PLZTx) ceramics have been investigated. Both mechanical confinement and temperature applications have been shown to improve the performance characteristics of all selected compositions. This behavior has been explained on the basis of competing ferroelectric and ferroelastic domain rotations. The application of suitable stress/temperature reduces hysteresis losses and delays anti-ferroelectric???ferroelectric phase transformation, which increases the electrical energy storage capacity of these materials. Mechanical confinement was observed to provide an increase in energy storage density and efficiency by approximately 38% and 25%, respectively, for the PLZT4 composition. The highest recoverable energy density of 698 m J cm?3 was achieved under compressive stress of a 100 MPa and 60 kV cm?1 applied electric field.

Elastocaloric and barocaloric effects in polyvinylidene di-fluoride-based polymers

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.