Reversible and High-Temperature-Stabilized Strain in (Pb,La)(Zr,Sn,Ti)O3 Antiferroelectric Ceramics

Antiferroelectric (AFE) materials have a tremendous advantage as smart materials and large-strain actuators due to their unique reversible characteristic electric-field-induced strain (electrostrain) responses in comparison to piezoelectric effect and electrostriction. A key limitation to today's AFE actuators, however, is the poor temperature stability of electrostrain. In this work, a large reversible strain of 0.4% and an excellent thermal stability with a variation within ±5.5% from 20 to 190 °C were achieved for (Pb_0.97La_0.02)(Zr_0.85Sn_0.08Ti_0.07)O₃ (PLZST) AFE ceramics. A room-temperature electrostrain of 0.71% was obtained in virgin PLZST ceramics. It is intriguing to observe inconsistent strain curves between the first and further measured cycles, implying an incomplete reversible field-induced AFE-ferroelectric phase transition. A sharp electrostrain response in milliseconds was realized in the as-prepared PLZST ceramics. In addition, a phenomenological explanation was proposed to explain the extraordinary phenomena. Our results may shed light on the origin of the superior strain behaviors in AFE materials from the view of microscopic structure and macroscopic properties, and probably improve the understanding of the AFE phase transition.

Lead-Free Bilayer Thick Films with Giant Electrocaloric Effect near Room Temperature

Electrocaloric refrigeration utilizing ferroelectrics has recently gained tremendous attention because of the urgent demand for solid-state cooling devices. However, the low room-temperature electrocaloric effect and narrow operation temperature window hinder the implementation of lead-free ferroelectrics in high-efficiency cooling applications. In this work, chemical engineering and thick-film architecture design strategies were integrated into a BaTiO₃-based system to resolve this challenge. Novel environmental-friendly Ba(Zr_0.20Ti_0.80)O₃-Ba(Sn_0.11Ti_0.89)O₃ (BZT-BST) bilayer films of ∼13 μm in single-layer thickness were prepared by the tape casting process. A giant adiabatic temperature change, Δ T ∼ 5.2 K, and a large isothermal entropy change, Δ S ∼ 6.9 J kg^-1 K^-1, were simultaneously achieved at room temperature based on the direct measurements, which are much higher than those reported previously in many lead-free ferroelectrics. Moreover, the BZT-BST thick films exhibited a remarkably widened operation temperature range from about 10 to 60 °C. These outstanding properties were mainly attributed to the multiphase coexistence near room temperature, relaxor ferroelectric characteristics, and improved electric-field endurance of the bilayer thick films. This work provides a guideline for the development of environment-friendly electronic materials with both ultrahigh and stable electrocaloric performance and will broaden the application areas of lead-free ferroelectrics.

Pyroelectric Energy Conversion and Its Applications-Flexible Energy Harvesters and Sensors

Among the various forms of natural energies, heat is the most prevalent and least harvested energy. Scavenging and detecting stray thermal energy for conversion into electrical energy can provide a cost-effective and reliable energy source for modern electrical appliances and sensor applications. Along with this, flexible devices have attracted considerable attention in scientific and industrial communities as wearable and implantable harvesters in addition to traditional thermal sensor applications. This review mainly discusses thermal energy conversion through pyroelectric phenomena in various lead-free as well as lead-based ceramics and polymers for flexible pyroelectric energy harvesting and sensor applications. The corresponding thermodynamic heat cycles and figures of merit of the pyroelectric materials for energy harvesting and heat sensing applications are also briefly discussed. Moreover, this study provides guidance on designing pyroelectric materials for flexible pyroelectric and hybrid energy harvesting.

Energy Harvesting Research: The Road from Single Source to Multisource

Energy harvesting technology may be considered an ultimate solution to replace batteries and provide a long-term power supply for wireless sensor networks. Looking back into its research history, individual energy harvesters for the conversion of single energy sources into electricity are developed first, followed by hybrid counterparts designed for use with multiple energy sources. Very recently, the concept of a truly multisource energy harvester built from only a single piece of material as the energy conversion component is proposed. This review, from the aspect of materials and device configurations, explains in detail a wide scope to give an overview of energy harvesting research. It covers single-source devices including solar, thermal, kinetic and other types of energy harvesters, hybrid energy harvesting configurations for both single and multiple energy sources and single material, and multisource energy harvesters. It also includes the energy conversion principles of photovoltaic, electromagnetic, piezoelectric, triboelectric, electrostatic, electrostrictive, thermoelectric, pyroelectric, magnetostrictive, and dielectric devices. This is one of the most comprehensive reviews conducted to date, focusing on the entire energy harvesting research scene and providing a guide to seeking deeper and more specific research references and resources from every corner of the scientific community.

Giant Negative Electrocaloric Effect in (Pb,La)(Zr,Sn,Ti)O3 Antiferroelectrics Near Room Temperature

(Pb_0.97La_0.02)(Zr _xSn_{0.94- x}Ti_0.06)O₃ (PLZST) antiferroelectric ceramics with x = 0.75-0.90 have been fabricated and found to be a novel electrocaloric material system with a giant negative electrocaloric effect (Δ T = -11.5 K) and a large electrocaloric strength (|Δ T/Δ E| = 0.105 K cm kV^-1) near room temperature. Additionally, the PLZST antiferroelectric ceramic also exhibits a large positive electrocaloric effect around the Curie temperature. The giant negative effect and the coexistence of both positive and negative electrocaloric effects in one material indicate a promising possibility to develop mid- to large-scale solid-state cooling devices with high efficiency.

Electro-caloric effect in a BCZT single crystal

The electro-caloric effect of the [001]-oriented (Ba,Ca)(Zr,Ti)O₃ (BCZT) single crystal was investigated in a wide temperature range from −100 °C to Curie temperature (122 °C).

Polarization rotation and the electrocaloric effect in barium titanate

We study the electrocaloric effect in the classic ferroelectric BaTiO₃ through a series of phase transitions driven by applied electric field and temperature. We find both negative and positive electrocaloric effects, with the negative electrocaloric effect, where temperature decreases with applied field, in monoclinic phases. Macroscopic polarization rotation is evident through the monoclinic and orthorhombic phases under applied field, and is responsible for the negative electrocaloric effect.