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.

Vibration induced refrigeration using ferroelectric materials.

This article aims to propose a cantilever based cooling device employing non-axis symmetric placement of bulk ferroelectric patches. Ambient mechanical vibrations produce large stresses in cantilevers resulting in elastocaloric effect associated with ferroelectrics. Further, design allows cascading of several cantilevers to achieve large cooling response. A finite element analysis of the system was performed using material properties of bulk 0.50Ba(Zr0.2Ti0.8)O3-0.50(Ba0.7Ca0.3)TiO3. An individual element could produce a peak elastocaloric effect of 0.02 K (324 K); whereas the proposed system could achieve a temperature drop of 0.2 K within 50 seconds (10 elements, 1.5 Hz). Furthermore, net cooling can be further improved about ~2 K (using 10 cantilevers) for a starting temperature of 358 K. This study shows that elastocaloric effect in ferroelectric materials is capable of converting waste mechanical vibration into refrigeration effect which is not reported so far.

Elastocaloric Effect in Carbon Nanotubes and Graphene.

Carbon nanotubes are famous for their many extraordinary properties. We use a thermodynamical approach, experimental data from the literature, and atomistic simulations to reveal one more remarkable property of the carbon nanotubes that has so far been overlooked. Namely, we predict the existence of very large elastocaloric effect that can reach up to 30 K under moderate loads. Potentially even larger values could be achieved under extreme loads, putting carbon nanotubes in the forefront of caloric materials. Other remarkable features of the elastocaloric effect in carbon nanotubes include linearity of elastocaloric temperature change in applied force (compressive or stretching), very weak dependence on the temperature, and an absence of hysteresis. Such features are extremely desirable for practical applications in cooling devices. Moreover, a similarly large elastocaloric effect is predicted for the graphene. The prediction of a large elastocaloric effect in carbon nanotubes and graphene sets forward an unconventional strategy of targeting materials with moderate caloric responses but the ability to withstand very large loads.

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.