Different doping elements have been used to reduce the dielectric losses of CaCu3Ti4O12 ceramics, but their dielectric constants usually are undesirably decreased. This work intends to reduce their ...dielectric losses and simultaneously enhance their dielectric constants by co-doping Y3+ as a donor at A site and Al3+ as an acceptor at B site for substituting Ca2+ and Ti4+, respectively. Samples with different doping concentrations x=0, 0.01, 0.02, 0.03, 0.05 and 0.07 have been prepared. It has been shown that their dielectric losses are generally reduced and their dielectric constants are simultaneously enhanced across the frequency range up to 1MHz. The doped sample with x=0.05 exhibits the highest dielectric constant, which is well over 104 for frequency up to 1MHz and is about 20% higher than the undoped sample. Impedance spectra indicate that the doped samples have much higher grain boundary resistance than the undoped one.
Dielectric ceramics with high recoverable energy storage density (Wrec) and high energy storage efficiency (η) are urgently needed due to their potential application in pulse capacitor devices. ...However, the low η and breakdown strength (BDS) have produced a bottleneck for achieving high Wrec at high electric field. Here, we introduce Bi(Mg0.5Ti0.5)O3 (BMT) into Ba(Ti0.92Sn0.08)O3 (BTS) matrix to enhance the relaxor character of BTS–xBMT and reduce the electrostrictive strain generated during electric field loading. The enhanced relaxor character is beneficial for increasing the efficiency, whereas the reduced electrostrictive strain is profitable to increase the BDS. Furthermore, the BDS is significantly improved by the polymer viscous rolling process. Finally, the electrostrictive effect was considerably lowered in an optimized BTS–0.1BMT composition. More crucially, a high Wrec of 4.34 J/cm3 was attained accompanied by excellent temperature stability (variation ≤±5% between 30 and 120°C). The current results show that the developed dielectric ceramics can be used in pulse capacitor devices for energy storage.
In the past decades, lead-free ceramics with high polarization, low remnant polarization and high electric breakdown strength have drawn a lot of attention because of their potential applications in ...dielectric capacitors with excellent energy storage performance. In the current investigation, we develop a novel lead-free Dy doped 0.5Na
0.5
Bi
0.5
TiO
3
–0.5SrTiO
3
ceramics, which were fabricated by the conventional electroceramic processing route. By doping Dy
2
O
3
into 0.5Na
0.5
Bi
0.5
TiO
3
–0.5SrTiO
3
with various contents from 0.1 at.% to 0.5 at.%, pure perovskite phases and relatively dense structures were obtained. The increase of Dy
2
O
3
concentration not only shifts the
T
m
toward to lower temperature, but also reduces the permittivity and gain sizes, thus enhancing the temperature stability of dielectric properties. The enhanced dielectric energy storage properties were systematically investigated by testing the polarization–electric field hysteresis loops as a function of the applied electric field, temperature, and loading cycles. The dielectric energy storage density of in 0.1 at.% doped 0.5Na
0.5
Bi
0.5
TiO
3
–0.5SrTiO
3
is 1.59 J/cm
3
, which is nearly twice higher than that of undoped NBT–ST. Hence, the Dy modified 0.5Na
0.5
Bi
0.5
TiO
3
–0.5SrTiO
3
ceramics have exhibited potential application as dielectric capacitors with relatively good energy storage performance.
Lead free 0.5Na0.5Bi0.5TiO3-0.5SrTiO3 ceramics with Bi excess (NB0.5+xT-ST) were prepared by a conventional solid-state reaction method. The effects of bismuth excess on microstructure, dielectric ...properties and energy storage performances of NB0.5+xT-ST ceramics were investigated systematically. The results show that all ceramics exhibit a perovskite structure with excess Bi doping, the grain size decreased and density enhanced. Typical relaxor ferroelectric P-E hysteresis loops were observed with introduction of Bi2O3. The sample with Bi2O3 excess concentration of 1 mol% exhibits the maximum energy storage density 1.05 J cm−3, which is 2 times higher than that of pure NBT-ST. Meanwhile, the sample displays a high current density of 245.6 A cm−2 and a power density of 6.5 MW cm−3. These results indicate that the Bi2O3 excess improved NB0.5+xT-ST ceramics are useful for potential applications in energy storage ceramic capacitors.
A B-site acceptor doping strategy has been employed to fabricate Na0.25Sr0.5Bi0.25TiO3 (NSBT-xM) relaxor dielectric ceramics for the purpose of obtaining predominant energy storage properties for ...pulsed power capacitor applications. MgO was selected as the acceptor additive, and the corresponding ceramics were designed and prepared by traditional preparation method of electronic bulk ceramic. The influence of MgO on the micro structure, surface micromorphology, the variation of dielectric properties and storage of electrical energy, and also the mechanism of the NSBT-xM samples were deeply and systematically studied. The substitution of Ti4+ by Mg2+ at B-site induces point defects companied with defect diploe PD, which influences the electrical properties dramatically. Appropriate amount of MgO can significantly increase the electrical breakdown strength and reduce Pr, which is conducive to the improvement of energy storage performance. Particularly, the NSBT-0.25 M sample exhibits both high Wrec (2.06 J/cm3) and excellent efficiency (84%) spontaneously. It also exhibits fantastic frequency stability, fatigue endurance, and excellent charge and discharge performance.
Recently, ferroelectric ceramics with high maximum polarization, low remnant polarization and high electric breakdown strength (BDS) have attracted much attention due to their potential applications ...in energy storage capacitors. In this work, we show a novel kind of (Ba,Sr)TiO3 (BST)-based lead-free ferroelectric ceramics, i.e., (1-x)Ba0.9Sr0.1TiO3-xBi(Zn0.5Zr0.5)O3 (BST-xBZZ) solid solutions, which were fabricated by the traditional solid-state reaction process. By introducing the BZZ into BST with a content from 0.05 to 0.20, purely pseudocubic perovskite phases and highly dense structures are obtained. The increase of the BZZ content not only shifts the TC toward to lower temperature, but also induces strong relaxor behaviors with diffuse phase transition characteristics, thus improving the temperature stability of dielectric properties. Of special interest is the improved energy storage properties, which were systematically evaluated by measuring the polarization-electric field (P-E) hysteresis loops as a function of electric field, frequency and loading cycle. It is found that BT-0.15BZZ ceramic achieves a maximum energy density of 1.11 J/cm3, which is attributed to the improvement of BDS. In addition, relatively good frequency stability and fatigue resistance of this composition suggest its potential application in energy storage devices.
In this study, environmentally friendly Bi-substituted (Ba0.85Ca0.15)1-3x/2Bix(Zr0.1Ti0.9)O3 (BCZT-xBi) ferroelectric ceramics with x = 0–0.08 were prepared using a solid-state sintering method. The ...structures, dielectric, electrostrictive and electrocaloric properties of the Bi-substituted BCZT ceramics were thoroughly investigated. With an increase in the Bi3+ content, the temperature corresponding to the maximum permittivity (Tm) decreased monotonously. Meanwhile, the broadening of the dielectric peaks and the increase in the relaxation coefficient of the ceramics transformed their typical ferroelectric-to-paraelectric phase transition to diffuse phase transition (DPT). This was further confirmed by the trends shown by the ferroelectric properties of the ceramics. The current peak intensity in current-electric field (I-E) curves decreased with an increase in x and finally became constant, indicating that domain reversal disappeared gradually. High electrostrictive coefficient Q33 values of 0.0307, 0.0299 and 0.0223 m4/C2 were obtained for the ceramics with x = 0.02, 0.04 and 0.06 respectively. The Q33 values of the ceramics indicated their temperature-insensitive nature over the temperature range of 30–120 °C. Although the maximum value of the electrocaloric adiabatic temperature change (ΔT) (0.91 K) was achieved at x = 0.02, the thermally stability of ΔT is improved with an increase in x from 0.02 to 0.06. The results indicated that x = 0.06 improved the thermal stability of the electrostrictive and electrocaloric performance. By increasing the driving field strength, better electrostrictive and electrocaloric responses could be achieved.
Lead-free relaxor bulk ceramics (LFRBCs) have the advantages of environment-friendliness, diffuse phase transition near room temperature (RT) and large heat absorption capacity, so as to be ...candidates for medium and large electric refrigeration and cooling equipment. Although considerable efforts have been made to explore LFRBCs with a large adiabatic temperature change (ΔT) near room temperature, the RT ΔT of LFRBCs is still too weak, baffling their practical applications. In addition, common strategy for achieving a large RT ΔT is mainly tuning phase transitions by compositional engineering. Unfortunately, this strategy is not enough to realize the required properties for EC cooling devices. In this work, based on the general phenomenological expressions of EC effect, we proposed a new strategy, i.e. coordinated regulation of phase transitions and applied electric fields, to achieve a large RT ΔT and a wide using temperature range in LFRBCs simultaneously. Encouragingly, the ΔT calculated using the indirect method inclines from 0.96 K to 1.7 K ranging from 300 K to 360 K in 0.25 mol. % La3+ doped Ba(Zr0.2Ti0.8)O3 ceramic under electric field change of 150 kV cm−1, which is much higher than that calculated using the indirect method so far in many LFRBCs designed using previous strategy for EC refrigeration, demonstrating a big step in LFRBCs for EC refrigeration. The large RT ΔT and broad operating temperature range are mainly attributed to diffuse phase transition near room temperature and a high applied electric field. Most importantly, this work provides a significant guideline to develop new LFRBCs with high comprehensive EC properties for high-efficiency cooling devices, which will bring a series of new LFRBCs with a large room-temperature ΔT in a wide temperature range for next-generation refrigeration in the future.
Zr-substituted (Bi0.5Na0.5)(Ti1−xZrx)O3 (BNTZ) with x = 0.02–0.4 ceramics were prepared using solid-state reaction technique and their structural, dielectric and ferroelectric properties were ...investigated systematically. X-ray diffraction results suggest that Zr4+ ion can enter the (Bi0.5Na0.5)TiO3 (BNT) crystal lattices at a limited value and a secondary phase appears in BNTZ ceramics when the x exceeds 0.1. Temperature-dependent dielectric permittivities of BNTZ ceramics show only one dielectric peak from room temperature to 500 °C for each composition, and this dielectric peak becomes broad gradually as x increases from 0.02 to 0.4. The permittivity of x = 0.4 varies less than ±10% between room temperature and 300 °C, indicating a superior thermal stability of the permittivity. Polarization enhancement is revealed by the polarization-electric field hysteresis loops and highest ferroelectric properties are obtained in x = 0.04. The electric-field-induced strains of x = 0.04 show a monotonous increase as temperature increases from 30 °C to 150 °C. At 80 kV/cm, a high strain level of 0.268% is achieved. Our results suggest that the introduction of Zr4+ ion could effectively tailor the dielectric and ferroelectric properties of BNT ceramics and x = 0.4 composition could find potential application in high temperature capacitor devices.
Due to requirements for miniaturization and integration of electronic devices, ferroelectric materials with high dielectric permittivity would have potential applications in dielectric capacitors. In ...this work, (1−x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT) powders with x from 0.10 to 0.30 were obtained on the basis of a transitional columbite precursor method, while sintering processes were carried out under three protocols, i.e., (I) 1230 °C for 2 h, (II) 1230 °C for 16 h and (III) 1250 °C for 2 h. The temperature-dependent dielectric properties measured from 25 °C to 225 °C show that, under protocols II and III, the maximum permittivity (εm) is significantly improved compared to those obtained via protocol I. A maximum εm of 47036 is obtained in x = 0.25 composition under protocol II, and the εm is increased by more than 90% at the same composition. In the ceramics sintered through protocols II and III, the characteristics of both dielectric relaxations and dielectric dispersions are also enhanced. In addition, the ferroelectric and piezoelectric properties also show a marked increase in the composition of x = 0.3. Our results suggest that the dielectric and ferroelectric properties of PMN-xPT solid solutions could be effectively enhanced by controlling the sintering protocols.
