High electrocaloric effect in barium titanate-sodium niobate ceramics with core-shell grain assembly

Substantially Enhanced Electrocaloric Effect in Ba(Zr0.2Ti0.8)O3 Lead-Free Ferroelectric Ceramics via Lattice Stress Engineering

“…This anomalous phenomenon in xBLZT (x = 1, 2, and 3) is attributable to the nonuniform distribution of Li + during the sintering process. 33,48,49 As can be seen from Figure 6a−c, all of these EC properties under 70 kV cm −1 reach a maximum at 333 K, which is attributable to the ferroelectric−paraelectric transition that can be confirmed by the dielectric shoulder peak presented in Figure 4b. Concurrently, in cooperation with the steep dielectric main peak at the range of 285−295 K for the Li 2 CO 3 -doped ceramic, the variations between ΔT 310 and ΔT 320 (i.e., ΔT v = (ΔT 320 −ΔT 310 )/ΔT 310 ) of xBLZT (x = 1, 2, and 3) at 308− 318 K are 1.2, 1.26, and 1.2, respectively, which are all obviously larger than the BZT with the value of 1.08, leading to a relatively larger ECE at a high-temperature range of 313−343 K. In addition, the trend of EC strength of different components is consistent with its polarization intensity, which adds to the proof that the rhombohedral phase generated via lattice stress provides additional polarization leading to the enhancement of ECE.…”

“…But for bulk BaTiO 3 ceramics, above 2 GPa external stress generated by heavy hydrostatic pressure equipment is required to drive the transition from the tetragonal phase to the cubic phase, which will greatly weaken the practicability of EC bulk ceramics . Comparatively, the internal stress of bulk ceramics constructed via the interface in inhomogeneous structures, such as core–shell and laminated composite structures, is generally regarded as a relatively efficient method to regulate polarization properties. , For example, a laminated composite ceramic composed of three various layers with components of BaTi 0.89 Sn 0.11 O 3 , BaTi 0.85 Zr 0.15 O 3 , and BaTi 0.89 Hf 0.11 O 3 induces internal stress arising from the interface coupling effect between adjacent layers that can be used to enhance the polarizability and ECE. However, to increase the area of the heterogeneous interface, constructing complicated structures in bulk ceramics is needed to generate the interface stress, which will create excessive holes and deteriorate the dielectric breakdown strength.…”

Giant Room-Temperature Electrocaloric Effect of Polymer-Ceramic Composites with Orientated BaSrTiO3 Nanofibers

“…16 Ferroelectric ceramics, whose polarization derives from the ion displacement, can produce large EC strength (the ECE stimulated with a unit electric field, i.e., ΔT/ΔE and ΔS/ ΔE), but their high ECE is limited by the low electric breakdown strength. 4,17 In contrast, ferroelectric polymers can withstand high fields and thus produce large ECE. But its ECE is restricted because the flipping of the polymer chains requires large electric fields.…”

“…However, the low efficiency, large size, and environmental issues have yet to be resolved. The electrocaloric effect (ECE), which refers to the entropy change and temperature change created by the domain switching in ferroelectric materials with external electric fields, can realize high-efficiency cooling. − Without using the compressor and fluorinated refrigerant, EC cooling also features a small size and environmental friendliness, becoming a promising supplement to conventional refrigeration with a compressor, and being a candidate for local cooling, e.g., refrigerating for integrated circuits. − …”

“…Tremendous efforts have been made to investigate the ECE of ferroelectric ceramics and polymers since the high ECE explored in lead zirconate titanate (PZT) ceramic films and poly­(vinylidene fluoride-trifluoroethylene) polymer . Ferroelectric ceramics, whose polarization derives from the ion displacement, can produce large EC strength (the ECE stimulated with a unit electric field, i.e., Δ T/ Δ E and Δ S/ Δ E ), but their high ECE is limited by the low electric breakdown strength. , In contrast, ferroelectric polymers can withstand high fields and thus produce large ECE. But its ECE is restricted because the flipping of the polymer chains requires large electric fields. , Nanocomposites composed of ferroelectric ceramics and polymers are adopted to reconcile the contradiction.…”