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

Abstract

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(Zr0.20Ti0.80)­O3–Ba­(Sn0.11Ti0.89)­O3 (BZT-BST) bilayer films of ∼13 μm in single-layer thickness were prepared by the tape casting process. A giant adiabatic temperature change, ΔT ∼ 5.2 K, and a large isothermal entropy change, ΔS ∼ 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.

Electrocaloric Performance of Multilayer Ceramic Chips: Effect of Geometric Structure Induced Internal Stress

“…The configuration, together with the microstructure of the sintered MLCC samples, is presented in Figure , in which two MLCCs with different geometrical structures are compared as shown in Figure a. The sample with only one active layer has been reported to possess higher ECE performance. , However, the sample with this configuration bents after the sintering process in this work, and all of the samples show the shrinkage of the dielectric layers between electrodes is smaller than that of inactive layers. This could be attributed to the difference in sintering characteristics and thermal expansion coefficients between dielectric ceramic and electrode materials.…”

Electrostatic Actuating Double‐Unit Electrocaloric Cooling Device with High Efficiency

“…However, EC refrigeration devices based on ferroelectric ceramics are limited by the inherent brittleness of the materials. [ 11–13 ] It is necessary to use an external motor to drive solid parts or pump fluid media to achieve directional heat transfer, which reduces the COP of the device and increases the complexity of the cooling system. [ 14–17 ] Compared with the ferroelectric polymer poly(vinylidene fluoride‐trifluoroethylene) [P(VDF‐TrFE)], Curie temperature of the relaxor ferroelectric terpolymer poly(vinylidenefluorideter‐trifluoroethylene‐ter‐chlorofluoroethylene) [P(VDF‐TrFE‐CFE)] is near room temperature.…”

Designed Giant Room‐Temperature Electrocaloric Effects in Metal‐Free Organic Perovskite [MDABCO](NH4)I3 by Phase–Field Simulations

“…Method 1: The total entropy per mass (S) could be calculated from the partial derivative of thermodynamic energy density with respect to T. (17) The density ρ and heat capacity c p of MDABCO used in the work was 4039 kg m −3 and 1000 J kg −1 K −1 , respectively. [24] Supporting Information Supporting Information is available from the Wiley Online Library or from the author.…”

“…change (ΔT) in a polar material, which results from a change in its entropy (ΔS) due to the application or withdrawal of an external electric field under adiabatic conditions. Although a series of ferroelectric ceramics [9][10][11][12][13] and thin films [14][15][16][17] have been investigated, they still cannot satisfy the practical electrocaloric cooling application, especially at room temperature. Therefore, it is urgent to further regulate or explore ferroelectric materials to acquire giant room-temperature ECE.…”