We report the effect of configurational entropy (CE) on the electrocaloric (EC) effect of BaxSryCaz(Bi0.5Li0.5)1-x-y-zTiO3 (BSCBLT) (0.627≤x ≤ 0.66, 0.0716≤y ≤ 0.1993, 0.0145≤z ≤ 0.1758) ceramics. ...All samples were designed to show different CE but the same A-site cation average radius, tolerance factor and cationic size disorder. The samples with x ≤ 0.64 show ferroelectric (FE) relaxor behavior, while x ≥ 0.65 are normal FEs. x = 0.65 shows the maximum EC effects among all samples. Both maximum adiabatic temperature change (ΔTm) and CE vary almost in the same way with increasing x. The anomalous enhancement of ΔTm in x = 0.65 with relatively lower CE compared with that in x = 0.64 can be ascribed to an additional contribution of Ba concentration induced FE to relaxor FE transition in BSCBLT. Our results reveal important evidences of enhanced EC effects by CE and suggest that designing FEs or relaxor FEs with high CE might be an effective route to achieve high EC effects.
Lead-free ferroelectric ceramics (1−x)Bi0.5Na0.5TiO3−xKNbO3 (BNT–xKN) with x=0.00, 0.04, 0.06 and 0.08 were synthesized by the conventional solid state reaction method. The effects of the KNbO3 ...addition on the dielectric behavior, ferroelectric properties, as well as electrocaloric effect of the ferroelectric ceramic BNT–xKN were investigated. The results show that the depolarization temperature decreases with the increment of KN content. A high ECE of 1.73°C is achieved at 76°C in BNT–0.06KN. The relation between electrocaloric effect and depolarization transition was discussed. This investigation indicates that the depolarization transition below Curie transition in BNT-based ceramics is a promising approach in ECE technique.
Bi0.5Na0.5TiO3 (BNT)-based relaxors are considered as potential candidates for pyroelectric applications due to their excellent pyroelectric performances. However, the excellent pyroelectric response ...in BNT-based relaxors is generally accompanied by a rapid decrease in the depolarization temperature Td, limiting the operation temperature. Herein, we find that the mixed non-ergodic and ergodic relaxor states (a kind of transition system) can promote polarization rotation and remain the reversibility of polarization transformation simultaneously, thereby improving pyroelectric performances and maintaining the Td . The Li+-doped BNKT-based relaxors which possess such a transition state exhibit excellent room temperature (RT) pyroelectric coefficients (1247 μCm−2K−1), and also, the Td can maintain at 69℃. This work provides a strategy for further insight into the enhanced pyroelectric response, which promotes the development of eco-friendly pyroelectric applications (such as infrared detection, temperature sensors, and pyroelectric energy harvesting).
(Pb0.97La0.02)(Zr x Sn0.94–x Ti0.06)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 (ΔT = −11.5 K) and a large electrocaloric strength (|ΔT/ΔE| = 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.
Abstract
We firstly reported the electrocaloric properties in relaxor (1−
x
−
y
)NaNbO
3
–
y
BaTiO
3
–
x
CaZrO
3
ceramics, and high electrocaloric effect (∆
T
~0.451 K and∣∆
T
/∆
E
∣~0.282 Km/MV) can ...be realized in the ceramics (
x
=
0.04 and
y
=
0.10) under low temperature and low electric field. Relaxor behavior of NaNbO
3
ceramics can be found by doping both BaTiO
3
and CaZrO
3
. In addition, optimized piezoelectric effects (
d
33
~235 pC/N and
d
33
* ~230 pm/V) can be observed in the ceramics (
x
=
0.04 and
y
=
0.10) due to the involved morphotropic phase boundary (
MPB
). Excellent piezoelectric effect (ie,
d
33
~330 pm/V at 41°C, and
d
33
*~332 pm/V at 60°C) can be found because of the characteristics of
MPB
. Good temperature reliability of piezoelectric effect can be shown because of both
MPB
and relaxor behavior. We believe that the ceramics with high electrocaloric effect and good piezoelectric effect can be considered as one of the most promising lead‐free materials for piezoelectric devices.
One of the emerging solid-state refrigeration technologies to replace classic compression refrigeration is electrocaloric refrigeration, which has the advantages of high energy conversion efficiency, ...easy miniaturization, eco-friendliness, and low cost. In this paper, Ba(Ti1−xSnx)O3 (BTSn) ceramics with x = 0.02–0.08 were prepared by a solid-state reaction route. The structural, dielectric, ferroelectric, electrocaloric as well as electrostrictive characteristics were thoroughly examined. Our results show that the dielectric peaks correlated to the maximal permittivity move towards to low temperature direction when the Sn4+ concentration gradually increases, and a phase diagram of BTSn based on the dielectric characteristics is given. More importantly, in the x = 0.04 ceramic sample synthesized by the viscous polymer process, a giant adiabatic temperature change (ΔT) of 6.36 K with a temperature range of 25 °C at 200 kV/cm is achieved. Typically flare shape electrostrain curves accompanying with small hysteresis are observed in all studied compositions. The average electrostrictive coefficient Q33 varies within 0.0257–0.0306 m4/C2 at a temperature region from 30 to 160 °C, indicating temperature-insensitive and composition-insensitive characteristics. This research shows that a significant electrocaloric effect can be achieved in BTSn ceramics through high electric field, and would provide a strategy for boosting the electrocaloric effect in other systems.
The electrocaloric effect has been investigated in Sr and Nb co-doped Pb(Zr,Ti)O3 (PSNZT) ceramics synthesized by conventional solid state reaction. The coexistence of negative and positive ...electrocaloric effect was revealed in PSNZT ceramics. The electrocaloric response values of −0.38K at 80°C and 0.65K at 180°C were observed under an electric field of 1.5kV/mm. The corresponding electrocaloric coefficient values were calculated to be −0.25KmmkV−1 and 0.43KmmkV−1 respectively. The mechanism of the coexistence of negative and positive electrocaloric effect was discussed.
•Sr and Nb co-doped Pb(Zr,Ti)O3 ferroelectric ceramics were synthesized by a solid-state reaction method.•Rare phenomenon of coexistence of negative and positive electrocaloric effect was found in Sr and Nb co-doped Pb(Zr,Ti)O3 ferroelectric ceramics.•High electrocaloric coefficient of −0.25KmmkV−1 and 0.43KmmkV−1 were obtained.•Reason for the coexistence of negative and positive electrocaloric effect was discussed.
Barium zirconate titanate (BZT) (Ba(Zr x Ti1–x )O3) ceramics with Zr4+ contents of x = 5, 10, 15, 20, 25, and 30 mol % were prepared using a solid-state reaction approach. The microstructures, ...morphologies, and electric properties were characterized using X-ray diffraction, scanning electron microscopy, and impedance analysis methods, respectively. The dielectric analyses indicate that the BZT bulk ceramics show characteristics of phase transition from a normal ferroelectric to a relaxor ferroelectric with the increasing Zr4+ ionic content. The electrocaloric effect adiabatic temperature change decreases with the increasing Zr4+ content. The highest adiabatic temperature change obtained is 2.4 K for BZT ceramics with a 5 mol % of Zr4+ ionic content.
