Large Electrocaloric Effect in (Bi_0.5Na_0.5)TiO₃-Based Relaxor Ferroelectrics

Abstract

The electrocaloric effect (ECE) is significantly critical for environmentally friendly cooling technologies to replace vapor compressionbased refrigeration. Lead-free bismuth sodium titanate-based ferroelectrics have attracted considerable attention because of their depolarization process, which can induce a high ECE. However, their high depolarization temperature (T d ) disobeys the principle of room temperature (RT) cooling. Considerable efforts have been devoted to the shift of T d to near RT via chemical doping, while the corresponding ferroelectric properties of the materials are sacrificed. Herein, we design a relaxor ferroelectric {[Bi 0.5 (Na 0.72 K 0.18 Li 0.1 ) 0.5 ] 1−x Sr x }TiO 3 (BNKLS x T) ceramic system which shows a decreased T d toward RT, and a high ECE (adiabatic temperature change of 2.51 K and electrocaloric coefficient of 0.386 K mm kV −1 ) is achieved when the measurement temperature approaches the T d . This high ECE performance outperforms most reported lead-free ceramics and even behaves better than 0.9Pb(Mg 1/3 Nb 2/3 )O 3 -0.1PbTiO 3 ceramics. The superior ECE behavior is ascribed to the enhanced maximum polarization (P max ) resulting from the addition of Sr and the existence of the depolarization process. Piezoresponse force microscopy results verify that the increased P max originates from the decreased domain size and the increased density of the domain in BNKLS x T. This work not only offers us an attractive lead-free ferroelectric material for ECE coolers but also opens a new direction toward the rational design of ceramics for ECE.

Room‐Temperature Symmetric Giant Positive and Negative Electrocaloric Effect in PbMg0.5W0.5O3 Antiferroelectric Ceramic

“…Figure 5e compares the ECE ΔT and corresponding transition temperatures of typical FE/AFE bulk materials studied in the literature. [11,15,19,20,30,31,[39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58] Similar caution applies to calculations of false negative ECEs. [20,37,38,52,59] There are very few examples in the literature of FE materials with giant ECE near room temperature.…”

“…This has seriously limited, if not hindered, the practical applications of FE refrigeration. Although [19,20,30,31,[39][40][41]58] [ : BaTiO 3 -based bulks, [11,[42][43][44][45][46][47] : Na 0.5 Bi 0.5 TiO 3 -based bulks, [51][52][53][54][55][56] : (K,Nb)NbO 3 -based bulks, [15,[48][49][50] : BiFeO 3 -based bulk, [57] : PMW ceramic. f) The maximum entropy changes and corresponding temperature changes of positive and negative ECEs under different electric fields.…”

“…e) Comparison of the ECE temperature change of PMW ceramic with representative FE/AFE bulk materials under different temperatures. : Pb(Zr,Ti)O 3 -based bulks,[19,20,30,31,[39][40][41]58] [ : BaTiO 3 -based bulks,[11,[42][43][44][45][46][47] : Na 0.5 Bi 0.5 TiO 3 -based bulks,[51][52][53][54][55][56] : (K,Nb)NbO 3 -based bulks,[15,[48][49][50] : BiFeO 3 -based bulk,[57] : PMW ceramic. f) The maximum entropy changes and corresponding temperature changes of positive and negative ECEs under different electric fields.…”

Large electrocaloric effect under electric field behavior in potassium sodium niobate ceramics with incompletely overlapped phase boundaries

“…[8][9][10][11] Based on the demands of environmentally friendly development, the ECE of lead-free ferroelectrics has also been emphasized with typical examples of BaTiO 3 (BT) and (Na,Bi)TiO 3 (BNT)-based materials because of the strong ferroelectricity with diversied phase structures of BT and the existence of depolarization temperature (T d ) of BNT, respectively. [12][13][14][15][16][17][18][19][20] However, scarce attention has been paid to another lead-free ferroelectric, potassium sodium niobate [(K,Na)NbO 3 , KNN], even though it also has strong ferroelectricity and plentiful phase boundaries. 21,22 Notably, ceramics with relatively simple preparation technology and low cost more sufficiently meet the necessary cooling system compared to lms and crystals.…”

Enhanced electrocaloric effect in compositional driven potassium sodium niobate‐based relaxor ferroelectrics

“…5(a)-5(d), in which (∂P/∂T ) E is procured from the fourth-order polynomial fitting of the virgin P max −T curves [12]. It is clear that the enhanced ΔT values can be observed in the ceramics with x = 0.08−0.15 when the applied external electric field increases due to the optimal ordered state under the high electric fields [35]. In addition, the ECE peak gradually shifts to a lower temperature when x increases from 0.08 to 0.15, well matching the decreased T C values with increased x content (Fig.…”