Large Electrocaloric Effect in Lead-free Ba(Hf_xTi_1–x)O₃ Ferroelectric Ceramics for Clean Energy Applications

Abstract

Ba­(Hf x Ti1–x )­O3 ferroelectric ceramics were prepared by a conventional solid-state reaction process, and the correlation of structure, dielectric, ferroelectric, and electrocaloric properties were studied. The consequences indicated that the T C of Ba­(Hf x Ti1–x )­O3 ceramics decreased, while T T–O and T O–R increased with the increase of hafnium content. Large electrocaloric effect values of 1.64 K (117 °C) and 1.21 K (76 °C) were observed for Ba­(Hf x Ti1–x )­O3 with x = 0.05 compositions. And, corresponding electrocaloric coefficients respectively were 0.33 and 0.24 K·mm·kV–1. In addition, compared with the second-order phase transition region, larger electrocaloric coefficients (ΔT f /ΔE ≥ 0.19 K·mm·kV–1) were obtained in the first-order phase transition region for all compositions. Meanwhile, the maximum values of electrocaloric coefficients ΔT f /ΔE = 0.38 K·mm·kV–1 was achieved in a smaller electric field for Ba (Hf x Ti1–x )­O3 with x = 0.03 compositions.

Phase structure analysis and pyroelectric energy harvesting performance of Ba(HfxTi1‐x)O3 ceramics

“…In particular, only one gentle hill (around the ferroelectric rhombohedral phase to paraelectric cubic phase ( T C )) at 64°C is acquired in the BHT12 sample. The above results show that the T C of Ba(Ti 1‐ x Hf x )O 3 ceramics gradually decreases with increasing Hf doping content but T T‐O increases, which is confirmed in our early work . On the other hand, the peak position of the dielectric loss of Ba(Ti 1‐ x Hf x )O 3 ceramics presents a region of sharp variation in the dielectric constant.…”

“…The Ba(Ti 1‐ x Hf x )O 3 ( x = 0, x = 5% and x = 12% abbreviated as BT, BHT5 and BHT12, respectively) ceramics were prepared by a conventional solid‐state reaction method. The detailed process and partial list of instruments of characterization are presented in our previous work . The crystal structures of the ceramics were carried out by an XRD system (Bruker, D8 ADVANCE).…”

Analogical discovery of disordered perovskite oxides by crystal structure information hidden in unsupervised material fingerprints

“…Some perovskites such as ferroelectrics display temperaturedependent phase transitions. There can also be coexisting phases at the same temperature 39 . We emphasize that chemical composition is not duplicated in our database, leading to an elimination of additional phases, if there are any.…”

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

“…Pure BaTiO 3 bulk ceramics have sharp first-order ferroelectric-paraelectric (FE-PE) phase transition at T c ∼ 120 °C, which endows it with maximized Δ T value (∼0.4–1.4 K) near T c . , However, the low room-temperature ECE and narrow operation temperature range seriously hindered its commercialization into EC devices which are expected to preferably work at room temperature. Chemical modification strategies through substitution and doping have been proved to be an effective way to shift T c and tailor ECE in BaTiO 3 -based ceramics. − For example, T c values of Ba­(Zr 0.25 Ti 0.75 )­O 3 , (Ba 0.65 Sr 0.35 )­TiO 3 , and (Ba 0.94 La 0.04 )­TiO 3 ceramics were all shifted toward room temperature, with maximized Δ T values about 0.2–1.5 K achieved near there. Until now, despite remarkable progress made through chemical modification strategies, there are still two challenges in BaTiO 3 based ceramics for electrocaloric applications.…”

“…Until now, despite remarkable progress made through chemical modification strategies, there are still two challenges in BaTiO 3 based ceramics for electrocaloric applications. On one hand, as a result of the fundamental limitation, broader EC operation temperature range was always gained at the cost of ECE values, and vice versa. − For example, Δ T peak values decreased by more than 50% in Ba­(Zr, Ti)­O 3 and (Ba, Ca)­(Hf, Ti)­O 3 , ceramics with widening EC temperature usage range. On the other hand, low breakdown electric fields of bulk ceramics make it very challenging to increase Δ T values over 2.0 K. − ,− These disadvantages seriously hindered the implementation of BaTiO 3 -based ferroelectrics in high-efficiency solid-state cooling applications.…”