A novel lead-free (1 – x)CaTiO3-xBiScO3 linear dielectric ceramic with enhanced energy-storage density was fabricated. With the composition of BiScO3 increasing, the dielectric constant of (1 – x)CaTiO3-xBiScO3 ceramics first increased and then decreased after the composition x > 0.1, while the dielectric loss decreased first and increased. For the composition x = 0.1, the polarization was increased into 12.36 μC/cm2, 4.6 times higher than that of the pure CaTiO3. The energy density of 0.9CaTiO3-0.1BiScO3 ceramic was 1.55 J/cm3 with the energy-storage efficiency of 90.4% at the breakdown strength of 270 kV/cm, and the power density was 1.79 MW/cm3. Comparison with other lead-free dielectric ceramics confirmed the superior potential of CaTiO3–BiScO3 ceramics for the design of ceramics capacitors for energy-storage applications. First-principles calculations revealed that Sc subsitution of Ti-site induced the atomic displacement of Ti ions in the whole crystal lattice, and lattice expansion was caused by variation of the bond angles and lenghths. Strong hybridization between O 2p and Ti 3d was observed in both valence band and conduction band; the hybridization between O 2p and Sc 3d at high conduction band was found to enlarge the band gap, and the static dielectric tensors were increased, which was the essential for the enhancement of polarization and dielectric properties.Keywords: dielectric; energy storage; ferroelectric; first-principles calculations; lead-free ceramics;

•Ultra fine-grained Ba0.4Sr0.6TiO3 ceramics were fabricated.•Low sintering temperature and high breakdown strength.•Polarization decreases, efficiency increases.•Utilization in multilayer devices for larger energy density possible.Fine-grained Ba0.4Sr0.6TiO3 ceramics with and without dopants were fabricated by two-step sintering method. Densities of fine-grained ceramics were found lower than those of coarse-grained ceramics, while the breakdown strength improved. With ZnO-Li2O sintering aids doped, the sintering temperature of ceramics decreased to 1200 °C. Their grain size is 219 nm, energy density is 0.564 J/cm3 and AC breakdown strength is 198.8 kV/cm, which is close to Ba0.4Sr0.6TiO3 ceramics obtained by SPS, and much higher than normal BST ceramics. The polarization of ceramics under the same electric field decreases with miniaturization of grain size, but the energy storage efficiency increases. Although smaller polarization due to small grain size is a disadvantage to energy density of bulk material, the features of low sintering temperature, traditional sintering route and small grain size jointly make the utilization in multilayer devices possible, thereby larger energy density can be achieved.

P(VDF-HFP)/PMMA composite films were fabricated using a blending and hot-molding method and investigated using both experimental and theoretical methods. The extended Flory–Huggins model were adopted to study the Gibbs energy, miscibility, and phase composition of binary mixture, and results showed favorable interactions and compatibility between P(VDF-HFP) and PMMA. The dielectric constant and loss of blend films were reduced compared to pristine films. The ferroelectric hysteresis loops of blend films are much slimmer than that of pristine P(VDF-HFP) films. The discharged energy density of 11.2 J/cm3 with the efficiency of 85.8% was obtained in the P(VDF-HFP)/PMMA blend films with 42.6 vol% PMMA at the electric field of 475 MV/m. The discharged energy density of blend film is 2.6 times of that of pristine film, while the energy storage efficiency is 2.07 times higher than that of pristine film. The origin of enhancement in the dielectric energy storage properties were analyzed using Fourier transform infrared spectra and atomistic simulation. FT-IR results showed γ–phase of P(VDF-HFP) was induced in blend films with a relative amount of 93.6%, comparing with the pristine P(VDF-HFP) films. The van der Waals forces and hydrogen bonding at the interface and the chain entanglement were responsible for the miscibility and stabilization of γ–phase, strengthening the energy storage properties.

Polymer-ceramic nanocomposites play an essential role in pulsed power system, due to their ultrahigh power density and fast charging–discharging capability. They also hold strong potential for improving the performance in energy storage capacitors, hybrid electric vehicles and kinetic energy weapons, since they contain a high-breakdown-strength polymer matrix and high-dielectric-permittivity ceramic nanofillers and thus can reach a high level of energy-storage density. In this work, through a finite element method and a phase field model, we theoretically analyze the nanocomposites with enhanced dielectric permittivity and dielectric breakdown strength by microstructure design of ceramic nanofillers, which covers the orientation, morphology and arrangement of nanofillers. Results indicate that the orientation of ceramic nanofibers has significant influence on the dielectric permittivity and breakdown strength of nanocomposites. The comparison of nanoparticles and nanofibers reveals the increase extent of interactions between polymer matrix and ceramic nanofillers can enhance the dielectric breakdown strength of the nanocomposites. Based on the results above, two sandwich structures consisting of both nanoparticles and nanofibers have been constructed to pursue a higher energy storage density.

Polymer-ceramic nanocomposites play an essential role in the application of pulsed power system, due to their ultrahigh power density and fast charging–discharging capability. It is very promising for them to be applied in energy storage capacitors and hybrid electric vehicles for the recent progressing in the improving energy density. The volume fraction, morphology, size, aspect ratio and distribution of ceramic particles have been reported to have significant effect on the dielectric response and breakdown strength of nanocomposites, which are two main factors that determine the energy density of nanocomposites. In this study, we introduce a quantified method to describe the distribution of ceramic nanoparticles in polymer matrix, then focus on the effect of nanoparticles distribution on dielectric response and breakdown strength of nanocomposites through finite element method and phase field method. Results indicate that the non-uniform distribution of ceramic nanoparticles will aggravate the concentration of local electric field, thus slightly enhance the dielectric response but seriously decrease the breakdown strength of nanocomposites. To verify the size effect of ceramic particles on breakdown strength of nanocomposites, three types of well distributed nanoparticles with different diameter of particles have also been calculated using the same method.

GN/BT nanocomposites were fabricated via colloidal processing methods, and ceramics were sintered through two-step sintering methods. The microstructure and morphology were characterized by X-ray diffraction, high-resolution transmission electron microscopy, and field emission scanning electron microscopy. XRD analysis shows that all samples are perovskite phases, and the lattice parameters a and c almost decrease linearly with the increase of graphene nanosheets. The dielectric properties were tested by using precision impedance. The maximum dielectric constant at the Curie temperature for the nanocomposites with graphene addition of 3 wt % is about 16 000, almost 2 times more than that of pure BaTiO3 ceramics. The relaxation, band structure, density of states, and charge density distribution of GN/BT superlattices were calculated using first-principles calculations for the first time, and results showed the strong hybrid interactions between C 2p states and O 2p and Ti 3d orbitals.Keywords: BaTiO3; dielectric; ferroelectric; first-principles; graphene

Lead-free (1 − x)BaTiO3–xBi(Zn2/3Nb1/3)O3 (x = 0.05–0.20) materials were fabricated via solid-state reactions. A pure perovskite pseudocubic structure is obtained for all compositions. Dielectric measurements reveal an intensified diffusion and relaxor-like characteristics from 5 mol% to 20 mol% Bi(Zn2/3Nb1/3)O3. Weakly coupled relaxor behavior is concluded from the exceptionally high activation energies of ∼0.20–0.22 eV from the Vogel–Fulcher model for x ≥ 0.10, which possibly results in the extremely low dielectric nonlinearity and extra slim polarization–electric field loops. An optimal discharged energy density of 0.79 J cm−3 with a high energy efficiency of 93.5% is achieved at 131 kV cm−1 for x = 0.15, which proves that the BaTiO3–Bi(Zn2/3Nb1/3)O3 material is a promising candidate for high energy storage applications.

•Core-shell BaTiO3@BiScO3 particles are fabricated via sol-precipitation.•Local compositionally graded structure is formed via controlled sintering.•Grain sizes and DC conductivities are suppressed.•Wide and flat dielectric-temperature plateau is achieved.•Discharged energy density and energy efficiency are enhanced.Core-shell BaTiO3@BiScO3 (BT@BS) particles were fabricated via a facile sol-precipitation method, with which bulk ceramics were prepared via conventional sintering. Pure perovskite phases of the BT@BS ceramics were confirmed by XRD patterns. Grain sizes and DC conductivities of the BT@BS ceramics are suppressed in comparison with pure BT. Dielectric-temperature measurements show that with the addition of BS, the tetragonal-orthorhombic and orthorhombic-rhombohedral peaks sequentially disappear with gradual broadening and dispersion of Curie peaks. Wide and flat dielectric-temperature plateau is achieved in the ceramic with 3 mol% BS coatings, which is due to the formation of local compositionally graded structure from the modulated diffusion of Bi and Sc. Weakened polarization nonlinearity and reduced hysteresis are achieved in the BT@BS ceramics, which contribute to enhanced energy storage capability. This work provides a generic avenue for fabricating temperature-stabilized dielectrics with improved energy storage density.

The electronic structure, lattice vibrations, and optical, dielectric and thermodynamic properties of BaTiO3/CaTiO3/SrTiO3 (BT/CT/ST) ferroelectric superlattices are calculated by using first-principles calculations. After relaxation, the lattice parameters are in good agreement with the experimental and other theoretical values within an error of 1%. The band structure shows an indirect band gap with a value of about 2.039 eV, and a direct band gap of 2.39 eV at the Γ point. The density of states and the electron charge density along the [001] axis are calculated and show the displacement of Ti ions along the [001] axis. The strong hybridization between O 2p and Ti 3d contributes to the ferroelectricity of BT/CT/ST ferroelectric superlattices. The Γ modes are stable, while the vibration modes at A, M, R, and X points are unstable governing the nature of phase transition. The static dielectric tensor including the ionic contribution is calculated and the permittivity parallel to the optical axis is found to be almost eight times more than the permittivity vertical to the axis, exhibiting strong anisotropy. The thermodynamic enthalpy, the free energy, the entropy, and the heat capacity are also investigated based on the phonon properties.

Dielectric capacitors with high energy density and low energy loss are of great importance in high power electric and electronic systems. Traditional BaTiO3 (BT) or its solid solutions have been widely explored as high energy density materials owing to their notably high dielectric constants. However, these materials often suffer from significant drawbacks of strong dielectric nonlinearity, low breakdown strength and high hysteresis loss, limiting the energy storage density and energy utilization efficiency. In this study, by using core-satellite structured nanocubic SrTiO3 (ST) decorated BT assemblies, a composite capacitor with enhanced breakdown strength and weaker dielectric nonlinearity was successfully fabricated in contrast with the pure ferroelectric BT ceramic, resulting in elevated energy storage density and high energy efficiency as extracted from the polarization-electric field loops. The mechanism behind the improved electric and dielectric performances was discovered to be the remarkable suppression of grain size owing to the existence of the ST nanocubes and also the ferroelectric relaxor behaviors arising from the local compositionally graded structure due to the controlled sintering and modulated diffusion of Sr. This work provided a new approach for fabrication of dielectric materials with promising high energy density and low loss.

Fine-grained BaTiO3-based ceramics with core–shell structures were prepared using the chemical coating method and the solid-state method. The sintering behavior and microstructure evolution were investigated for the samples prepared using different methods. The dielectric properties of modified BaTiO3 ceramics were also investigated, and the TEM–EDS results provided a detailed explanation for the different temperature coefficient of capacitance behaviors. In addition, the insulation resistivity for the ceramic samples under elevated temperature and high voltages was observed. The highly accelerated lifetime test results indicate that the samples prepared by the chemical coating method exhibited higher insulation resistance and a smaller degradation rate. Impedance analysis demonstrated that the grain boundary activation energy was much higher for the samples prepared by the chemical coating method.

BaTiO3-based dielectric ceramics with grain sizes of 100–120 nm were prepared by the chemical coating approach and are promising for the application of ultrathin multilayer ceramic capacitors. The doping effects of Mg on the microstructures and dielectric properties of the BaTiO3-based ceramics were investigated. The addition of Mg was beneficial for inhibiting the grain growth and improving sintering characteristics and improving the dielectric properties and reliability of the nano-BaTiO3-based ceramics. The highly accelerated lifetime test and thermally stimulated depolarization current were employed to study the resistance degradation and conduction mechanism of the Mg-doped BaTiO3 ceramics. It was determined that the reliability characteristics greatly depended on the Mg content. The addition of 2 mol% Mg was suitable for improving the reliability of the nano-BaTiO3-based ceramics, which is an important parameter for the application of multilayer ceramic capacitors. However, further increasing the addition amount of Mg decreased the performance of the BaTiO3-based ceramics.

Calcium barium zirconate titanate (Ba0.95Ca0.05Zr0.15Ti0.85O3, BCZT) ceramic particles were prepared by a conventional solid-state method. BCZT powders were modified by dopamine through a chemical coating method. The composite flexible films based on dopamine@BCZT and polyvinylidene fluoride were fabricated via a solution casting method. The microstructure and morphology were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, high-resolution transmission electron microscopy, and field emission scanning electron microscopy. A precision impedance analyzer and a dielectric withstand voltage test were used to test the dielectric constant, loss tangent, and breakdown strength. TEM results showed that dopamine was uniformly coated on the surface of BCZT particles with an average thickness of 20 nm. SEM results showed that the ceramic particles were dispersed homogeneously in the matrix. The dielectric constant increased with the increase of BCZT contents, while the loss tangent remained constant in the frequency range of 103 to 105 Hz. Different theoretical models were employed to predict the effective dielectric constants of the composite films, and the estimated results were compared with the experimental data. Weibull distribution was used to analyze the dielectric breakdown strength, and the results showed that the breakdown strength decreased then stayed over 60 kV mm−1.

Fine-grained BaTiO3-based ceramics of different grain sizes (118–462 nm) with core–shell structures were prepared by a chemical coating method, having good dielectric properties and gentle temperature stability. The grain size effect on the dielectric properties and insulation resistivity of modified fine-grained BaTiO3 ceramics under high temperatures and electric fields were investigated. The DC bias shows a strong effect on the dielectric properties with decreasing grain size. In the finest ceramics, the absolute value of the capacitance stability factor was the smallest, indicating that the modified-BaTiO3 ceramic capacitor with smaller grains had higher reliability under the DC bias voltage. The highly accelerated lifetime test results showed that with decreasing the grain size, samples exhibited higher insulation resistance under elevated temperatures and high voltages. Impedance analysis proved that the finer-grained ceramic with core–shell structure had higher activation energy for both grain and grain boundary, whereas the proportion of ionic conductivity was lower.

The interfacial structure and diffusion behavior between the dielectric layers (BaTiO3) and internal electrode layers (Ni) in X5R-type multilayer ceramic capacitors (MLCCs, from −55°C to 85°C, at a temperature capacitance coefficient within ±15%) with ultra-thin active layers (T = 1–3 µm) have been investigated by several microstructural techniques (SEM/TEM/HRTEM) with energy-dispersive x-ray spectroscopy (EDS). In the MLCC samples with different active layer thicknesses (1–3 µm), weak interfacial diffusion was observed between BaTiO3 and Ni. It was also found that the diffusion capability of Ni into the BaTiO3 layer was stronger than that of BaTiO3 to the Ni electrode, which indicated that the diffusion of Ni was the dominant factor for the interfacial diffusion behavior in the ultra-thin layered MLCCs. The mechanism of Ni diffusion is discussed in this study as well.

(Na0.85K0.15)0.5Bi0.5TiO3 (NKBT) thin films derived from different amounts of Na/K excess content were fabricated via an aqueous sol–gel method on a Pt(111)/Ti/SiO2/Si substrate, and the effect of Na/K excess content on the microstructure and electrical properties of the NKBT thin films was investigated. A second phase appears when Na/K excess content is below 20 mol%. Appropriated Na/K excess can enhance the polarization and dielectric properties due to compensation of Na/K loss that occurred during heat treatment. The 20 mol% excess derived NKBT thin film exhibits the best ferroelectric and dielectric properties with a remnant polarization (Pr) of 13.6 μC/cm2, and a coercive field (Ec) of 104.8 KV/cm, together with a dielectric constant of 406 and a dissipation factor of 0.064. Similar to the dielectric response change with Na/K excess content, the decreasing concentration of charged defects is the main reason resulting in the increase of the piezoelectric property. The film with a 20 mol% excess content exhibited an effective d33⁎ of about 56 pm/V. Also, the NKBT with a 20 mol% excess content exhibits the lowest current density of 5.6 × 10− 5 A/cm2 at 10 V.

Fine-grained BaTiO3-based ceramics of different grain sizes (118–462 nm) with core–shell structures were prepared by a chemical coating method, having good dielectric properties and gentle temperature stability. The grain size effect on the dielectric properties and insulation resistivity of modified fine-grained BaTiO3 ceramics under high temperatures and electric fields were investigated. The DC bias shows a strong effect on the dielectric properties with decreasing grain size. In the finest ceramics, the absolute value of the capacitance stability factor was the smallest, indicating that the modified-BaTiO3 ceramic capacitor with smaller grains had higher reliability under the DC bias voltage. The highly accelerated lifetime test results showed that with decreasing the grain size, samples exhibited higher insulation resistance under elevated temperatures and high voltages. Impedance analysis proved that the finer-grained ceramic with core–shell structure had higher activation energy for both grain and grain boundary, whereas the proportion of ionic conductivity was lower.

Calcium barium zirconate titanate (Ba0.95Ca0.05Zr0.15Ti0.85O3, BCZT) ceramic particles were prepared by a conventional solid-state method. BCZT powders were modified by dopamine through a chemical coating method. The composite flexible films based on dopamine@BCZT and polyvinylidene fluoride were fabricated via a solution casting method. The microstructure and morphology were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, high-resolution transmission electron microscopy, and field emission scanning electron microscopy. A precision impedance analyzer and a dielectric withstand voltage test were used to test the dielectric constant, loss tangent, and breakdown strength. TEM results showed that dopamine was uniformly coated on the surface of BCZT particles with an average thickness of 20 nm. SEM results showed that the ceramic particles were dispersed homogeneously in the matrix. The dielectric constant increased with the increase of BCZT contents, while the loss tangent remained constant in the frequency range of 103 to 105 Hz. Different theoretical models were employed to predict the effective dielectric constants of the composite films, and the estimated results were compared with the experimental data. Weibull distribution was used to analyze the dielectric breakdown strength, and the results showed that the breakdown strength decreased then stayed over 60 kV mm−1.

Dielectric capacitors with high energy density and low energy loss are of great importance in high power electric and electronic systems. Traditional BaTiO3 (BT) or its solid solutions have been widely explored as high energy density materials owing to their notably high dielectric constants. However, these materials often suffer from significant drawbacks of strong dielectric nonlinearity, low breakdown strength and high hysteresis loss, limiting the energy storage density and energy utilization efficiency. In this study, by using core-satellite structured nanocubic SrTiO3 (ST) decorated BT assemblies, a composite capacitor with enhanced breakdown strength and weaker dielectric nonlinearity was successfully fabricated in contrast with the pure ferroelectric BT ceramic, resulting in elevated energy storage density and high energy efficiency as extracted from the polarization-electric field loops. The mechanism behind the improved electric and dielectric performances was discovered to be the remarkable suppression of grain size owing to the existence of the ST nanocubes and also the ferroelectric relaxor behaviors arising from the local compositionally graded structure due to the controlled sintering and modulated diffusion of Sr. This work provided a new approach for fabrication of dielectric materials with promising high energy density and low loss.

The electronic structure, lattice vibrations, and optical, dielectric and thermodynamic properties of BaTiO3/CaTiO3/SrTiO3 (BT/CT/ST) ferroelectric superlattices are calculated by using first-principles calculations. After relaxation, the lattice parameters are in good agreement with the experimental and other theoretical values within an error of 1%. The band structure shows an indirect band gap with a value of about 2.039 eV, and a direct band gap of 2.39 eV at the Γ point. The density of states and the electron charge density along the [001] axis are calculated and show the displacement of Ti ions along the [001] axis. The strong hybridization between O 2p and Ti 3d contributes to the ferroelectricity of BT/CT/ST ferroelectric superlattices. The Γ modes are stable, while the vibration modes at A, M, R, and X points are unstable governing the nature of phase transition. The static dielectric tensor including the ionic contribution is calculated and the permittivity parallel to the optical axis is found to be almost eight times more than the permittivity vertical to the axis, exhibiting strong anisotropy. The thermodynamic enthalpy, the free energy, the entropy, and the heat capacity are also investigated based on the phonon properties.