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.

Ta-doped 0.90BaTiO3–0.10(Bi0.5Na0.5)TiO3 ceramics were successfully prepared by conventional solid-state reaction method and studied to satisfy super-broad temperature stability. The effects of Ta2O5 doping on the dielectric properties and microstructures were thoroughly investigated. Ta plays an important role in the formation of core–shell structure because of chemical inhomogeneity, which gives rise to the weak temperature dependence of dielectric properties. The samples with the additon of 1.5 mol% Ta2O5 satisfy the X9R specification, exhibiting an optimum dielectric behavior of εr ~ 2100, tanδ ~ 1.6% at room temperature, which is a promising candidate material for X9R MLCC applications.

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.

Correction for ‘BaTiO3–BiYbO3 perovskite materials for energy storage applications’ by Zhengbo Shen et al., J. Mater. Chem. A, 2015, 3, 18146–18153.

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.

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.

Organic–inorganic 0–3 nanocomposites, which combine the potentially high dielectric strength of the organic matrix and the high dielectric permittivity of the inorganic filler, are extensively studied as energy-storage dielectrics in high-performance capacitors. In this study, a gradated multilayer BaTiO3/poly(vinylidene fluoride) thin film structure is presented as a means to achieve both a higher breakdown strength and a superior energy-storage capability. The central layer of this film, designed to provide high electric displacement, is composed of a high volume fraction of 6–10 nm BTO nanocrystals produced by a TEG-sol method. The small particle size contributes to a high dispersibility of the nanocrystals in polymer media, as well as a high interfacial area to mitigate the local electric field concentration. The outer layers of the structure are predominantly PVDF, with a significantly low volume fraction of BTO, taking advantage of the high dielectric strength of pure PVDF at the electrode–nanocomposite interface. The film is mechanically flexible, and can be removed from the substrate, with total thicknesses in the range of 1.2–1.5 μm. Parallel plate capacitance devices exhibit highly improved dielectric performances with low-frequency permittivity values of 20–25, a maximal discharge energy density of 19.37 J cm−3 and dielectric (breakdown) strengths of up to 495 kV mm−1.

Novel perovskite-type (1 − x)BaTiO3–xBiYbO3 solid solutions with x = 0.00–0.20 were synthesized using conventional solid-state reaction methods. A systematic structural change from ferroelectric tetragonal to pseudo-cubic phase was observed at about x = 0.050–0.051 at room temperature. Dielectric measurements revealed a gradual change from normal ferroelectric behavior to highly diffusive and dispersive relaxor-like characteristics, wherein the phase transition temperature shifted to a higher temperature with increasing frequency. With an increase in the BiYbO3 content, the nonlinearity of the (1 − x)BaTiO3–xBiYbO3 ceramic was weakened obviously. The bulk ceramics were characterized by high polarization maxima and low remnant polarization, which exhibit slim P–E hysteresis loops. The results demonstrate that the (1 − x)BaTiO3–xBiYbO3 ceramics are promising lead-free relaxor materials for energy storage applications.

Correction for ‘Flexible BaTiO3/PVDF gradated multilayer nanocomposite film with enhanced dielectric strength and high energy density’ by Y. N. Hao et al., J. Mater. Chem. C, 2015, 3, 9740–9747.

Perovskite-type alkaline niobate nanofibers were prepared by electrospinning. KNbO3 nanofibers with lower BET exhibit higher photocatalytic efficiency than NaNbO3 with similar phase structure and morphology. The internal electric field, which does not exist in antiferroelectric NaNbO3, induced by spontaneous polarization in ferroelectric KNbO3 can promote the separation and accelerate the movement of photogenerated charge carriers.

SrTiO3 nanocubes and their hyperstable nanocrystalline sols were synthesized by a rapid sol-precipitation method under atmospheric pressure. Using triethylene glycol (TEG) to control the hydrolysis rate of tetrabutyl titanate, the SrTiO3 nanocrystalline sol was obtained in as little time as 2 h. The formation kinetics of the SrTiO3 nanocubes indicated that controlled hydrolysis is critical to the generation of a well defined cubic shape. The Fourier transform infrared (FT-IR) spectrum confirms the existence of TEG molecules on the surface of the particles and explains the high dispersion of the nanocubes in polar solvents. Owing to the large specific surface area (99.065 m2 g−1), cubic SrTiO3 nanocrystals showed enhanced photocatalytic activity. A high-quality SrTiO3 nanocrystal film was prepared by spin-coating of the hyperstable sol at 100–160 °C, providing a new low-temperature route for the fabrication of perovskite thin films.

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.

0.65CaTiO3–0.35Sm0.9Nd0.1AlO3 (CTSA) ceramic nanopowders were synthesized via sol–gel method using the ethylene diamine tetraacetic acid as a chelating agent. Thermal analysis, Fourier transform infrared spectroscopy and X-ray diffraction were used to character the decomposition of precursor and phase transformation process of derived oxide powders. Single phase and well-crystallized 0.65CaTiO3–0.35Sm0.9Nd0.1AlO3 powders with particle size of 30–40 nm were obtained by calcination at 800 °C. Dense ceramic was successfully obtained from the ultrafine powders sintered at 1,325 °C, almost 100 °C lower than 1,415 °C required for conventional powders. Compared with those prepared by conventional solid-state method, the CTSA ceramics derived from sol to gel process sintered at a lower temperature showed better microwave dielectric properties of εr ~ 39, Q × f over 50,000 GHz and small τf ~ −7.1 ppm/K.

(Na0.52 K0.44Li0.04)(Nb0.86Ta0.06Sb0.08)O3 (LTS-KNN) nano-powders with the size of 11–34 nm were prepared by a sol–gel method. Using the nano-powders, LTS-KNN ceramics with fine grain size of 200–400 nm and high density were fabricated by spark plasma sintering. The satisfied piezoelectricity is obtained, such as d*33 ~ 481 pm/V, d33 ~ 296 pC/N, Kp ~ 49.7 %, ε33T/ε0 ~ 920, tanδ ~ 0.025 at 1 kHz and relative density is 99.4 %, respectively. It is shown that nano-powders are suitable to prepare fine-grained potassium-sodium niobate ceramics with satisfied properties.

High aspect-ratio Li2ZrO3 nanotube (NT) layers were obtained by hydrothermal synthesis in LiOH solution using anodic ZrO2 NT arrays as templates. Characterizations of SEM, XRD, and TEM were performed. The results showed that tetragonal Li2ZrO3 NTs arrays containing a little monoclinic ZrO2 can be obtained using this simple method. The mean diameter of the NTs is approximately 150 nm. The alkalinity of hydrothermal solution was proved to have significant effect on the formation of the Li2ZrO3 NT arrays. Under different alkalinity, different growth mechanisms dominated the formation of the nanotubular layers.

Two-step anodization is a novel method to fabricate graded nanotube arrays with particular morphologies. Through tailoring the electrochemical conditions, graded TiO2 nanotube arrays can be formed by two-step anodization. The growth mechanism of graded TiO2 nanotube arrays and influential factors in two-step anodization are investigated. We find that the nature of electrolyte used in the different anodization steps strongly influences the formation of graded nanotubular structure. In order to form graded TiO2 nanotube arrays, proper anodization sequence must be used: Step-1 anodization in the electrolyte which can produce higher electric filed intensity and faster chemical dissolution rate. Followed by Step-2 anodization in the electrolyte which can produce lower electric filed intensity and slower chemical dissolution rate.

In this study, well-ordered nanotubes of titania were fabricated by anodic oxidation of pure titanium foils in HF aqueous solution. Fe-SEM images indicate the average nanotubes diameter is ∼100 nm with a thickness of about 200 nm. Nanotube arrays of barium titanate and barium strontium titanate were synthesized under hydrothermal condition at 200 °C taking above-oxidized titania nanotubes as templates. In contrast to porous alumina membranes obtained by others using similar approaches, a different morphology was obtained in the current study. The nanotube arrays of barium titanate and barium strontium titanate may have many potential applications in microelectronics.

The formation of titanium oxide nanotube arrays on titanium substrates was investigated in HF electrolytes. Under optimized electrolyte and oxidation conditions, well-ordered nanotubes of titania were fabricated. Topologies of the anodized titanium change remarkably along with the changing of applied voltages, electrolyte concentration and oxidation time. Electrochemical determination and scanning electron microscope indicate the nanotubes are formed due to the competition of titania formation and dissolution under the assistance of electric field. A possible growth mechanism has also been presented.

The additions of SnO2 and ZrO2 are beneficial to improve the piezoelectric and dielectric properties of the reducing atmosphere fired (K0.5Na0.5)NbO3-based ceramics. The degradation of electrical properties when the pure (Na0.52K0.45Li0.03)NbO3 ceramics sintered in reducing atmosphere is mainly caused by the increasing of oxygen vacancy concentration, as low oxygen partial pressure promote the formation of oxygen vacancy. The 0.3 mol% SnO2 and 0.3 mol% ZrO2 co-modified ceramics sintered in reducing atmosphere exhibit excellent electrical properties (d33 = 198 pC/N, kp = 31.5%, ε33T/ε0 = 304, and tanδ = 0.022), which are comparable to the air fired ceramics with the same composition (d33 = 206 pC/N, kp = 32.6%, ε33T/ε0 = 590, and tanδ = 0.020). By thermally stimulated depolarization current technique, it can be demonstrated that the reduced fired doped ceramics have similar concentration of oxygen vacancy and defect dipole with the air fired ceramics due to the substitution of Sn and Zr into the A-sites and B-sites of perovskite structure. This study not only demonstrate the Sn and Zr co-doped KNN-based systems could possibly co-fire with base metal inner electrode but also broaden the selection of low-cost and eco-friendly materials for multilayer piezoelectric devices.

Correction for ‘Flexible BaTiO3/PVDF gradated multilayer nanocomposite film with enhanced dielectric strength and high energy density’ by Y. N. Hao et al., J. Mater. Chem. C, 2015, 3, 9740–9747.

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.

Novel perovskite-type (1 − x)BaTiO3–xBiYbO3 solid solutions with x = 0.00–0.20 were synthesized using conventional solid-state reaction methods. A systematic structural change from ferroelectric tetragonal to pseudo-cubic phase was observed at about x = 0.050–0.051 at room temperature. Dielectric measurements revealed a gradual change from normal ferroelectric behavior to highly diffusive and dispersive relaxor-like characteristics, wherein the phase transition temperature shifted to a higher temperature with increasing frequency. With an increase in the BiYbO3 content, the nonlinearity of the (1 − x)BaTiO3–xBiYbO3 ceramic was weakened obviously. The bulk ceramics were characterized by high polarization maxima and low remnant polarization, which exhibit slim P–E hysteresis loops. The results demonstrate that the (1 − x)BaTiO3–xBiYbO3 ceramics are promising lead-free relaxor materials for energy storage applications.

Organic–inorganic 0–3 nanocomposites, which combine the potentially high dielectric strength of the organic matrix and the high dielectric permittivity of the inorganic filler, are extensively studied as energy-storage dielectrics in high-performance capacitors. In this study, a gradated multilayer BaTiO3/poly(vinylidene fluoride) thin film structure is presented as a means to achieve both a higher breakdown strength and a superior energy-storage capability. The central layer of this film, designed to provide high electric displacement, is composed of a high volume fraction of 6–10 nm BTO nanocrystals produced by a TEG-sol method. The small particle size contributes to a high dispersibility of the nanocrystals in polymer media, as well as a high interfacial area to mitigate the local electric field concentration. The outer layers of the structure are predominantly PVDF, with a significantly low volume fraction of BTO, taking advantage of the high dielectric strength of pure PVDF at the electrode–nanocomposite interface. The film is mechanically flexible, and can be removed from the substrate, with total thicknesses in the range of 1.2–1.5 μm. Parallel plate capacitance devices exhibit highly improved dielectric performances with low-frequency permittivity values of 20–25, a maximal discharge energy density of 19.37 J cm−3 and dielectric (breakdown) strengths of up to 495 kV mm−1.

Correction for ‘BaTiO3–BiYbO3 perovskite materials for energy storage applications’ by Zhengbo Shen et al., J. Mater. Chem. A, 2015, 3, 18146–18153.

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.