Ferroelectric ceramics have good piezoelectric and ferroelectric properties and can be used for energy storage equipment and actuators. Nevertheless, current research on dielectric capacitors has ...only focused on the energy storage density, but ignored efficiency. Moreover, conventional piezoelectric materials have a large strain hysteresis. In this work, (Al0.5Nb0.5)4+ (AN) complex ions doped 0.7Bi0.5Na0.5TiO3-0.3Ba0.3Sr0.7TiO3 (BNBST) ceramics were prepared. Doping AN destroyed the long-range ordered ferroelectric domains and generated polar nano regions, resulting in a gradual thinning and inclination of polarization hysteresis loops and an increase in relaxor degree. For BNBST-3AN ceramics, a Wrec of 1.52 J/cm3 and a η of 92.1% were achieved at 150 kV/cm. Meanwhile, BNBST-3AN ceramics had good energy storage temperature stability and cycling performance. The AN doping reduced the strain hysteresis in BNBST ceramics. BNBST-2AN ceramics exhibited a longitudinal electrostrictive coefficient Q33 ∼ 0.0292 m4/C2 and a field-induced strain of 0.25% with low strain hysteresis (6.67%). Furthermore, BNBST-4AN ceramics had superior dielectric temperature stability from 24 to 270 °C. All results show that BNBST-100xAN ceramics have great promise for energy storage devices and actuators.
Lead-free relaxor ferroelectric ceramics are potential for energy storage applications due to their comprehensive energy storage properties. However, the energy efficiency of many relaxor ceramics is ...not high enough, leading to high Joule heat during the charge–discharge cycles, thus lowering their energy storage performance. In this work, tantalum (Ta) dopants were introduced into sodium niobate-based relaxor ceramics to improve the resistivity and energy efficiency. The leakage current was reduced by Ta doping, especially at the high electric field. The enhanced resistivity is attributed to the increased bandgap induced by Ta doping. The impedance spectroscopy shows that both the grain and grain boundary resistivities are improved in the high temperature region. As a result, the optimal recoverable energy density and energy efficiency are 6.5 J/cm3 and 94% at 450 kV/cm, respectively. In addition, the energy storage properties exhibit satisfactory temperature stability and cycling reliability. All these merits demonstrate that the Ta modified sodium niobate-based relaxor ceramic a potential candidate for high-power energy storage applications.
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•A novel Bi1/2K1/2TiO3-based ergodic relaxor ceramic was designed and prepared .•The ceramic displayed large Wrec (3.07 J/cm3) and high η (>88%).•The variation of Wrec is less ...than ±2% between 30 and 150 °C.
Relaxor ferroelectrics are attractive for the high energy storage density. However, the polarization responses of most relaxor ferroelectrics are sensitive to temperature, thus leading to thermal-dependent energy storage properties. In this work, 0.5Bi1/2K1/2TiO3–0.5SrTiO3 (0.5BKT–0.5ST) and 0.95(0.5Bi1/2K1/2TiO3–0.5SrTiO3)–0.05Bi(Zn1/2Ti1/2)O3 (BKT–ST–0.05BZT) ceramics were prepared using the solid-state reaction method. Both compositions showed an average cubic structure, with a relaxor-type dielectric anomaly. The rather low remanent polarization and delayed saturated polarization indicated the formation of the ergodic polar nano regions. Benefitting from the Bi(Zn1/2Ti1/2)O3 modification, the recoverable energy storage density (Wrec) reached 3.07 J/cm3 because of the enhanced polarization and increased bandgap. Meanwhile, BKT–ST–0.05BZT exhibited a high storage efficiency (η > 88%). When the specimen was heated from 30 °C to 150 °C, Wrec under the maximum electric field Em of 150 kV/cm varied from 1.58 to 1.63 J/cm3 (＜ ±2%).
In this study, a series of high-entropy lead-free relaxor ferroelectrics (1-x)(Bi0.4Na0.2K0.2Ba0.2)(Ti0.95Zr0.05)O3–xSr(Mg1/3Nb1/3Ta1/3)O3 are designed and synthesized. As x increases, the ...corresponding configurational entropy (∆Sconfig) varies from 1.53 R to 2.10 R. The long-range ordered structure of the ferroelectric domains is disrupted, accompanied by the reduced remanent polarization (Pr) and the improved Wrec. When x = 0.09, a high recoverable energy density Wrec of 3.83 J/cm3 and a high energy storage efficiency η of 85.7 % were obtained at an electric field of 360 kV/cm. In addition, the 0.91BNKBTZ-0.09SMNT ceramic sample has excellent performance stability under different temperatures (30–180 °C), cycle times (1–104 times) and frequencies (1–100 Hz), making it a reliable candidate as a dielectric for pulsed power systems.
•High-entropy BNKBTZ-SMNT ceramics for dielectric energy storage were design and prepared.•A high Wrec of 3.83 J/cm3 and high η of 85.7 % at 360 kV/cm were achieved.•The excellent stability in energy storage has been achieved in 0.91 BNKBTZ-0.09SMNT.
This model discussion focuses on links between the unique properties of relaxor ceramics and the basics of Critical Phenomena Physics and Glass Transition Physics. It indicates the significance of ...uniaxiality for the appearance of mean-field type features near the paraelectric-to-ferroelectric phase transition. Pretransitional fluctuations, that are increasing up to the size of a grain and leading to inter-grain, random, local electric fields are responsible for relaxor ceramics characteristics. Their impact yields the pseudospinodal behavior associated with "weakly discontinuous" local phase transitions. The emerging model redefines the meaning of the Burns temperature and polar nanoregions (PNRs). It offers a coherent explanation of "dielectric constant" changes with the "diffused maximum" near the paraelectric-to-ferroelectric transition, the sensitivity to moderate electric fields (tunability), and the "glassy" dynamics. These considerations are challenged by the experimental results of complex dielectric permittivity studies in a Ba
Sr0.
TiO
relaxor ceramic, covering ca. 250 K, from the paraelectric to the "deep" ferroelectric phase. The distortion-sensitive and derivative-based analysis in the paraelectric phase and the surrounding paraelectric-to-ferroelectric transition reveal a preference for the exponential scaling pattern for
(
) changes. This may suggest that Griffith-phase behavior is associated with mean-field criticality disturbed by random local impacts. The preference for the universalistic "critical & activated" evolution of the primary relaxation time is shown for dynamics. The discussion is supplemented by a coupled energy loss analysis. The electric field-related tunability studies lead to scaling relationships describing their temperature changes.
In this work, lead-free energy storage ceramics, (1−x)(0.95Bi
0.5
Na
0.5
TiO
3
-0.05Ba
0.85
Ca
0.15
Zr
0.1
Ti
0.9
O
3
)-xSr
0.7
La
0.2
SnO
3
(BNT-BZCT-xSLS, x = 0.05, 0.10, 0.15, and 0.20), were ...prepared. The crystal structure, microstructure, dielectric properties, ferroelectric properties, energy storage properties, and charge-discharge performance of BNT-BZCT-xSLS were systematically studied. Among the products, BNT-BZCT-0.15SLS exhibited the highest energy storage performances (W = 2.95 J/cm
3
, W
rec
= 2.09 J/cm
3
, and η = 71%) due to its dense microstructure, finer grain size, and improved relaxation. Furthermore, the BNT-BZCT-0.15SLS also showed an ultra-fast charge and discharge speed (t
0.9
= 0.033 μs) and a large power density (P
D
= 28.0 MW/cm
3
).
Based on the experimental data of the isothermal polarization
P
(
T
,
E
) of BaHf
0.11
Ti
0.89
O
3
bulk ceramic, entropy change (∆
S
), temperature change (∆
T
), and heat carrying capacity (∆
Q
) of ...the material are evaluated in detail using an artificial neural network (ANN) procedure. As a result, the maximum ECE occurs above
T
C
and shifts to higher temperatures with increasing applied field. The BaHf
0.11
Ti
0.89
O
3
ceramic exhibits large ECE parameters around the Curie temperature (
T
C
) associated with a relatively broad electrocaloric temperature span. Furthermore, under different electric fields, many figures of merit such as relative cooling power, temperature-averaged entropy change, and normalized refrigerant capacity are explored, making the sample a promising material for green cooling devices. Such figures of merit increase monotonically with the enhancement of the applied field. In addition, the field dependence of the ∆
S
and ∆
T
is thoroughly investigated. The master curve and the exponent n controlling the field dependence of both magnitudes confirm the second-order character of the electric phase transition of the sample. The ANN method provides very accurate and fast predictions with a small amount of experimental data. Therefore, this method accelerates the characterization of novel electrocaloric materials by shortening the time necessary for experimentation.
Solid-state refrigeration using the electrocaloric effect (ECE) in ferroelectric materials is a promising alternative to the conventional vapor-compression technology. In spite of growing interest to ...the investigation of the ECE, direct measurements of the effect are still rare. In this paper, we report on a modification of a differential scanning calorimeter for direct ECE measurements. The importance of proper estimation of the thermal correction factor and use of proper values of the heat capacitance for correct ECE measurements is discussed. The ECE measurements were performed for Ba(Zr 0.2 Ti 0.8 )O 3 and Ba(Zr 0.12 Ti 0.88 )O 3 bulk ceramics. Large electrocaloric temperature changes of 0.54 and 0.34 K are achieved under the application of an electric field of 2 kV/mm for the Ba(Zr 0.12 Ti 0.88 )O 3 and Ba(Zr 0.2 Ti 0.8 )O 3 samples, respectively. The relation between the directly measured ECE values and frequently used indirect estimation based on Maxwell's relations is discussed.
Lead free ceramics Ba1−xLn2x/3Zr0.3Ti0.7O3 (Ln = La, Nd, Sm, Eu and Sc), x = 0.02-0.10 are investigated for electrostrictive effect and energy storage properties in the proximity of ...relaxor-paraelectric phase boundary. Relaxor phase evidence from slim hysteresis loop and low remnant polarization are the key parameters responsible for improve the electrostrictive effect and energy storage properties simultaneously. With increase in rare earth content negative strain disappeared and almost hysteresis free strain is achieved. Strain-hysteresis profile in term of S-E, S-E2 and S-P2 is used to analyze the electrostrictive behavior of these ceramics. An average strain (S%) ∼ 0.03%, is accomplished at initial concentrations of x = 0.02-0.04 and electrostrictive coefficients (Q11, and M11) as well as the energy storage density is improved by a factor of 1.2 and 2.6 respectively when compare with pure (x = 0.0) ceramic. Above x ≥ 0.06, all compositions show a stable behavior which suggested the possibilities of these relaxor ceramics towards high precision actuators and energy storage application.
Ba(Nd
0.1
Ti
0.8
Nb
0.1
)O
3
(1-y)
Na
0.5
Bi
0.5
TiO
3
y
ceramics were prepared through solid state sintering (CS) and microwave sintering (MWS) route. The XRD results indicate that the ceramic ...samples have a cubic structure at room temperature. The dielectric, electromechanical and piezoelectric properties were also investigated. Relaxor behaviour was observed for the present ceramic samples prepared through both the sintering routes. The degree of diffusiveness of phase transition and relaxor behaviour are more for CS ceramic when compared to MWS ceramic with y = 0.40. From modulus measurements, the values of K
t
, K
eff
and d
33
at 623 K were 0.99983, 0.99980 and 5.273 nm.V
−1
respectively for MWS ceramic with y = 0.25. The piezoelectric constant (d
33
) decreased with the increase of temperature. The d
33
values are higher for the microwave sintered ceramic samples when compared to conventional sintered ceramic samples.
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