Bi0.5Na0.5TiO3-BaTiO3-K0.5Na0.5NbO3:ZnO relaxor ferroelectric composites with high breakdown electric field and large energy storage properties

0.82[0.94Bi_0.5Na_0.5TiO₃-0.06BaTiO₃]-0.18K_0.5Na_0.5NbO₃:xZnO (BNT-BT-KNN:xZnO, x?=?0-0.40) relaxor composites were prepared and their electrical properties were investigated. The breakdown electric field increases with increasing ZnO content. For x?=?0 and x?=?0.40 samples, the maximum recoverable energy storage density is 0.74?J/cm³ and 1.03?J/cm³ while the maximum energy storage efficiency is 86.7% and 72.7% under the electric field of 9.0?kV/mm and 14.0?kV/mm, respectively. The recoverable energy storage density and efficiency of the composite vary less than 2.5% from 25?°C to 125?°C, which indicates temperature-insensitive energy storage performance. These results are discussed based on the ZnO-enhanced bulk resistivity and the ZnO-induced local electric field which suppresses the evolution of polar nanoregions.     

High energy storage properties of lead-free Mn-doped (1-x)AgNbO3-xBi0.5Na0.5TiO3 antiferroelectric ceramics

In this work, 0.2 wt.% Mn-doped (1-x)AgNbO₃-xBi_0.5Na_0.5TiO₃ (x = 0.00–0.04) ceramics were synthesized via solid state reaction method in flowing oxygen. The evolution of microstructure, phase transition and energy storage properties were investigated to evaluate the potential as high energy storage capacitors. Relaxor ferroelectric Bi_0.5Na_0.5TiO₃ was introduced to stabilize the antiferroelectric state through modulating the M₁-M₂ phase transition. Enhanced energy storage performance was achieved for the 3 mol% Bi_0.5Na_0.5TiO₃ doped AgNbO₃ ceramic with high recoverable energy density of 3.4 J/cm³ and energy efficiency of 62% under an applied field of 220 kV/cm. The improved energy storage performance can be attributed to the stabilized antiferroelectricity and decreased electrical hysteresis ΔE. In addition, the ceramics also displayed excellent thermal stability with low energy density variation (<6%) over a wide temperature range of 20−80 °C. These results indicate that Mn-doped (1-x)AgNbO₃-xBi_0.5Na_0.5TiO₃ ceramics are highly efficient lead-free antiferroelectric materials for potential application in high energy storage capacitors.     

Bi0·5Na0·5TiO3–Sr0.85Bi0·1TiO3 ceramics with high energy storage properties and extremely fast discharge speed via regulating relaxation temperature

Bi_0·5Na_0·5TiO₃-based relaxor ferroelectric ceramics have recently gained increasing attention due to their outstanding energy storage properties. However, the trade-off between the recoverable energy storage density/efficiency and discharge rate resulted from the hysteresis of domain switching process, severely limits their applications. Herein, a strategy realizing synergistic excellent energy storage properties and fast discharge rate is proposed through regulating relaxation temperature. The relaxation temperature was decreased to below room temperature by introducing Sr_0·85Bi_0·1TiO₃ into Bi_0·5Na_0·5TiO₃ [(1-x)Bi_0·5Na_0·5TiO₃-xSr_0.85Bi_0·1TiO₃, x = 0.5–0.7)], enabling the small size and weak correlation polar nanoregions (PNRs) with relatively high polarization. The trade-off was overcome by reducing the hysteresis of electrical switching of weak correlation PNRs. Thus, large recoverable energy storage density of 2.32 J/cm³ and high efficiency of 80.1% (250 kV/cm) were achieved simultaneously for x = 0.7 ceramics. Meanwhile, extremely rapid discharge rate (<30 ns) and remarkable power density of 63.7 MW/cm³, which were superior to the previously reported lead-free ceramics were realized. Besides, the 0.3BNT-0.7SBT ceramics also possess good thermal stability over 25 °C–115 °C at 100 kV/cm and good frequency stability (5–100 Hz). These properties make the 0.3BNT-0.7SBT ceramic an ideal candidate for energy storage applications.     

High permittivity and excellent high-temperature energy storage properties of X9R BaTiO3–(Bi0.5Na0.5)TiO3 ceramics

We fabricated x(Bi_0.5Na_0.5)TiO₃–(1−x)[BaTiO₃–(Bi_0.5Na_0.5)TiO₃–Nb] (BNT-doped BTBNT-Nb) dielectric materials with high permittivity and excellent high-temperature energy storage properties. The initial powder of Nb-modified BTBNT was first calcined and then modified with different stoichiometric ratios of (Bi_0.5Na_0.5)TiO₃ (BNT). Variable-temperature X-ray diffraction (XRD) results showed that the ceramics with a small amount of BNT doping consisted of coexisting tetragonal and pseudocubic phases, which transformed into the pseudocubic phase as the test temperature increased. The results of transmission electron microscopy (TEM) showed that the ceramic grain was the core-shell structure. The permittivity of the 5 mol% BNT-doped BTBNT-Nb ceramic reached up to 2343, meeting the X9R specification. The discharge energy densities of all samples were 1.70-1.91 J/cm³ at room temperature. The discharge energy densities of all samples fluctuated by only ±5% over the wide temperature range from 25°C to 175°C and ±8% from 25°C to 200°C. The discharge energy density of the 50 mol% BNT-doped BTBNT-Nb ceramic was 2.01 J/cm³ at 210 kV/cm and 175°C. The maximum energy efficiencies of all ceramics were up to ~91% at high temperatures and were much better than those at room temperature. The stable dielectric properties within a wide temperature window and excellent high-temperature energy storage properties of this BNT-doped BTBNT-Nb system make it promising to provide candidate materials for multilayer ceramic capacitor applications.     

Excellent thermal stability,high efficiency and high power density of (Sr0.7Ba0.3)5LaNb7Ti3O30–based tungsten bronze ceramics

A series of (1-x)(Sr_0.7Ba_0.3)₅LaNb₇Ti₃O₃₀–x(Bi_0.5Na_0.5)TiO₃ (x = 0.1–0.4) ceramics with tungsten bronze structure were prepared by solid state reaction. Phase composition, microstructure and energy storage properties were studied. When x = 0.3, excellent thermal stability satisfying the X7R specification was obtained and its energy storage as well as charge-discharge performances were further evaluated. Release energy density (W_re) of 0.77 J/cm³ and an energy storage efficiency of 97.3 % were detected at a low electric field of 20 kV/mm. Under the electric field of 10 kV/mm, the change of W_re in the temperature range of −55 °C to 125 °C is less than 15 % compared to room temperature. Short discharge period (∼0.17 μs), high power density (61.2 MW/cm³) and high discharge energy density (2.45 J/cm³) were evaluated by charge-discharge tests. Excellent thermal stability, high energy storage efficiency and high power density indicate that 0.7(Sr_0.7Ba_0.3)₅LaNb₇Ti₃O₃₀–0.3(Bi_0.5Na_0.5)TiO₃ ceramic is a promising pulse capacitor for working over a wide temperature range.     

Improved dielectric energy storage performance of Na0.5Bi0.5TiO3–Sr0.7Nd0.2TiO3 lead-free ceramics by adding an appropriate amount of AgNbO3

Based on the significant advantages of dielectric ceramics in high power energy storage, (1-x) (0.55Bi_0.5Na_0.5TiO₃-0.45Sr_0.7Nd_0.2TiO₃)-xAgNbO₃ (NBSNT-xAN) ceramics were prepared by traditional solid phase method. The introduction of AN in NBSNT ceramics not only increased the degree of relaxation, but also refined the grain size, enhanced the BDS, and finally improved the energy storage performance. It is found that the NBSNT-0.5AN ceramics obtained an effective energy storage density as high as 3.08 J/cm³ and an efficiency of 79.94%. In addition, good thermal stability and temperature stability were exhibited in the range of 30–120 °C and 10–350 Hz, and at the same time, it performed very well in the pulsed test at room temperature and variable temperatures. This provides a design idea for the miniaturization and integration of energy storage ceramic materials.     

Enhanced piezoelectric,electrocaloric and energy storage properties at high temperature in lead-free Bi0.5(Na1-xKx)0.5TiO3 ceramics

The piezoelectric, electrocaloric and energy storage properties were systemically investigated in lead-free Bi_0.5(Na_1-xK_x)_0.5TiO₃ ceramics from room temperature to high temperature region. These ceramics can be poled completely to obtain large piezoelectric coefficient (104–153 pC/N) at low electric field of ~30?kV/cm. The piezoelectric property shows good thermal stability due to high depolarization temperature (T_d). For BNKT₂₀, a large low electric field-induced strain of 0.36% is obtained at 120?°C under 50?kV/cm, the corresponding normalized strain coefficient is up to 720?pm/V, which is larger than other BNT-based ceramics at high temperature region. The electrocaloric properties of these ceramics are studied via indirect and direct methods. Large EC value (~1.08?K) in BNKT₂₀ ceramic is obtained at 50?kV/cm using indirect calculation. Above 100?°C, the dielectric energy storage density and efficiency of BNKT₂₀ is still up to ~0.85?J/cm³ and 0.75, respectively. The BNKT_x ceramics may become promising candidates in the fields of actuators, electrocaloric cooling and energy storage at high temperature region.     

Thermal-stability of electric field-induced strain and energy storage density in Nb-doped BNKT-ST piezoceramics

In this work, the relationship between the structural mechanisms and macroscopic electrical properties of the Nb-modified 0.96(Bi_0.5Na_0.84K_0.16TiO₃)–0.04SrTiO₃ (BNKT–ST) system were elucidated by using temperature dependent and in situ synchrotron X-ray diffraction (XRD) techniques. For the composition x?=?0.0175, a large-signal piezoelectric coefficient (S_max/E_max?=?d₃₃*) of 735 pm?V^?1 at 6?kV mm^?1 was observed at room temperature. Interestingly, at a higher temperature of 110?°C, the sample still showed a large d₃₃* of 570 pm V^?1. Furthermore, the temperature-invariant electrostrictive coefficient for this sample was found to be 0.0285?m⁴?C^?2 over the temperature range of 25–170?°C. Moreover, the energy density for x?=?0.030 sample was ～1.0?J?cm^?3 with an energy storage efficiency of ?70% in the temperature range of 25–135?°C. These results suggest that the synthesized Nb-modified BNKT–ST system is promising for the design of ceramic actuators as well as capacitor applications.     

Phase structure and electrical properties of lead free Na0·5Bi0·5TiO3–CaTiO3 ceramics

Abstract

Abstract

(1?x)Na_0·5Bi_0·5TiO_3?xCaTiO₃ ceramics with x?=?0–0·2 were prepared by solid state sintering method. Structural and morphology studies carried out by X-ray diffraction and scanning electron microscopy indicate the change in crystal structure from rhombohedral to orthorhombic symmetry (R3C to Pnma). The morphotropic phase boundary of this system was found to lie around x?=?0·08–0·14, where the orthorhombic and rhombohedral symmetries coexist. The orthorhombic phase is stabilised for x>0·14, indicating that the rhombohedral phase of Na_0·5Bi_0·5TiO₃ is susceptible to orthorhombic distortion brought about by Ca substitution. Calcium substitution in Na_0·5Bi_0·5TiO₃ caused an obvious decrease in peak temperature and a decrease in relative permittivity. The compositional variation of the fundamental dielectric behaviour is discussed in relation to the crystal chemistry of the system. The highest piezoelectric constant d₃₃ of 85 pC N^?1 is achieved for x?=?0·1, with the coercive field of 18 kV cm^?1 and the dielectric maximum temperature of 148°C.     

Simultaneously optimizing both energy storage density and efficiency in a novel lead-free relaxor antiferroelectrics

Dielectric capacitors with both high energy density and efficiency are highly demanded in pulsed power systems. Relaxor antiferroelectrics have attracted much attention due to their unique advantages in optimizing both properties of a dielectric capacitor. In this work, a novel relaxor antiferroelectric ceramic with composition of (1-x)Bi_0.5Na_0.5TiO₃-xAg_0.91Sm_0.03NbO₃ was developed, where the antiferroelectricity was stabilized with the increase of Ag_0.91Sm_0.03NbO₃ counterpart. Moreover, the relaxor feature was also obviously improved, as a result of chemical and structural disorder introduced by hetero cations with different radii and valence states. As expected, a high recoverable energy density of 2.1 J/cm³ accompanied with efficiency of 83 % was simultaneously achieved at x = 0.15. The as-prepared ceramics also exhibited good thermal stability in energy storage performance with small variations (energy storage density <10 % and efficiency <5 %) over 30−130 °C. All these merits demonstrate that the 0.85Bi_0.5Na_0.5TiO₃-0.15Ag_0.91Sm_0.03NbO₃ ceramic has great potential for high power energy storage applications.     

Temperature‐stable dielectric and energy storage properties of La(Ti0.5Mg0.5)O3‐doped (Bi0.5Na0.5)TiO3‐(Sr0.7Bi0.2)TiO3 lead‐free ceramics

A new type of (0.7?x)Bi_0.5Na_0.5TiO₃‐0.3Sr_0.7Bi_0.2TiO₃‐xLaTi_0.5Mg_0.5O₃ (LTM1000x, x = 0.0, 0.005, 0.01, 0.03, 0.05 wt%) lead‐free energy storage ceramic material was prepared by a combining ternary perovskite compounds, and the phase transition, dielectric, and energy storage characteristics were analyzed. It was found that the ceramic materials can achieve a stable dielectric property with a large dielectric constant in a wide temperature range with proper doping. The dielectric constant was stable at 2170 ± 15% in the temperature range of 35‐363°C at LTM05. In addition, the storage energy density was greatly improved to 1.32 J/cm³ with a high‐energy storage efficiency of 75% at the composition. More importantly, the energy storage density exhibited good temperature stability in the measurement range, which was maintained within 5% in the temperature range of 30‐110°C. Particularly, LTM05 show excellent fatigue resistance within 10⁶ fatigue cycles. The results show that the ceramic material is a promising material for temperature‐stable energy storage.     

Structural and thermoelectric properties of hydrothermal-processed Ag-doped Fe2O3

Fe_2-xAg_xO₃ (0?≤?x?≤?0.04) nanopowders with various Ag contents were synthesized at different hydrothermal reaction temperatures (150?°C and 180?°C). Their structural properties were fully investigated through an X-ray diffraction, a Fourier transform infrared spectroscopy, and an X-ray photoelectron spectroscopy. The hydrothermal reaction temperature, time, and Ag content remarkably affected the morphological characteristics and crystal structure of the synthesized powders. The Fe_2-xAg_xO₃ (0?≤?x?≤?0.04) powders synthesized at 150?°C for 6?h and the Fe_2-xAg_xO₃ (0.02?≤?x?≤?0.04) powders synthesized at 180?°C for 12?h formed the orthorhombic α-FeOOH phase with a rod-like morphology, whereas the Fe_2-xAg_xO₃ (0?≤?x?≤?0.01) powders synthesized at 180?°C for 12?h formed the rhombohedral α-Fe₂O₃ phase with a spherical-like morphology. The Fe_1.98Ag_0.02O₃ fabricated by utilizing Fe_1.98Ag_0.02O₃ powders synthesized at 180?°C showed the largest power factor (0.64?×10^?5 Wm^?1 K^?2) and dimensionless figure-of-merit (0.0036) at 800?°C.     

Tailoring structural and electrical properties of A-site non-stoichiometric Na0.5Bi0.5TiO3 ceramic at different sintering temperature

Na/Bi stoichiometry plays crucial role in determining various properties of sodium bismuth titanate-based system. In this work, we have synthesised lead free (Na_0.5Bi_0.5)_1+x TiO₃ (x?=?0, 0.02 and 0.05) ceramics by sol-gel method and systematically presented structural, dielectric and ferroelectric properties at different sintering temperature. Single phase perovskite structure with rhombohedral symmetry (R3c) is obtained for all compositions from low (850°C) to maximum (1150°C) sintering temperature. The shifting of x-ray diffraction peaks and characteristic perovskite metal-oxide vibrational band (～627?cm^?1) in Fourier Transform Infra-red spectra suggests compression or expansion of crystal lattice with Na/Bi non-stoichiometry. Excess of Na/Bi comprises dense crystal growth as compared to pure Na_0.5Bi_0.5TiO₃ composition suggesting compensation of volatile elements loss during heat treatment whose impact has also been observed in dielectric as well as ferroelectric properties. It is observed that Na_0.51Bi_0.51TiO₃ sample with x?=?0.02 exhibits better structural, dielectric and ferroelectric properties in whole range of sintering temperature.     

Temperature-stable dielectric ceramics based on Na0.5Bi0.5TiO3

Multiple ion substitutions to Na_0.5Bi_0.5TiO₃ give rise to favourable dielectric properties over the technologically important temperature range ?55?°C to 300?°C. A relative permittivity, ε_r,?=?1300?±?15% was recorded, with low loss tangent, tanδ?≤?0.025, for temperatures from 310?°C to 0?°C, tanδ increasing to 0.05 at ?55?°C (1?kHz) in the targeted solid solution (1–x)[0.85Na_0.5Bi_0.5TiO₃–0.15Ba_0.8Ca_0.2Ti_1-yZr_yO₃]–xNaNbO₃: x?=?0.3, y?=?0.2. The ε_r-T plots for NaNbO₃ contents x?<?0.2 exhibited a frequency-dependent inflection below the temperature of a broad dielectric peak. Higher levels of niobate substitution resulted in a single peak with frequency dispersion, typical of a normal relaxor ferroelectric. Experimental trends in properties suggest that the dielectric inflection is the true relaxor dielectric peak and appears as an inflection due to overlap with an independent broad dielectric peak. Process-related cation and oxygen vacancies and their possible contributions to dielectric properties are discussed.     

Enhanced energy-storage properties of (1-x)(0.7Bi0.5Na0.5TiO3-0.3Bi0.2Sr0.7TiO3)-xNaNbO3 lead-free ceramics

A series of (1-x)(0.7Bi_0.5Na_0.5TiO₃-0.3Bi_0.2Sr_0.7TiO₃)-xNaNbO₃ (BNT-BST-100xNN) lead-free ceramics were fabricated using conventional solid-state reaction technique. The phase behavior, microstructure, dielectric, ac impedance and energy-storage properties of the sintered ceramics were systematically investigated. XRD patterns and surface SEM micrographs revealed the introduction of NaNbO₃ didn't change the perovskite structure of BNT-BST at low doping level. The NaNbO₃ doping gave rise to slimmer P-E loops and thus gained enhanced energy storage properties. Therefore, a maximum energy storage density of 1.03 J/cm³ was achieved at 85 kV/cm at x = 0.01 via increasing the dielectric breakdown strength (DBS). Temperature-dependent dielectric permittivity illustrated the enhanced relaxor characteristics, implying the long-rang ferroelectric order was further damaged due to the introduction of NaNbO₃. The results above indicate the sintered ternary ceramics can be a promising lead-free candidate for energy storage capacitors.     

Superior temperature‐stable dielectrics for MLCCs based on Bi0.5Na0.5TiO3‐NaNbO3 system modified by CaZrO3

An ultra‐wide temperature stable ceramic system based on (1?x) [0.94(0.75Bi_0.5Na_0.5TiO₃?0.25NaNbO₃)?0.06BaTiO₃]?xCaZrO₃ (CZ100x) is developed for capacitor application in this study. All samples exhibit characteristics of pseudocubic structures in XRD patterns. With CaZrO₃ addition, the coupling effect of polar nanoregions (PNRs) is weakening, leading to greatly improved temperature stability of dielectric properties. Among all samples, the most attractive properties are obtained in the composition of CZ10 at <15% variation in dielectric permittivity spanning from ?55°C to 400°C and lower than 0.02 of dielectric loss of between ?60°C and 300°C, accompanied by high DC resistivity (10⁷ Ω m at 300°C, calculated by fitting Jonscher's power law). Furthermore, tentative multilayer ceramic capacitors (MLCCs) composed of CZ10 dielectric and Ag:Pd (70:30) internal electrode layers were fabricated by tape casting and cofiring processes. Temperature‐stable dielectric property in formation of MLCC was successfully realized, with small ΔC/C_25°C (<15%) and loss factor (≤ 0.02) between ?55°C and 340°C. Meanwhile, CZ10‐based MLCC showed temperature‐insensitive energy storage density of 0.31?0.35 J/cm³ and high‐energy efficiency of above 77% at 120 kV/cm in the range of ?55 to 175°C. All of these exhibit wonderful temperature‐stable dielectric properties and indicate the promising future of CZ10 dielectric as high‐temperature ceramic capacitors.     

Enhanced energy storage in temperature stable Bi0.5Na0.5TiO3-modified BaTiO3-Bi(Zn2/3Nb1/3)O3 ceramics

Recently, BaTiO₃-BiMeO₃ ceramics have garnered focused research attention due to their outstanding performance, such as thermal stability, energy efficiency and rapid charge-discharge behavior, however, a lower recoverable energy storage density (W_rec) caused by a relatively low P_max (<30 μC/cm²) mainly hinders practical applications. Herein, the energy density and thermal stability are improved by adding a tertiary component, i.e., Bi_0.5Na_0.5TiO₃, into BaTiO₃-BiMeO₃, resulting in xBi_0.5Na_0.5TiO₃-modified 0.88BaTiO₃-0.12Bi(Zn_2/3Nb_1/3)O₃ ceramics, with x = 0, 0.1, 0.2, 0.3 and 0.4, with superior dielectric properties and eco-friendly impact. Incorporating Bi_0.5Na_0.5TiO₃ with a high saturation polarization and Curie temperature not only significantly enhances P_max of BaTiO₃-Bi(Zn_2/3Nb_1/3)O₃ but also improves Curie temperature of (1-x)[0.88BaTiO₃-0.12Bi(Zn_2/3Nb_1/3)O₃]-xBi_0.5Na_0.5TiO₃ system. Combined with complementary advantages, modified ceramics render a superior energy storage performance (ESP) with a high W_rec of 3.82 J/cm³, efficiency η of 94.4% and prominent temperature tolerance of 25–200 °C at x = 0.3. Moreover, this ceramic exhibit excellent pulse performance, realizing discharge energy storage density W_dis of 2.31 J/cm³ and t_0.9 of 244 ns. Overall, the proposed strategy effectively improved comprehensive properties of BaTiO₃-based ceramics, showing promise in next-generation pulse applications.     

High energy storage density and efficiency in nanostructured (Bi0.2Na0.2K0.2La0.2Sr0.2)TiO3 high-entropy ceramics

High-entropy ceramics (HECs) (Bi_0.2Na_0.2K_0.2La_0.2Sr_0.2)TiO₃ (BNKLST) with single-phase perovskite structure have been successfully prepared by a modified citrate acid method. In comparison to (Bi_0.5Na_0.5)TiO₃ (BNT) ceramics prepared by the same synthesis route, the BNKLST HECs exhibit dense nanostructures with grain sizes as small as 45 nm, which are suggested to be responsible for the significantly improved electric breakdown fields and reduced leakage currents in the ceramics, and they have much enhanced elastic modulus owing to the entropy-stabilized perovskite structure. The electrical and dielectric characterizations reveal that BNKLST has high electrical resistances and dielectric constants at elevated temperatures, and, in particular, a recoverable energy storage density of 0.959 J/cm³ can be achieved under an applied electric field of 180 kV/cm. Moreover, the energy storage efficiency in BNKLST can be maintained to be larger than 90% at 40–200°C. These excellent properties suggest that entropy-stabilized BNT-based ceramics are promising dielectrics for electrical energy storage applications.     

Realizing high comprehensive energy storage performances of BNT-based ceramics for application in pulse power capacitors

Lead-free ceramic capacitors play an important role in electrical energy storage devices because of their ultrafast charge/discharge rates and high power density. However, simultaneously obtaining large energy storage capability, high efficiency and superior temperature stability has been a huge challenge for practical applications of ceramic capacitors. Here, the relaxor ferroelectric (1-x)[0.8Bi_0.5Na_0.5TiO₃-0.2Ba(Zr_0.3Ti_0.7)O₃]-xSr_0.7La_0.2TiO₃ ((1-x)(BNT-BZT)-xSLT) ceramics are prepared through solid-state reaction method to obtain excellent comprehensive energy storage performances. Particularly, high recoverable energy density (W_rec ～ 2.6 J/cm³) as well as superior efficiency (η ～ 92.2 %) can be achieved simultaneously under 210 kV/cm with composition of x = 0.3. Meanwhile, the corresponding ceramic shows excellent temperature (20?140 °C), frequency (1?200 Hz) and cycle stabilities (10⁶ st). Additionally, the 0.7(BNT-BZT)-0.3SLT ceramic also displays high power density (P_D ～ 38.8 MW/cm³) and extremely short discharge time (τ_0.9 ～ 0.11 μs). Therefore, this study provides a useful guideline for designing novel BNT-based ceramics with superior comprehensive energy storage performances.     

High temperature stable dielectric properties and enhanced energy-storage performance of (1− x)(0.85Na0.5Bi0.5TiO3 − 0.15Ba0.8Ca0.2Ti0.8Zr0.2O3)− xK0.5Na0.5NbO3 lead-free ceramics

Novel high temperature ceramic capacitors (1??x)(Na_0.5Bi_0.5TiO₃ ??0.15Ba_0.8Ca_0.2Ti_0.8Zr_0.2O₃)??xK_0.5Na_0.5NbO₃ were synthesized in the solid-state reaction route. The influence of K_0.5Na_0.5NbO₃ modification on dielectric behavior, energy-storage properties, ac impedance and temperature stable dielectric performance were systematically investigated. The reduced grain size and enhanced relaxor properties are obtained with the addition of KNN. The content of x?=?0.1 exhibits a stable permittivity (~ 1630) and dielectric loss (<?0.05) over a relatively broad temperature range (66–230?°C). A variation in permittivity within ±?15% can be observed over a pretty wide temperature range of 66–450?°C. Beyond that, this ceramic shows enhanced energy-storage properties with the density (W_rec) of 0.52?J/cm³ and efficiency (η) of 80.3% at 110?kV/cm. The possible contributions of the grain and the grain boundary to the ceramic capacitance are discussed by the ac impedance spectroscopy.