Search

The (1-x)BaTiO3-xCuO ceramics (x = 0, 0.5, 1.0, 1.5 and 2.0 wt%) were prepared by the traditional solid-state reaction method. The influence of the distribution of Cu-rich phase on the microscopic morphology, dielectric and complex impedance of BaTiO3 was studied. All samples show tetragonal phase structure. The images of SEM and EDS show that different amounts of CuO result in diverse distribution of Cu element at the grain boundary. The Cu element is concentrated in the grain boundary in a continuous network structure for x = 1.0 wt% and x = 2.0 wt%. And the Cu elements are mainly distributed in the punctate structure at triple junction for x = 1.5 wt%. Due to the pinning effect of Cu-rich phase at the triple junction, the grain of the BaTiO3 is refined. Not only is it beneficial to increase the permittivity and reduce the dielectric loss, but also improve the frequency stability of the dielectric performance at low frequency. In addition, the impedance analysis shows that the resistance and activation energy of conductivity of (1-x)BaTiO3-xCuO ceramics depend on the synergistic effect of the grain size and Cu-rich phase at the grain boundary. The smaller grain and the more Cu-rich phase at grain boundary, the greater resistance and activation energy of conductivity.

For the urgent demand of environmental protection and energy conservation, it is of great significance to develop environmentally-friendly dielectric ceramics with outstanding characteristic of energy storage and quick charge discharge capacity. For this study, we applied a strategy to achieve the enhancement of energy storage performance in (Ca0.5Sr0.5)1-xMgxTiO3 (abbreviate as CSMTx, x = 0.005, 0.010, 0.020, 0.040) linear ceramics based on the introduction of Mg2+ ion. Scanning electron microscopy and complex impedance measurement reveal that Mg2+ ion doping can refine grain size and increase grain boundary density, which results in grain boundary barrier strengthening owing to high-resistance grain boundaries. As a result, the marvellous energy storage properties, including an ultrahigh recoverable energy density of 2.88 J/cm3 combined with a giant energy efficiency of 90% are concurrently obtained in (Ca0.5Sr0.5)0.99Mg0.01TiO3 ceramic at an enhanced breakdown field (460 kV/cm). Meanwhile, this composition ceramic also exhibits the superior stability of frequency (1–1000 Hz) and temperature (20–100 °C) with minimal variation. In addition, the actual performance of ceramic capacitors in operation can be evaluated via the pulsed charge-discharge process. Delightedly, the superfast discharge speed (t0.9 = 20.4 ns), large current density (CD) of 421.23 A/cm2 and ultrahigh power density (PD) of 25.27 MW/cm3, as well as prominent thermal stability (20–100 °C) are synchronously produced in the CSMT2 ceramic. These merits qualify the unleaded linear ceramic as a competitive candidate for high-power capacitor applications, which offers a practicable approach for exploration on high-performance dielectric materials.

The pulse discharge characterization of perovskite dielectric ceramics, which has confronted a barrier between research and application, has the problems of inconsistent test standards and lack of comparability. To mitigate this issue and further advance the application process, we suggest an extrinsic standard (for convenience of comparison) for energy dielectric ceramics of thickness (0.2 mm), electrode area (4 mm2) and operation voltage (2 kV). We report the pulse discharge performance parameters of three typical dielectric materials: relaxor ferroelectric (Na0.5Bi0.5)0.9Li0.1Ti0.9Ta0.1O3 (NBLTT), paraelectric Ca0.6Sr0.4TiO3 (CST) and linear dielectric K0.5Na0.5NbO3 (KNN) glass ceramics through computer simulation and fitting of pulse discharge curves based on the resistance-inductance-capacitor pulse discharge circuit. The NBLTT ceramics exhibited higher peak current (16 A under 100 kV/cm) and stability with minimal variation less than 15% from 20 to 150 °C during pulse discharge compared with linear dielectric and ferroelectric glass ceramics. In addition, the NBLTT system holds the fast discharge time (90% of the discharge energy density released in about 100 ns) and good fatigue resistance. The short discharge time, high thermal stability and low medium voltage (500–5000 V) make the NBLTT ceramics promising for pulse capacitor in large current and low electric operation voltage conditions. An operable comparison standard and the research frontiers of pulsed dielectric materials are prospected.

The relationship between enhanced dielectric property and structural distortion in tungsten bronze structure ceramics was discussed in this work. The ceramics with the composition of (Ba1-xCax)2NaNb5O15 (x = 0, 0.1, 0.2, 0.3, 0.4) were fabricated via conventional solid-state method. All ceramics were pure without secondary phase and the distinct lattice distortion in structure was testified by Rietveld XRD refinement. Compared with the un-doped composition, the maximum polarization and energy storage density were strongly enhanced according to the ferroelectric property measurements, which were contributed to the distortion of NbO6 octahedron induced by the variation of ionic radius. The actually pulsed charge-discharge property of x = 0.3 ceramic was tested, whist excellent power density (PD = 35.106 MV/cm3) and discharge energy density (Wd = 0.29 J/cm3) were obtained at 100 °C under 120 kV/cm, revealing the potential for application of Ba2NaNb5O15 system-based ceramics in harsh environment.

Colossal permittivity (CP) ceramics have a great potential in the development of miniaturization, integration and lightweight of electronic components. In this work, NdxSr1-xTiO3 (0.000 ≤ x ≤ 0.014) (NST) ceramics are successfully prepared via sintering in N2. Simultaneously microstructure and dielectric properties of NST ceramics are characterized. It can be found that 0.010 ≤ x ≤ 0.014 ceramics show CP (>20000, 20–1 × 106 Hz) and low dielectric loss ( T i T i ' , N d S r ⋅ , V O ⋅ ⋅ ) forms the defect dipoles ( Ti Ti ' − N d S r ⋅ , T i T i ' − V O ⋅ ⋅ − T i T i ' ) and the defect clusters ( V O ⋅ ⋅ − 3 T i T i ' − N d S r ⋅ ), which produces the electron pinning effect and restricts the long-range movement of the carriers. Additionally, the grain boundary with high insulation resistivity plays a major role in the resistance of ceramics, and it also acts as a high barrier layer to limit the movement of several delocalized carriers.

High performance colossal permittivity (CP) ceramic materials are indispensable for the development of electronic devices. In this work, excellent Sr1-xDyxTiO3 (0.000 ≤ x ≤ 0.018) ceramic samples were prepared through a traditional solid phase method. It can be found that the insulation resistivity of 4.7 × 107 Ω/cm3 (DC 100V), the CP of 26712 and the low dielectric loss of 0.0065 (1 kHz) are obtained in x = 0.008 ceramic samples sintered in N2. Based on the analysis of XRD, XPS and comparison of sintering in different atmospheres, the excellent dielectric property is mainly determined by defect dipoles associated with oxygen vacancy (eg. Ti Ti ' − V O ⋅ ⋅ − Ti Ti ' ). These defect dipoles limit the long-range transition of electrons and result in electronic pinning effect. Additionally, it can be perceived that the insulation resistivity of 1.12 × 109 Ω/cm3 (DC 100 V), the CP of 23134 and the low dielectric loss of 0.0098 (1 kHz) are achieved in x = 0.008 ceramic samples after reoxidation. According to the analysis of complex impedance spectroscopy, the improvement of the insulation resistivity of x = 0.008 ceramic samples is mainly attributed to the increase of the grain boundary resistance.

The high energy density and power density dielectric ceramics with wide frequency and temperature stability are competitive materials for pulse power capacitors. This research proposes an effective strategy for enhancing energy storage performance of Ca0.5Sr0.5TiO3 ceramics through the introduction of Sn4+ ion. This ion restrains grain growth, increases high insulating grain boundaries, and thus enhances the barrier height of grain boundaries, which are demonstrated in SEM micrographs and complex impedance. The Ca0.5Sr0.5Ti0.97Sn0.03O3 (SnCST3) ceramics possess high energy storage density of 2.06 J/cm3 and efficiency of 95% under breakdown strength of 330 kV/cm, which get benefit from wide band gap of 5.3 eV. While the exceptional stability with minimal fluctuation (

The present work investigates the influence of donor doping and its concentration on the flash sintering behavior of barium titanate. The characteristic of non-ohimic conductivity during flash event shows that flash sintering is associated with dielectric breakdown due to the similar physical phenomena. The polarization of dielectric particle contributes to the enhancement of local electric field strength. The magnified electric field caused by local charges accumulation gives rise to dielectric breakdown phenomenon during flash sintering. The SEM measurement indicates an obvious breakdown channel through the inside of sample, which provides a convincible evidence for dielectric breakdown. In addition, the impacts of temperature and field on carrier activation and migration are emphasized. Eventually, the non-ohmic conductivity can be explained by the physical phenomenon of dielectric breakdown described by Poole-Frenkel Emission.

A series of high entropy Ba(Zr0.2Ti0.2Sn0.2Hf0.2Me0.2)O3 (Me=Y3+,Nb5+,Ta5+,V5+,Mo6+,W6+) perovskite oxides were synthesized by using a solid state reaction method. Three multiple-cation solid solutions formed pure phase compounds, and only two compounds were sintered into ceramics. Microstructure analysis showed the influence of configurational entropy on phase stability and grain growth. Dielectric measurements showed that the high entropy ceramics possessed decent temperature stability of permittivity from 25 °C to 200 °C, low dielectric loss (

SrBi2Nb1.8−xCoxFe0.2O9 (SBCFN, x = 0, 0.1, 0.2, 0.3 and 0.4) ceramic samples were fabricated by traditional solid-state reaction. Structure was detected by XRD and SEM, which demonstrated that all samples showed pure orthorhombic Aurivillius structure and the plate-like grains were observed. The morphology gradually disappeared with Co ions doping. Relaxation peak in low-temperature region of Co-doped samples was discussed in dielectric spectra. Besides, the decrease in resistance induced by the motion of first ionized oxygen vacancies was revealed by fitted Arrhenius curves and supported by Correlated Barrier Hopping conduction model. The contribution of leakage current in P–E loops was observed. The optimum magnetic property was obtained when the molar ratio of Fe3+ and Co3+ is 1:1, which is attributed to introduction of double exchange interaction (Fe–O–Co). At the same time, the Eg was narrowed due to hybridization and lattice distortion, which was coincident with the result of resistance.

Multiferroic Bi5−xYxTi3FeO15 (BYTF-x, x = 0, 0.1, 0.3, 0.5, 0.7) ceramics were synthesized through the conventional solid-state reaction. The structure, dielectric, multiferroic and magnetodielectric properties of BYTF-x were investigated in detail. X-ray diffraction confirmed that all the samples were layered Aurivillius structure. Upon increasing Y content, the grain size of samples slightly decreases. The dielectric permittivity increased with Y doped. The Y doping has no effect on microstructural changes of plate-like grains which verified though field-emission scanning electron microscopy. The minimum remanent polarization (2Pr = 2.48 μc/cm2) was observed in BYTF-0.3 ceramic and the maximum magnetodielectric coefficient value of 1.23% was obtained in BYTF-0.3 ceramic perhaps result from the coexistence of Fe2+ and Fe3+. Additionally, weak ferromagnetic is only found in BYTF-0.3 ceramic. The ferromagnetism can be attributed to ferromagnetic double exchange interactions (Fe2+–O–Fe3+) and the spin canting of tilting FeO6 octahedra via the Dzyaloshinskii–Moriya interaction. These results indicate that Y doping Aurivillius phase may be the potential candidates for exploring superior room-temperature multiferroics.

A novel (1-x)Na0.5Bi0.5TiO3-xBaHfO3 (abbreviated as (1-x)NBT-xBH) transparent ceramic was fabricated by the solid state reaction method. X-ray diffraction analysis showed that NBT-based transparent ceramics exhibit a cubic-like perovskite structure and the solid solubility of BH in NBT reached to 0.15. The Landau-Devonshire theory and I-E curves revealed that the transition between the antiferroelectric like phase and the ferroelectric phase deeply relies on the variation of composition and free energy. One sample (x = 0.15) was found to show a high dielectric constant (˜2418±10%) over the temperature range 57–400 °C. These ceramics also exhibited a high discharge energy density (Wd) of 2.1 J/cm3 and a high maximum polarization Pm of 34 μC/cm2 under relatively low electric fields which were less than 175 kV/cm. There was also high transparency in the visible spectra (more than 0.5) when the sample thickness was 250 μm.

The magnetoelectric composites of (1-x)BaTiO3-xSr2CoMoO6 (x=0.02, 0.04, 0.06, 0.08, 0.10 and 0.12) are synthesized successfully via solid state reaction. The dielectric, multiferroic and magnetodielectric properties were discussed in details. The XRD data confirm the single perovskite phase among the composites. In addition, as the content of Sr2CoMoO6 increase, the diffraction peaks shift to higher angle which indicates the gradually decreased lattice parameters. The observed dielectric relaxation phenomenon could be attributed to Maxwell-Wagner (MW) model. The weak ferromagnetism was observed for x=0.02, 0.04 with the remnant magnetization (Mr) 0.025 memu/g, 0.065 memu/g and coercivity (Hc) 4 Oe, 10 Oe, respectively despite the anti-ferromagnetic nature of Sr2CoMoO6. Furthermore, the M − H hysteresis loops of (1-x)BaTiO3-xSr2CoMoO6 change obviously with polarization state, which is related to the ordering degree of the Co and Mo sites. The reason for observed magnetodielectric effect is the influence of magnetoresistance (MR) on Maxwell-Wagner (MW) effect.

The application of numerous colossal permittivity (CP, > 103) materials was limited on account of relatively higher dielectric loss (>0.05). In this work, the xwt% B2O3 (x = 0, 0.5, 1, 2, 4) adding Ti0.99(Eu0.5Nb0.5)0.01O2 (TENO-xwt% B2O3) ceramics were prepared by a traditional solid state method. SEM analysis indicated that the average grain sizes obviously decreased by adding B2O3 and the low dielectric loss corresponding with the colossal permittivity were obtained in all samples. Especially, the higher permittivity of 4.1 × 104 and lower dielectric loss of 0.012 were achieved while x = 2 at 1 kHz and room temperature respectively, accompanying with good temperature stability ranging from −55 °C to 200 °C. Moreover, the formation mechanism of excellent dielectric properties was studied on the basis of analysis of the SEM, complex impedance and electric modulus. The results showed that the addition of B2O3 refined the grains and strengthened the interface effect. Furthermore, the B2O3 existing in the grain boundary formed barrier layer which hindered the long range motion of electrons.

(Ca0.5Sr0.5)1-1.5xLaxTiO3 (x = 0.000, 0.050, 0.075, 0.100, 0.150) ceramics were successively fabricated by conventional solid state method. Structure characterization were detected by XRD and SEM, demonstrating the influence of La2O3 doping on the microstructure. In addition, this effect on relaxor behavior corresponding to resistivity of grain boundary was discussed by dielectric and impendance spectra. The determining band gap energy (Eg) was estimated by Ultraviolet–Visible Spectrophotometry in order to investigate the effect of band gap on the breakdown strength. The dielectric breakdown strength was found to significantly enhanced on the basis of Ca0.5Sr0.5TiO3 ceramics with La2O3 doping, the (Ca0.5Sr0.5)0.8875La0.075TiO3 samples possessed widest band gap (∼5.2 eV) and exhibited maximum breakdown strength of 370 kV/cm corresponding with a large recoverable energy storage density of 2.07 J/cm3. Furthermore, the excellent stability of energy storage properties and ultrahigh energy efficiency of above 93% at wide frequency (1–1000 Hz) as well as high temperature (20–180 °C) was obtained for (Ca0.5Sr0.5)0.8875La0.075TiO3 ceramics, which reveal samples as good candidate for linear energy storage fileds.

To further manipulate the dielectric properties of (Na0.5Bi0.5)0.775Ba0.225Ti0.775Sn0.225O3 ceramics, (Na0.5Bi0.5)0.775Ba0.225Ti0.775Sn0.225O3 − x wt% Bi2O3–B2O3–ZnO (BBZ) ceramics were prepared via a conventional solid state reaction method, whilst the effect of BBZ glass content on dielectric and ferroelectric properties was investigated. In XRD patterns, the minimal secondary phase of Zn3(BO3)2 can be detected in these compounds when x > 5. With the addition of BBZ glass, diffuse phase transition behavior (DPT) and the high temperature stability of permittivity were enhanced. When x = 7, a high permittivity of 1600 ± 15%, from ~ 50 to ~ 475 °C was obtained. Additionally, a high Wd of 1.4 J/cm3 and 𝜂 of 75.5% (measured at 150 kV/cm) were achieved due to the enhanced Pm of 24 μC/cm2. This work demonstrated that the study on (Na0.5Bi0.5)0.775Ba0.225Ti0.775Sn0.225O3 ceramics with BBZ glass addition providing an adequate strategy to enhance Pm.

Single-Phase Aurivillius SrBi3Nb2FeO12 ceramics were prepared by conventional solid-state method. BiFeO3 was successfully introduced into SrBi2Nb2O9 which was confirmed by XRD and Raman results. Plate-like morphology grains which are 400–600 nm in thickness and 2–4 µm in length were observed for SrBi3Nb2FeO12 ceramics. Their permittivity and dielectric loss at 1 MHz are about 135 and 0.018, respectively. Two permittivity peaks were observed in the temperature dependent permittivity curves. Ferroelectric and weak antiferromagnetic properties were obtained simultaneously at room temperature. X-ray photoelectron spectroscopy (XPS) was carried out to investigate the chemical state of SBNF and Fe ion was found in mixed state. These results indicate that three-layered SrBi3Nb2FeO12 ceramics can be used as a kind of multiferroics in further research.

Dense (1-x)(0.775NBT-0.225BSN)-xBZ ternary ceramics were fabricated by solid state methods and their dielectric and ferroelectric properties were systematically investigated. XRD and Raman analysis indicate that the structure complexity and phase diffusion were enhanced in 0.775NBT-0.225BSN relaxor system with BZ addition. With increasing the contents of BZ, average grain size greatly decreases. Dielectric study shows that dispersive relaxor-like behavior was beginning to convert to diffusive phase transition when x ≥ 0.2. Along with increasing the BZ contents, the slop of P-E loops and the energy-loss can gradually decrease. When x = 0.2, both a high Wd of 2.08 J/cm3 and η of 88.8% were achieved, due to the slimer P-E loops, the high Pm (∼20 μC/cm2) and Eb (245 kV/cm). As a result, the ternary ceramics system may be a good candidate for energy-storage ceramics of NBT-based materials.

The Bi0.95-xLa0.05YxFe0.95Ti0.05O3 (BYFO) (x = 0, 0.04, 0.06, 0.08, 0.10) ceramics were synthesized by traditional solid phase method. The samples for BYFO ceramics were tested for X-ray diffraction (XRD) techniques, magnetic hysteresis (M–H)loops, scanning electron microscope (SEM). The leakage current were weakened because highly dense microstructure and low porosity ceramics were compounded. When x = 0.06, remanent polarization (Pr) is 0.3079 μC/cm2, and saturization polarization (Ps) is 1.3542 μC/cm2 for BYFO ceramics. Saturation magnetization (Ms) and remanent magnetization (Mr) are increased to 1.91926 emu/g, 1.43179 emu/g respectively. The obtained values of the magnetodielectric coefficient (αMD) comes to maximum value, which is 15.64% for x = 0.08.

Dielectric materials with high energy densities and efficiencies are greatly required in the field of power electronics to satisfy demand. This study presents a regulating strategy through Zr4+ doping and oxygen treatment for reliably enhancing the energy storage performances of Ca0.5Sr0.5TiO3 ceramics. The introduction of Zr4+ inhibits grain growth, and grain boundary barrier effects are enhanced via oxygen treatment; these outcomes are systemically analyzed using complex impedance data. Exceptional energy storage performance is shown; an energy density of 3.37 J cm−3 and 96% energy efficiency under a breakdown strength of 440 kV cm−1 are obtained simultaneously in Ca0.5Sr0.5Ti0.85Zr0.15O3 ceramics following oxygen treatment, which are better results than for other reported linear dielectric systems. This system also possesses excellent stability, with minimal fluctuations (

Dielectric capacitors with fast charge–discharge rate and high power density are drawing more attention in pulse power equipment field. In this work, bismuth-based high entropy compound (HEC), Bi(Zn0.2Mg0.2Al0.2Sn0.2Zr0.2)O3 (BZMASZ), was introduced into BaTiO3-Na0.5Bi0.5TiO3 (BT-NBT) matrix, in order to improve the comprehensive energy storage performance. The addition of BZMASZ induced phase transition from tetragonal phase to cubic phase, along with the enhancement of relaxor behavior and local nanodomains. The 0.1 BZMASZ modified 0.75BT-0.25NBT ceramics exhibited excellent recoverable energy density of Wrec ~ 3.74 J/cm3, high conversion efficiency of η ~ 82.2 % and superior temperature stability of ± 4.5 % from −30 to 200 °C. Combined with the high power density of PD ~ 34.76 MW/cm3 and rapid discharge rate of t0.9 ~ 67 ns, the x = 0.1 ceramics are considered to be the promising candidate for future wide-temperature pulse power applications.

0.55BNT-0.45BCTZS-x wt% MgO ceramics were sintered by microwave sintering method. XRD data shows that the reaction between MgO and the matrix phase was suppressed and the secondary phase of MgO was observed in MgO doped samples. SEM and EDS mapping results prove that all samples exhibit a dense microstructure and MgO mainly aggregates at grain boundaries. Dielectric properties indicate that the relaxor behavior can be enhanced by MgO addittives, while x = 3–7 samples show a diffuse phase transition characteristic. The maximum polarization of the samples prepared by microwave sintering is higher than that of the samples prepared by traditional sintering. A high energy storage density of 2.09 J/cm3 and the breakdown strength of 18.97 kV/mm were obtained in the x = 5 sample, of which the energy efficiency was 79.51%.

Aurivillius phase SrBi 2 Nb 2- x Fe x O 9 ( x = 0, 0.1, 0.2, 0.3, 0.4 and 1) ceramics prepared by conventional solid-state method. The introduction of Fe does not change the layered perovskite structure of SrBi 2 Nb 2 O 9 . Upon increasing Fe content, the T m of the samples shifts from 437 °C ( x = 0) to 524 °C ( x = 0.4) due to lattice effect. Temperature dependence of dielectric permittivity described according to modified Curie-Weiss law. When reaching up x = 0.4, the diffuseness of the dielectric peak becomes more pronounced. The minimum value of P r and E c obtained when x = 0.3 because of Fe 3+ weakens Nb-O hybridization and more oxygen vacancies appeared in samples. The antiferromagnetic properties arise for the samples is explained by super exchange interaction (Fe 3+ -O-Fe 3+ ).

A novel system of lead-free dielectric temperature stability materials BaFe0.05Nb0.05Ti0.9O3-Bi0.5Na0.5TiO3-xBiMg2/3Nb1/3O3 are fabricated via a conventional solid state reaction method. The concerted mechanism on the dielectric properties of different proportion of BMN additive in BaFe0.05Nb0.05Ti0.9O3-based ceramics is investigated systematically. The phase transition, and dielectric properties have been obtained by X-ray diffraction and dielectric measurements as a function of chemical composition and temperature. Microstructure and crystal structure are investigated, and electrical responses are observed in the combined modulus and impedance plots. With increasing the BMN non-ferroelectric phase, core-shell structure disappeares, temperature-stable dielectric properties over a wide temperature range. The x = 0.2 ceramic shows the optimal dielectric performance, has TCC values of ± 15% from −55 to 450 °C, with permittivity value at room temperature is 605. The good TCC demonstrates that the BFNT-BNT-xBMN system would have a promising future in application as ultra-broad working temperature and high frequency dielectrics.

The effects of KNbO3 addition on the temperature stability of dielectric properties and energy-storage performances of Sr 0.5Na0.25Bi0.25TiO3-MgO ((1-x)SNBTM5-xKN) ceramics were systematically investigated. It shows that KNbO3 has completely diffused into SNBT lattice to form a solid solutions. Two obvious maxima in permittivity curves were observed due to the formation of the polar nanoregions. For the sample with x = 0.05 addition, its permittivity variation region, where △e'/e'25 °C is no more than ± 15%, retains wide the range from −55 °C to 200 °C, indicating that the ceramics can meet the requirement of X9R specification. Furthermore, this sample shows a high electric breakdown strength of 17.85 kV/mm and a high discharge energy density of 2 J/cm3. The noticeable reduced remnant polarization induced by KNbO3 addition also contributes to the improved energy-storage performances. Thus, these novel ceramics with the aforementioned characteristics will potentially benefit the applications of high pulse power capacitors at high temperatures.

The sensitivity toward mechanical stress of barium titanate-based positive temperature coefficient resistor material was investigated by determining the resistance change with application of uniaxial stress from room temperature to 200 °C, which is well above the Curie temperature TC. Using the Landau–Ginsburg–Devonshire theory the resistance increases in the paraelectric state, the negligible impact of stress close to TC and the observed increase in TC with increasing stress could be rationalized. For the ferroelectric state, the stress-related resistance increase was attributed to ferroelasticity, a change in bulk permittivity and interfacial stress inducing a piezoelectric potential. The obtained results are also discussed with respect to recent endeavors to tune properties of potential barriers in piezoelectric semiconductors by mechanical stress.

Phase constitution, microstructure, dielectric performance, polarization, breakdown strength as well as energy storage behaviors for the (1 − x)(0.45SrTiO3–0.2Na0.5Bi0.5TiO3–0.35BaTiO3)–xSnO2 (STNBTBT–Snx) were systematically investigated. The dielectric measurements exhibit a relaxor behavior, and the dielectric loss is very low (

lead-free (0.8-x)SrTiO3-0.2Na0.5Bi0.5TiO3-xBaTiO3 ceramics (abbreviated as (0.8-x)ST-0.2NBT-xBT) were prepared by the conventional solid-state sintering method, and their crystal structure, dielectric properties, relaxor behavior and energy-storage property were investigated as a function of BT concentration. X-ray diffraction results reveal a pure perovskite structure with a pseudo-cubic phase. The dielectric measurements exhibit a relaxor behavior for all samples and the Tm gradually increases (from −49.67 °C to 67.91 °C) with increasing x. The pinched polarization-electric field (P-E) loops were observed in the samples with x ≤ 0.40 and the maximum polarization (Pm) increased from 11.37 μC/cm2 to 20.79 μC/cm2 at 8 kV/mm while x = 0.20–0.55. The maximum discharge energy-storage density (Jd) (1.78 J/cm3) is obtained in x = 0.35 ceramic with a relatively high Pm (29.19 μC/cm2) under an electric field of 17 kV/mm, which makes (0.8-x)ST-0.2NBT-xBT ceramics may be promising lead-free materials in practical high energy storage application.

To decrease the dielectric loss over a broad temperature and frequency of Ba(Fe0.5Nb0.5)O3 (BFN) ceramics, the core-shell structure of Ba(Fe0.5Nb0.5)O3@SiO2 (BFN@SiO2) particles were successfully prepared by aqueous chemical coating approach, which still remains in the final ceramics. The mechanism of coating BFN with SiO2 is also analyzed. The BFN@SiO2 sample shows good frequency and temperature stability on dielectric constant and the dielectric loss is significantly decreased. The low tan δ is related to the homogeneous fine grains and the insulating grain boundaries of BFN@SiO2 ceramics. The improved temperature stability in BFN@SiO2 ceramics is a competing balance result of the low and high temperature dielectric relaxations. The enhancement resistance of grain boundaries plays a key role to reduce the dielectric loss of the BFN@SiO2 ceramics. The XPS analysis confirms the blocking function of insulating SiO2 shell on loss of the oxygen and matter transfer.

The investigation of the microstructure and electrical properties of lead-free (1 − x)(0.92BaTiO3–0.08K0.5Bi0.5TiO3)–xKNbO3 ceramics where x = 0, 0.005, 0.01, 0.02, 0.04, 0.06, 0.08 and 0.10 was carried out. (1 − x)BTKBT–xKN ceramics were prepared by conventional solid state reaction method. The XRD patterns revealed change in crystal symmetries from tetragonal to pseudocubic structure with increasing KN contents. In addition, dielectric constant and dielectric loss versus frequency were characterized in the frequency range from 1 kHz to 1 MHz. It is found that the dielectric constant and the dielectric loss changed with the increase of KN contents regularly. The Curie temperature of (1 − x)BTKBT–xKN composite is dependent on the KN content, which confirms the XRD results. Energy storage density and energy storage efficiency were calculated from polarization versus electric field hysteresis loops. Value of energy storage efficiency increased with the increase of KNbO3 content. A relatively large energy storage density of 0.89 J/cm3 was obtained in the x = 0.08 samples.

(1-x)NaNbO3-xLiTaO3 ceramics were synthesized by solid state reactions and the phase transition, dielectric and ferroelectric properties were studied. XRD and Raman results suggested that the anti-ferroelectric orthorhombic P phase (Pbma) gradually transformed into the ferroelectric orthorhombic Q phase (P21ma) when x ≥ 0.10, and the turning points of v1, v3 and v6 appeared when x = 0.15, which is probably due to the competition of two kinds of O phase with increasing x. The diffuse relaxor behavior of NN ceramics were obviously increased by LT addition, and the x = 0.10 sample possessed a comparable ΔTm with x = 0.05 samples. As a result, the x = 0.10 sample possesses a fast ferroelectric switching time of 1.75 ms and a high Pr of 27 μC/cm2, due to the enhanced ferroelectric phase and relaxor diffuse behavior. In addition, the x = 0.10 sample also shows a well rectangular P-E loops, indicating its potential applications in ferroelectric memory devices.

Ba(Fe0.5Ta0.5)O3/poly(vinylidene fluoride) (BFT/PVDF) flexible nanocomposite films are fabricated by tape casting using dopamine (DA)-modified BFT nanopowders and PVDF as a matrix polymer. After a surface modification of installing a DA layer with a thickness of 5 nm, the interfacial couple interaction between BFT and PVDF is enhanced, resulting in less hole defects at the interface. Then the dielectric constant (e′), loss tangent (tan δ), and AC conductivity of nanocomposite films are reduced. Meanwhile, the value of the reduced dielectric constant (Δe′) and the strength of interfacial polarization (k) are introduced to illustrate the effect of DA on the dielectric behavior of nanocomposite films. Δe′ can be used to calculate the magnitude of interfacial polarization, and the strength of the dielectric constant contributed by the interface can be expressed as k. Most importantly, the energy-storage density and energy-storage efficiency of nanocomposite films with a small BFT@DA filler content of 1 vol % ...

0.7Ba 0.9 Ca 0.1 TiO 3 −0.3Na 0.5 Bi 0.5 TiO 3 - x LiBa 2 Nb 5 O 15 ceramics were prepared by solid state route. X-ray diffraction results reveal that the phase structure of the samples gradually transform from tetragonal to pseudo-cubic symmetry with the increasing content of LiBa 2 Nb 5 O 15 . The investigation found that the moderate doping of LiBa 2 Nb 5 O 15 in 0.7Ba 0.9 Ca 0.1 TiO 3 −0.3Na 0.5 Bi 0.5 TiO 3 ceramic can decrease its phase transition temperature, broaden its dielectric peak and enhance its relaxor behavior. The dielectric temperature stability of 0.7Ba 0.9 Ca 0.1 TiO 3 -0.3Na 0.5 Bi 0.5 TiO 3 ceramic was improved effectively with the increasing content of LiBa 2 Nb 5 O 15 . It was found that the x =0.005 sample has an operational temperature range from 4.3 °C to 145.6 °C. The maximum polarization, remanent polarization and coercive electric field of the samples gradually decreased and the P - E hysteresis gradually became slim. The sample with x =0.006 show a maximum energy storage density of 1.06 J/cm 3 .

The Ba 0.4 Sr 0.6 TiO 3 (BST) ceramics with Bi 2 O 3 -B 2 O 3 -ZnO (BBZ) glass additive were prepared by the solid state reaction route. Microstructural observation demonstrates that the average grain size reduces obviously with increasing glass additive. The dielectric constant decreases and the dielectric breakdown strength (BDS) increases as glass additive increases. The energy storage density of ceramics with 5 wt% glass additive is 0.62 J/cm 3 attributed to the relatively high dielectric constant and BDS. These results indicate that this material is a promising candidate for energy storage capacitor devices.

Di-phase multiferroic composite ceramics of 0.9BaTiO3-0.1Ba(1-x)SrxFe12O19 have been successfully prepared using microwave hydrothermal and microwave sintering methods. The mobility is decreased resulting in increased resistivity due to the crystal structure becomes more compact (Sr2+ ionic radius is smaller than Ba2+) after doping Sr2+. The study of dielectric exhibits the tanδ decreasing and e′ increasing after doping Sr2+. To further study the two relaxation peaks, the activation energy is calculated which originate in the Debye-like relaxation and hopping of electrons between Fe2+/Fe3+, respectively. The P-E loops show slimmer loops as a result of reduced the dielectric loss and conductive leakage loss owing to higher resistivity obtained after doping Sr2+. All the magnetic hysteresis loops present a waisted shape which is attributed to the change of grain size and existence of non-magnetic phase BaTiO3. In summary, the nearly invariable ferromagnetism but enhanced dielectric and ferroelectric properties multiferroic composite ceramics are obtained by doping Sr2+. In addition, the sample of x = 0.6 has the best-integrated performance among all the contents.

Ba0.4Sr0.6TiO3 (BST) powders were prepared by hydrothermal method, the ceramics were sintered in N2, air and O2 atmosphere respectively. The effect of sintering atmosphere on the microstructure, dielectric properties, and energy storage performance of BST ceramics were investigated. The grain size of the BST ceramics sintered in O2 atmosphere was reduced to 0.44 µm, indicating the grain growth was significantly inhibited with increasing oxygen partial pressure due to the lack of oxygen vacancy. Dielectric relaxation behavior was observed in the BST ceramics, and the degree of which was increased with increasing oxygen partial pressure. BST ceramics sintered in O2 atmosphere showed the largest critical breakdown strength of 16.72 kV/mm, at which the highest energy storage density of 1.081 J/cm3 and a moderate energy storage efficiency of (73.78%) were obtained. The dependence of energy-storage properties on applied field was also investigated, it was found that the energy storage density increased with increasing applied filed while the energy storage efficiency decreased with increasing applied filed.

Multiferroic bismuth ferrite (BiFeO 3 , BFO) is one of the most promising high-temperature ferroelectric and piezoelectric materials due to a high Curie temperature ( T C ∼830 °C) if the enhancement of ferroelectricity and piezoelectricity can be realized. In this work, we introduced La ( x =0.05–0.30) to BFO to change its crystal structure and obtained an enhanced Rhombohedral structure. The high pure La x Bi (1− x ) FeO 3 (LBFO) powders with refined grain size were prepared by microwave hydrothermal method, then the ceramics were sintered under microwave condition. The enhanced piezoelectric property results (d 33 =55–62pC·N −1 ) showed that La 3+ could not only stable the Rhombohedral structure and form Metastable phase contributing to the piezoelectric effects at a special range of doping contents. The figure of dielectric property versus frequency indicated La 3+ doped BFO ceramics could increase dielectric constant and reduce the loss. The values of bulk resistance (R b ) obtained from the intercept of semicircular arcs on the real axis (Z) at different temperatures decrease with the increasing of the doping contents. The P r increased which could be ascribed to that the introduction of La could lead to the distortion of the crystal structure of BFO ceramics and the formation of more dipoles or short-range charge carriers. Finally, the M-H loops suggested that the Saturation magnetization and Coercive magnetic field LBFO ceramics was improved with increasing La contents.

The 0.92BaTiO3–0.08BiMO3 (M = Fe, Y, Al) solid solutions were prepared via a conventional solid state reaction technique. X-ray diffractometer, Raman spectra, scanning electron microscope, and impedance analyzer were used to examine the effect of three additions on the crystal structure, micromorphology and dielectric properties of 0.92BaTiO3–0.08BiMO3 (M = Fe, Y, Al) solid solutions. The 0.08 BiMO3 (M = Fe, Y, Al) additions totally transform the characteristic sharp phase transition (associated with permittivity maximum) of pure BaTiO3 into a less-distinct phase transition with a broad and strongly dispersive permittivity maximum characteristic of relaxor dielectrics.

(1-x)SrTiO3-x(Na0.5Bi0.5)TiO3 ((1-x)ST-xNBT) ceramics have been prepared by solid-state route and their structure, electric and energy storage properties have been investigated. Dielectric anomalies at Tm and T′m show strong frequency dispersion as the typical relaxor ferroelectrics behavior over a broad temperature range. The Tm of (1-x)ST-xNBT ceramics dramatically shifted to a higher temperature (from −118 °C to 106 °C at 1 kHz) with increasing x. All samples showed the broad relaxor behavior due to the increase in the degree of lattice disorder and the thermal evolution of PNRs, and exhibited a discharge energy density of more than 1.18 J/cm3. The x = 0.4 sample exhibited a maximum discharge energy density of 1.70 J/cm3, consistent with the high value of Eb (∼21 kV/mm) and Pm (∼25 μC/cm2). The results indicate that (1-x)ST-xNBT ceramics might be a promising environmental friendly material for energy storage application.

To develop dielectric materials with high dielectric constant and low dielectric loss, a novel three-phase composite was prepared by embedding the nano-sized Ba(Fe0.5Nb0.5)O3 (BFN) crystallites and Ni crystallites into poly(vinylidene fluoride) (PVDF) matrix. The structure, dielectric and electrical properties of the composites were investigated. The superiority of this method is that, when compared with the two-phase Ni/PVDF composites, three-phase composites not only show significantly increased dielectric constants but also have lower dielectric loss. Our results show that a high dielectric constant of 475 and a relatively low loss of 0.61 were achieved at 100 Hz with 25 vol.% Ni and 50 vol.% BFN, respectively. The enhancement of dielectric constant of polymer based composites can be interpreted by the mini-capacitor principle and the interfacial polarization. The relatively low dielectric loss could be attributed to the isolation effect of BFN fillers. These composites with high dielectric constant and low dielectric loss are found to be potentially useful for embedded capacitor applications.

Dopamine@(In 0.05 Nb 0.05 )Ti 0.9 O 2 /poly(vinylidene-fluoride) (DA@INTO/PVDF) composites are fabricated via a physical mixing method followed by heat treatment. TEM results show that DA is uniformly coated on the surface of INTO particles with a thickness of 10 nm. SEM results show that the DA@INTO particles are homogeneously dispersed in PVDF. Compared with INTO/PVDF composites, DA@INTO/PVDF composites exhibit excellent dielectric constant and energy discharge efficiency, which is due to the improved interfacial polarization and reduced leakage current. DA plays an important role in the enhanced dielectric properties of DA@INTO/PVDF composites.

The polycrystalline 0.94BaTiO 3 -0.06(Bi 0.5 Na 0.5 )TiO 3 -0.2Bi(Mg 0.5 Zr 0.5 )O 3 - x Ba(Fe 0.5 Nb 0.5 )O 3 (0.94BT-0.06BNT-0.2BMZ- x BFN) ( x = 0–0.125) ceramics are fabricated via a conventional solid state reaction method. A continuous progressive decline in e rmax with increasing x leads to near temperature-stable dielectric properties over a wide temperature range. It was demonstrated that the dielectric temperature stability of BT based ceramics can be improved effectively with increasing x . Stability in values of relative permittivity over a wide temperature range was demonstrated for x = 0.1, with e r = 850 ± 15% over the temperature range ≤−45.01–250.15 °C, and tanδ ≤ 0.02 from 37 °C to 120 °C.

Fine-grained BaTiO3 ceramics with different grain sizes (96–194 nm) were prepared by microwave sintering, and the grain size (GS) effect of fine-grained BaTiO3 ceramics on the electrical properties were investigated. A change from the tetragonal to pseudocubic structure gradually takes place with the decrease of GS. As the GS increased from 96 to 194 nm, the dielectric constant increased from 1300 to 1560. The temperature capacitance coefficients satisfied the EIA X7R specifications for all the samples. Impedance analysis proved that the fine-grained ceramics have higher activation energy for both grain and grain boundary. The remnant polarization (P r ) values decrease with the decreasing of the GS, which is ascribed that the increasing of the grain boundary and internal stress would weaken the polarization of the direction of electric field. The grain boundary and defects have the pinning effects on the domain, leading the increase in E c .

0.55Bi 0.5 Na 0.5 TiO 3 -0.45Ba 0.85 Ca 0.15 Ti 0.85 Zr 0.1 Sn 0.05 O 3 - x wt%MgO ceramics were prepared by solid state route and their phase compositions and dielectric properties were investigated with the focus on improving energy storage density for capacitor applications. The XRD data results reveal that all samples possess a pure perovskite phase and some secondary phases of MgO and Mg 2 TiO 4 can be observed in the MgO doped samples. The frequency dispersion gradually disappears by the addition of MgO and MgO doped samples show a diffuse phase transition behavior. Dielectric breakdown strength of the samples are greatly improved with the increasing content of MgO. The sample with x = 5 shows a high dielectric breakdown strength of 18.97 kV/mm, a high discharge energy density of 1.62 J/cm 3 and a high energy efficiency of 79.51%, making it most suitable for application as high energy storage density capacitors.

Magnetoelectric composite ceramics of Ba 0.9 Ca 0.1 Ti 0.9 Zr 0.1 O 3 (BCZT) with high dielectric constant and Co 0.8 Ni 0.1 Zn 0.1 Fe 2 O 4 (CNZF) with high saturation magnetizations were synthesized via the solid state reaction method. The phase compositions and surface morphology of the composites were investigated using X-ray diffractometer (XRD), Scanning Electronic Microscopy (SEM) and Energy Dispersive Spectrometer (EDS). The dielectric, magnetic, and magnetoelectric properties of the composites were also investigated, and the properties of the composites could be adjusted by the ferrite content. The higher dielectric constant of BCZT/CNZF laminated composites are mainly attributed to the Maxwell-Wagner polarization. Compared with the magnetoelectric particulate composites, the magnetoelectric laminated composites have higher resistivities and lower leakage currents. The largest magnetoelectric coefficient of the laminated composites reaches up to 21.73 mV/cm Oe at 1100 Oe, which is twenty times as large as that of the particulate composites (1.45 mV/cm Oe).

In this paper, Ba 0.4 Sr 0.6 TiO 3 was added in the (K 0.4425 Na 0.52 Li 0.0375 )(Nb 0.87 Ta 0.06 Sb 0.07 )O 3 ceramics to improve the temperature stability. The phase structure, microstructure, dielectric, diffuse phase transition, relaxor behavior and temperature stability of (1− x )(K 0.4425 Na 0.52 Li 0.0375 ) (Nb 0.87 Ta 0.06 Sb 0.07 )O 3 - x Ba 0.4 Sr 0.6 TiO 3 (abbreviated as (1− x )KNLNTS- x BST)ceramics were investigated. The phase structure of these ceramics changed from tetragonal phase to cubic phase with Ba 0.4 Sr 0.6 TiO 3 additives. A significant reduction in the temperature dependence of relative permittivity occurred at x = 0.15, with Δ C / C 298K was around ±15% over the temperature range 273–528 K, and loss tangent, tanδ ≤ 0.03. The result indicated that this material may have great potential for a variety of high temperature applications. The diffuse phase transition and the temperature of the maximum dielectric permittivity shifting toward higher temperature with increasing frequency, which were observed in the (1− x )KNLNTS- x BST solid solution. The dielectric relaxor behavior obeyed a modified Curie-Weiss law. The dielectric relaxor was attributed to the appearance of polar nanoregions owing to the formation of random fields. The ferroelectric characteristic decreased with the addition of BST. These results confirmed that the (1− x )KNLNTS- x BST ceramics can be regarded as an alternative for high temperature lead-free piezoelectrics.

0.475BNT-0.525BCTZ-xwt%MgO ceramics were densified by microwave sintering method and their phase compositions and dielectric properties were investigated. The XRD results reveal that all samples possess a perovskite structure and the secondary phase of MgO can be observed in the MgO-doped samples. The maximum polarization of the MgO-doped samples sintered by microwave sintering are higher than that of the samples sintered by traditional sintering, thus a higher energy storage density can be achieved. The dielectric breakdown strength of the samples are greatly improved with the increasing content of MgO. The x=5 sample exhibits a high dielectric breakdown strength of 17.91 kV/mm and a high energy storage density of 1.37 J/cm3.

Polycrystalline (Ba0.9Bi0.1)(Ti0.9Al0.1)O3 (BBTA) ceramic is synthesized by solid state reaction method. XRD studies confirm the formation of single phase composition. Detailed studies of dielectric and impedance properties of the material in the wide range of frequency (20–2 MHz) and temperature (225–400 °C) shows that dielectric properties are strongly temperature and frequency dependent. The circle centers of Cole–Cole plots between e′ and e″ is located on the e′ axis, confirming the monodispersive nature of the relaxation processes for hopping electrons. The plots of Z″ and M″ are disperated with increase in frequency at different temperature, which proves the dielectric relaxation. The value of non-exponential parameter β can be determined by the full width-at-half-maximum of M″/M″ max spectrum (β = 1.14), indicating that the relaxation process for the sample is Debye-type relaxation phenomena in agreement with the observation from complex permittivity spectrum. The ac conductivity can be explained by the non-overlapping small polaron tunneling model.

(1−x)BaTiO3-xBiFeO3 ((1−x)BT-xBF) (x = 0–0.08) ceramics are synthesized via the conventional solid state method. And the influences of BF on the crystal structure, micromorphology and dielectric properties of BT ceramics have been investigated. X-ray diffractometer (XRD) and Raman spectra demonstrate a systematically structural transition from tetragonal to pseudo-cubic phase occurs from 0 ≤ x ≤ 0.08. The grain size of the samples becomes smaller and more uniform with the elevation of x. Dielectric behaviors display that the samples with x = 0, 0.06, and 0.08 belong to normal ferroelectric, diffused ferroelectric, and relaxor ferroelectric, respectively. High frequency independent conductivity arises for x = 0.06 and x = 0.08 due to the mobility of O2− ions and the defects generated in grain and grain boundary, which is in association with hopping of charge carriers along the Fe2+- V o ¨ -Fe3+ chain and between Fe2+ and Fe3+ ions, respectively, indicate different hopping process for electrons. The polarization-electric loops become narrow, demonstrate that there are the paraelectric and cubic phase exist in the ceramics, which is in agreement with the XRD patterns and Raman spectra of the BT-BF ceramics.