Perovskite lead-free dielectrics for energy storage applications

Materials exhibiting high energy/power density are currently needed to meet the growing demand of portable electronics, electric vehicles and large-scale energy storage devices. The highest energy densities are achieved for fuel cells, batteries, and supercapacitors, but conventional dielectric capacitors are receiving increased attention for pulsed power applications due to their high power density and their fast charge-discharge speed. The key to high energy density in dielectric capacitors is a large maximum but small remanent (zero in the case of linear dielectrics) polarization and a high electric breakdown strength. Polymer dielectric capacitors offer high power/energy density for applications at room temperature, but above 100 °C they are unreliable and suffer from dielectric breakdown. For high-temperature applications, therefore, dielectric ceramics are the only feasible alternative. Lead-based ceramics such as La-doped lead zirconate titanate exhibit good energy storage properties, but their toxicity raises concern over their use in consumer applications, where capacitors are exclusively lead free. Lead-free compositions with superior power density are thus required. In this paper, we introduce the fundamental principles of energy storage in dielectrics. We discuss key factors to improve energy storage properties such as the control of local structure, phase assemblage, dielectric layer thickness, microstructure, conductivity, and electrical homogeneity through the choice of base systems, dopants, and alloying additions, followed by a comprehensive review of the state-of-the-art. Finally, we comment on the future requirements for new materials in high power/energy density capacitor applications.

Electroceramics for High-Energy Density Capacitors: Current Status and Future Perspectives

The increasing demand for a whiter smile has resulted in an increased popularity for tooth whitening procedures. The most classic hydrogen peroxide-based whitening agents are effective, but can lead to enamel demineralization, gingival irritation, or cytotoxicity. Furthermore, these techniques are excessively time-consuming. Here, we report a nondestructive, harmless and convenient tooth whitening strategy based on a piezo-catalysis effect realized by replacement of abrasives traditionally used in toothpaste with piezoelectric particles. Degradation of organic dyes via piezo-catalysis of BaTiO3 (BTO) nanoparticles was performed under ultrasonic vibration to simulate daily tooth brushing. Teeth stained with black tea, blueberry juice, wine or a combination thereof can be notably whitened by the poled BTO turbid liquid after vibration for 3 h. A similar treatment using unpoled or cubic BTO show negligible tooth whitening effect. Furthermore, the BTO nanoparticle-based piezo-catalysis tooth whitening procedure exhibits remarkably less damage to both enamel and biological cells. Tooth whitening has attracted significant interest; however, most techniques are potentially destructive. Here, the authors model the replacement of standard abrasives in toothpaste with piezoelectric particles for catalytic degradation of organic stains and report less damage than hydrogen peroxide treatment.

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Piezo-catalysis for nondestructive tooth whitening.

Refrigeration is of vital importance for modern society—for example, for food storage and air conditioning—and 25 to 30 per cent of the world’s electricity is consumed for refrigeration1. Current refrigeration technology mostly involves the conventional vapour compression cycle, but the materials used in this technology are of growing environmental concern because of their large global warming potential2. As a promising alternative, refrigeration technologies based on solid-state caloric effects have been attracting attention in recent decades3–5. However, their application is restricted by the limited performance of current caloric materials, owing to small isothermal entropy changes and large driving magnetic fields. Here we report colossal barocaloric effects (CBCEs) (barocaloric effects are cooling effects of pressure-induced phase transitions) in a class of disordered solids called plastic crystals. The obtained entropy changes in a representative plastic crystal, neopentylglycol, are about 389 joules per kilogram per kelvin near room temperature. Pressure-dependent neutron scattering measurements reveal that CBCEs in plastic crystals can be attributed to the combination of extensive molecular orientational disorder, giant compressibility and highly anharmonic lattice dynamics of these materials. Our study establishes the microscopic mechanism of CBCEs in plastic crystals and paves the way to next-generation solid-state refrigeration technologies. Colossal barocaloric effects are observed in the plastic crystal neopentylglycol and found to originate from the extensive molecular orientational disorder, giant compressibility and highly anharmonic lattice dynamics of the material.

Colossal barocaloric effects in plastic crystals

A review of flexible perovskite oxide ferroelectric films and their application

Stress-induced and thermal-induced depolarization studies along with X-ray diffraction were performed on lead zirconate titanate ferroelectrics of different compositions, PbZr0.52Ti0.48O3 (PZT 52/48) and PbZr0.95Ti0.05O3 (PZT 95/5). Specimens were shock loaded perpendicular to the polarization vector. It was found that the polarity of the stress-induced charge released by PZT 52/48 and 95/5 was opposite to the polarity of the charge generated due to the piezoelectric effect. PZT 52/48 was only partially (45%) depolarized under 1.5 ± 0.1 GPa mechanical compression, as opposed to PZT 95/5 which was fully depolarized. The experimental results indicate that the stress-induced depolarization mechanisms are different for these two compositions. PZT 52/48 is transformed to a state with lower polarization, while PZT 95/5 undergoes a phase transition to a non-polar antiferroelectric phase.

Depolarization mechanisms of PbZr0.52Ti0.48O3 and PbZr0.95Ti0.05O3 poled ferroelectrics under high strain rate loading

A new type of energy storage devices utilizing multilayer Pb(Zr0.95 Ti0.05 )0.98 Nb0.02 O3 films is studied experimentally and numerically. To release the stored energy, the multilayer ferroelectric structures are subjected to adiabatic compression perpendicular to the polarization direction. Obtained results indicate that electrical interference between layers (10-120 layers) during stress wave transit through the structures has an effect on the generated current waveforms, but no impact on the released electric charge. The multilayer films undergo a pressure-induced phase transition to antiferroelectric phase at 1.7 GPa adiabatic compression and become completely depolarized, releasing surface screening charge with density equal to their remnant polarization. An energy density of 3 J cm-3 is successfully achieved with giant power density on the order of 2 MW cm-3 , which is four orders of magnitude higher than that of any other type of energy storage device. The outputs of multilayer structures can be precisely controlled by the parameters of the ferroelectric layer and the number of layers. Multilayer film modules with a volume of 0.7 cm3 are capable of producing 2.4 kA current, not achievable in electrochemical capacitors or batteries, which will greatly enhance the miniaturization and integration requirements for emerging high-power applications.

Multilayer PZT 95/5 Antiferroelectric Film Energy Storage Devices with Giant Power Density

Relaxor ferroelectric single crystals have triggered revolution in electromechanical systems due to their superior piezoelectric properties. Here the results are reported on experimental studies of energy harvested from (1-y-x)Pb(In1/2Nb1/2)O3–(y)Pb(Mg1/3Nb2/3)O3–(x)PbTiO3 (PIN-PMN-PT) crystals under high strain rate loading. Precise control of ferroelectric properties through composition, size and crystallographic orientation of domains made it possible to identify single crystals that release up to three times more electric charge density than that produced by PbZr0.52Ti0.48O3 (PZT 52/48) and PbZr0.95Ti0.05O3 (PZT 95/5) ferroelectric ceramics under identical loading conditions. The obtained results indicate that PIN-PMN-PT crystals became completely depolarized under 3.9 GPa compression. It was found that the energy density generated in the crystals during depolarization in the high voltage mode is four times higher than that for PZT 52/48 and 95/5. The obtained results promise new single crystal applications in ultrahigh-power transducers that are capable of producing hundreds kilovolt pulses and gigawatt-peak power microwave radiation.

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Ultrahigh energy density harvested from domain-engineered relaxor ferroelectric single crystals under high strain rate loading.

The development of relaxor ferroelectric single crystal technology is driven by the ability to tailor ferroelectric properties through domain engineering not achievable in polycrystalline materials. In this study, three types of domain-engineered rhombohedral Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 crystals were subjected to transverse high strain rate loading. The experimental results indicate that the domain configuration has a significant effect on the stress-induced depolarization and the associated charge released. A complete depolarization of the single-domain crystals with 3m symmetry is observed, while multidomain crystals with 4mm and mm2 symmetries retain a fraction of their initial remanent polarization. The complete depolarization of single-domain crystals is unique without transition to a non-polar phase, with a stress-induced charge density of 0.48 C/m2. This is up to three times higher than that of the multidomain crystals and PbZrxTi1−xO3 ferroelectric ceramics that are critical for ultrahigh-power transducer applications. The main offering of this work is to propose a detailed mechanism for complete stress-induced depolarization in ferroelectric crystals which does not involve an intermediate transformation to a non-polar phase.

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Complete stress-induced depolarization of relaxor ferroelectric crystals without transition through a non-polar phase

Systematic studies of the depolarization of Pb(Zr0.52 Ti0.48)O3 (PZT 52/48) poled piezoelectric ceramic samples were performed using thermal heating and explosive longitudinal-shock compression. The electric charge density that is released due to thermal heating at a rate of 0.9 K/min was consistent for all sample sizes (Q = 27.8 μC/cm2). The charge density that is released due to shock compression was practically equal to that released due to thermal heating. The PZT 52/48 samples were completely depolarized by longitudinal shock waves at shock front pressures of PSW = 1.5 ±0.2 GPa. The electric charge that the samples release can be transformed into pulsed power. Miniature explosive-driven ferroelectric generators containing PZT 52/48 ceramic elements with a volume of 0.35-3.5 cm3 are capable of converting the depolarization charge into pulses of high voltage with amplitudes of up to 22 kV and high power with a peak power of up to 0.35 MW within a time interval of 0.3-1.5 μs .

Vladimir G. Antipov

Papers

Depolarization mechanisms of PbZr0.52Ti0.48O3 and PbZr0.95Ti0.05O3 poled ferroelectrics under high strain rate loading

Multilayer PZT 95/5 Antiferroelectric Film Energy Storage Devices with Giant Power Density

Ultrahigh energy density harvested from domain-engineered relaxor ferroelectric single crystals under high strain rate loading.

Complete stress-induced depolarization of relaxor ferroelectric crystals without transition through a non-polar phase

PZT 52/48 Depolarization: Quasi-Static Thermal Heating Versus Longitudinal Explosive Shock