Significant enhancement in breakdown strength and energy density of the BaTiO3/BaTiO3@SiO2 layered ceramics with strong interface blocking effect

The BaTiO₃/BaTiO₃@SiO₂ (BT/BTS) ceramics with layered structure, where grain size was about 1–2 μm in the BT layer while it was about 300–400 nm in the BTS layer, were fabricated by the tape-casting and lamination method. With the increasing of SiO₂ content in the BTS layer, the dielectric constant decreased gradually, and the breakdown strength was remarkably improved. Compared to the SiO₂-added BaTiO₃ bulk ceramics, the layered ceramics displayed significant enhancements in dielectric properties, breakdown properties and energy storage properties. The enhancement in dielectric properties was mostly attributed to the diluting effects created by this structure to SiO₂. Based on the finite element analysis with the dielectric breakdown mode, it was regarded that the electric field redistribution and the interface blocking effect led to the enhancement of breakdown strength. Finally, the maximum energy density of 1.8 J/cm³ was obtained at a breakdown strength of 301.4 kV/cm for the BT/BTS3 ceramic.     

Energy storage density and tunable dielectric properties of BaTi0.85Sn0.15O3/MgO composite ceramics prepared by SPS

(100-x) wt.% BaTi_0.85Sn_0.15O₃–x wt.% MgO (BTS/MgO) composite ceramics were prepared by spark plasma sintering (SPS) technology. Phase constitution, microstructure, dielectric and electrical energy storage properties of BTS/MgO composite ceramics were investigated. The samples prepared by SPS had smaller grain size and presented layer-plate substructure. Dielectric permittivity and dielectric loss of BTS/MgO composite ceramics decreased significantly with the content of MgO increasing, and dielectric tunability maintained a relatively high value (>45%). Meanwhile, the dielectric breakdown strength was improved when addition of MgO in BTS matrix, which resulted in a significant improvement of energy storage density. The high dielectric breakdown strength of 190 kV/cm, energy storage density of 0.5107 J/cm³ and energy storage efficiency of 92.11% were obtained in 90 wt.% BaTi_0.85Sn_0.15O₃–10 wt.% MgO composite ceramics. Therefore, BTS/MgO composites with good tunable dielectric properties and electrical energy storage properties could be exploited for energy storage and phase shifter device applications.     

Development of PLZT dielectrics on base metal foils for embedded capacitors

We have deposited Pb_0.92La_0.08Zr_0.52Ti_0.48O₃ (PLZT) films on nickel and copper substrates to create film-on-foil capacitors that exhibit excellent dielectric properties and superior breakdown strength. Measurements with PLZT films on LaNiO₃-buffered Ni foils yielded the following: relative permittivity of 1300 (at 25 °C) and 1800 (at 150 °C), leakage current density of 6.6 × 10^?9 A/cm² (at 25 °C) and 1.4 × 10^?8 A/cm² (at 150 °C), and mean breakdown field strength ≈2.5 MV/cm. With PLZT deposited directly on Cu foils, we observed dielectric constant ≈1100, dielectric loss (tan δ) ≈0.06, and leakage current density of 7.3 × 10^?9 A/cm² when measured at room temperature.     

Influence of sintering temperature on energy storage properties of BaTiO3–(Sr1−1.5xBix) TiO3 ceramics

The effect of sintering temperature on microstructure, dielectric properties and energy storage properties of BaTiO₃–(Sr_1?1.5xBi_x)TiO₃ (x = 0.09) (BT–SBT) ceramics was investigated. The sintering temperature has pronounced influence on the grain size, shrinkage, and dielectric properties of the BT–SBT ceramics. With increasing sintering temperature, the dielectric constant increases largely. However, the increasing tendency of the dielectric breakdown strength (BDS) is less noticeable but become more evident with the consideration of Weibull modulus. For the BT-SBT ceramics, the unreleased energy density decreases and the electric field stability of the energy storage efficiency enhances with the increase of sintering temperature.     

Testing media influences on the dielectric properties of lead sodium niobate glass-ceramics

The influences of testing media on the breakdown strength (BDS) and dielectric properties of glass-ceramics in the Na₂O–PbO–Nb₂O₅–SiO₂ system were investigated. This work was brought out by consideration of the electric conductance, dielectric constant and breakdown strength of different testing media, which are the main reasons for the different dielectric properties and BDS values of the identical dielectric sample. Leakage current (LC), P–E hysteresis loops, C–V curves and breakdown tests show that the BDS and the dielectric properties of the glass-ceramics could be optimized through using appropriate testing medium. It turns out that three favorable characteristics of the dielectric composites could be optimized in silicon/castor oil mixture: the lowest LC (LC = 6.72 × 10^?6 A, at E = 25 kV/mm), thin P–E hysteresis loops and low hysteresis. Furthermore, the highest BDS of the glass-ceramic was obtained in glycerin (BDS = 105.6 kV/mm with sample thickness of 0.108 mm) compared to other media.     

Microstructure and dielectric properties of SrTiO3 ceramics by controlled growth of silica shells on SrTiO3 nanoparticles

SrTiO₃@SiO₂ nanopowder was synthesized via a core-shell nano-scale technique that is known as the Stöber process. The effect of the SiO₂ concentration on microstructure, dielectric response and energy storage properties of SrTiO₃@SiO₂ ceramics was investigated. Transmission electron microscopy (TEM) results confirmed the formation of core–shell nanostructures with controlled shell thicknesses between 2 nm and 13 nm. After increasing SiO₂, a secondary phase with Sr₂TiSi₂O₈ appeared due to inter-diffusion reactions between the SrTiO₃ core and SiO₂ shells during the sintering process. The results show that both breakdown strength and energy density improved apparently. The homogeneous coating of silica on ST cores is considered to dominate the contribution to improved breakdown strength. The composition for SrTiO₃ coated with 2.5 wt% SiO₂ shows the maximum energy storage density (1.2 J/cm³) and a breakdown strength of 310 kV/cm. The former is higher than for pure SrTiO₃ (0.19 J/cm³). Measurements of the dielectric performance indicate that the SrTiO₃@SiO₂ ceramics possess good bias stabilities compared to pure ST ceramics.     

Effect of SiO2 additive on dielectric response and energy storage performance of Ba0.4Sr0.6TiO3 ceramics

SiO₂-added barium strontium titanate ceramics Ba_0.4Sr_0.6TiO₃-xwt%SiO₂ (x=0, 0.5, 1, 3, BSTSx) were prepared via a traditional solid state reaction method. The effect of SiO₂ additive on the microstructure, dielectric response and energy storage properties was investigated. The results confirmed that with the increase of SiO₂ additive, diffuse phase transition arises and the dielectric constant decreases. An equivalent circuit model and Arrhenius law were used to calculate the activation energy of grain and grain boundary, which indicated that the dielectric relaxation at high temperature was caused by oxygen vacancy. While appropriate SiO₂ additive led to improve the breakdown strength, further increase of SiO₂ deteriorated the energy storage because of the low densification. Finally, optimized energy storage performance was obtained for BSTS0.5 ceramics: dielectric constant of 1002, dielectric loss of 0.45%, energy density of 0.86 J/cm³ and energy storage efficiency of 79% at 134 kV/cm.     

Low dielectric loss of Bi-doped BaZr0.15Ti0.85O3 ceramics for high-voltage capacitor applications

BaZr_0.15Ti_0.85O₃ ceramics are prepared via the conventional solid state reaction method. The effects of Bi₂O₃·3TiO₂ doped on dielectric properties and breakdown strength of BaZr_0.15Ti_0.85O₃ ceramics are systematically discussed. Doping of Bi₂O₃·3TiO₂ can obviously improve the breakdown strength and reduce the dielectric loss of the material. It is attributed to the Bi³⁺ substituted Ba²⁺ is an unequal ion substitution, and two Bi³⁺ substitute three Ba²⁺ to produce an A vacancy, thereby increasing the lattice energy and promoting the diffusion and migration of the particles during the sintering process, promoting the sintering and reducing the sintering temperature. However, the dielectric constant of the material is decreased. When the amount of Bi₂O₃·3TiO₂ is 12 mol%, the minimum dielectric loss tanδ = 0.0009, the maximum breakdown strength is E_b = 15.09 kV/mm, the insulation resistivity is 3.52 × 10¹¹ Ω cm. The energy storage density of the BaZr_0.15Ti_0.85O₃ ceramic samples doped with Bi₂O₃·3TiO₂ varies from 0.008 J/cm³ to 0.012 J/cm³.     

Improvement in structural,dielectric and energy-storage properties of lead-free niobate glass-ceramic with Sm2O3

Phase evolution, microstructure, dielectric performance, polarization, breakdown strength as well as energy-storage behaviors for the lead-free niobates glass-ceramics with Sm₂O₃ were systematically investigated. Two crystallographic structures of tetragonal tungsten bronze and orthorhombic perovskite complex phases were obtained and Sm³⁺ entered into the crystalline phases. The optimal microstructure of the glass-ceramic was obtained with Sm₂O₃ of 2 mol%. Both dielectric constant and polarizability were enhanced with increasing Sm₂O₃. The breakdown strength and energy-storage behaviors of the glass-ceramics were also improved by increased Sm₂O₃. The highest breakdown field of 21.2 kV/mm, the highest charged (0.74 J/cm³) and discharged energy density (0.45 J/cm³) were obtained in the glass-ceramic with 2 mol% Sm₂O₃. It is due to the reduced interfacial polarization in this particular composition.     

Effects of phase constitution and microstructure on energy storage properties of barium strontium titanate ceramics

Barium strontium titanate (Ba_0.3Sr_0.7TiO₃, BST) ceramics have been prepared by conventional sintering (CS) and spark plasma sintering (SPS). The effects of phase constitution and microstructure on dielectric properties, electrical breakdown process and energy storage properties of the BST ceramics were investigated. The X-ray diffraction analysis and dielectric properties measurements showed that the cubic and tetragonal phase coexisted in the SPS sample while the CS sample contained only tetragonal phase. Much smaller grain size, lower porosity, fewer defects and dislocation were observed in SPS samples, which greatly improved the electrical breakdown strength of the Ba_0.3Sr_0.7TiO₃ ceramics. The enhanced breakdown strength of the SPS samples resulted in an improved maximum electrical energy storage density of 1.13 J/cm³ which was twice as large as that of the CS sample (0.57 J/cm³). Meanwhile, the energy storage efficiency was improved from 69.3% to 86.8% by using spark plasma sintering.     

Fast discharge and high energy density of nanocomposite capacitors using Ba0.6Sr0.4TiO3 nanofibers

Nanocomposites combining high breakdown strength (BDS) polymer and high dielectric permittivity ceramic fillers have shown great potential for pulsed power application. Here a new composite material based on surface-functionalized Ba_0.6Sr_0.4TiO₃ nanofibers/poly(vinylidene fluoride) (BST NF/PVDF) has been prepared by solution casting. The nanocomposites containing 2.5 vol% isopropyl dioleic(dioctylphosphate) titanate (NDZ 101)-functionalized BST NF (N-h-BST NF) have large energy density of 6.95 J cm⁻³ at 380 MV m⁻¹, which is 1.85 times larger than that of the pure PVDF at the same electric field. Also, the discharge speed of the nanocomposites containing 7.5 vol% N-h-BST NF is approximately 0.11 μs. The good properties, together with the large energy density and fast discharge speed, make this material a promising candidate for pulsed power capacitor.     

Enhanced dielectric and energy-storage properties in BiFeO3-modified Bi0.5(Na0.8K0.2)0.5TiO3 thin films

Lead free Bi_0.5(Na_0.8K_0.2)_0.5TiO₃ thin films doped with BiFeO₃ (abbreviated as BNKT-xBFO) (x = 0, 0.02, 0.04, 0.08, 0.10) were deposited on Pt(111)/Ti/SiO₂/Si substrates by sol-gel/spin coating technique and the effects of BiFeO₃ content on the crystal structure and electrical properties were investigated in detail. The results showed that all the BNKT-xBFO thin films exhibited a single perovskite phase structure and high-dense surface. Reduced leakage current density, enhanced dielectric and ferroelectric properties were achieved at the optimal composition of BNKT-0.10BFO thin films, with a leakage current density, dielectric constant, dielectric loss and maximum polarization of < 2 × 10⁻⁴ A/cm³, ~ 978^, ~ 0.028 and ~ 74.13 μC/cm² at room temperature, respectively. Moreover, the BNKT-0.10BFO thin films possessed superior energy storage properties due to their slim P-E loops and large maximum polarization, with an energy storage density of 22.12 J/cm³ and an energy conversion efficiency of 60.85% under a relatively low electric field of 1200 kV/cm. Furthermore, the first half period of the BNKT-0.10BFO thin film capacitor was about 0.15 μs, during which most charges and energy were released. The large recoverable energy density and the fast discharge process indicated the potential application of the BNKT-0.10BFO thin films in electrostatic capacitors and embedded devices.     

Lead-free BaTiO3-Bi0.5Na0.5TiO3-Na0.73Bi0.09NbO3 relaxor ferroelectric ceramics for high energy storage

A series of (1-x)(0.65BaTiO₃-0.35Bi_0.5Na_0.5TiO₃)-xNa_0.73Bi_0.09NbO₃ ((1-x)BBNT-xNBN) (x = 0–0.14) ceramics were designed and fabricated using the conventional solid-state sintering method. The microstructure, dielectric property, relaxor behavior and energy storage property were systematically investigated. X-ray diffraction results reveal a pure perovskite structure and dielectric measurements exhibit a relaxor behavior for the (1-x)BBNT-xNBN ceramics. The slim polarization electric field (P-E) loops were observed in the samples with x ≥ 0.02 and the addition of Na_0.73Bi_0.09NbO₃ (NBN) could decrease the remnant polarization (P_r) of the (1-x)BBNT-xNBN ceramics obviously. The sample with x = 0.08 exhibits the highest energy storage density of 1.70 J/cm³ and the energy storage efficiency of 82% at 172 kV/cm owing to its submicron grain size and high relative density. These results show that the (1-x)BBNT-xNBN ceramics may be promising lead-free materials for high energy storage density capacitors.     

Effect of layered structure on dielectric properties and energy storage density in xBa0.7Sr0.3TiO3-SrTiO3 multilayer ceramics

xBa_0.7Sr_0.3TiO₃-SrTiO₃ (BST-ST) multilayer ceramics with different BST layers (x=1, 3, 5) were designed and fabricated by lamination of Ba_0.7Sr_0.3TiO₃ (BST) and SrTiO₃ (ST) tapes. Dielectric and energy storage properties of the multilayer ceramics were investigated. BST-ST multilayer ceramics exhibited enhanced temperature- and frequency-stability of dielectric properties, accompanying high permittivity (~2000) and low dielectric loss (<0.005) at room temperature. P-E loops revealed that BST-ST multilayer ceramics displayed low remnant polarization and favorable maximum polarization. The optimal energy storage performance was obtained in the composition of x=5 with dielectric breakdown strength of 220 kV/cm and energy storage density of 2.3 J/cm³. These results indicate that BST-ST multilayer ceramics can be a favorable candidate for dielectric capacitor applications.     

Electrical properties of new tin dioxide varistor ceramics at high currents

New dense SnO₂-based varistor ceramics with high nonlinear current–voltage characteristics (nonlinearity coefficients are of approximately 50) in a system of SnO₂–CoO–Nb₂O₅–Cr₂O₃–Y₂O₃–SrO–MgO are reported. The current–voltage behaviour at high currents is studied by using exponential voltage pulses. The obtained SnO₂ varistor ceramics exhibit low grain resistivity values of 0.23–0.64 ohm cm. To date, such values are the lowest known for SnO₂ varistors, and are closely approaching the grain resistivity of the ZnO varistor. The current–voltage characteristics of the obtained SnO₂-based varistor materials are reproducible in a wide current range from 10^?11 to approximately 10⁴ A cm^?2. The minimum current density and the minimum electric field necessary to cause the irreversible electrical breakdown are measured. It is established that a decrease in the grain resistivity leads to an increase in the minimum current density necessary for irreversible electrical breakdown to occur.     

Effect of crystallization temperature on dielectric and energy-storage properties in SrO-Na2O-Nb2O5-SiO2 glass-ceramics

The SrO-Na₂O-Nb₂O₅-SiO₂ (SNNS) glass-ceramics were prepared through the melt-quenching combined with the controlled crystallization technique. XRD results showed Sr₆Nb₁₀O₃₀, SrNb₂O₆, NaSr₂Nb₅O₁₅ with tungsten bronze structure and NaNbO₃ with the perovskite structure. With the decrease of crystallization temperature, dielectric constant firstly increased and then decreased, while breakdown strength (BDS) was increased. High BDS of the glass-ceramics is attributed to the dense and uniform microstructure at low crystallization temperature. The optimal dielectric constant of 140±7 at 900 °C and BDS of 2182±129 kV/cm at 750 °C were obtained in SNNS glass-ceramics. The theoretical energy-storage density was significantly improved up to the highest value of 15.2±1.0 J/cm³ at 800 °C, which is about 5 times than that at 950 °C. The discharged efficiency increased from 65.8% at 950 °C to 93.6% at 750 °C under the electric field of 500 kV/cm by decreasing crystallization temperature.     

Effects of Sr substitution for Ba on dielectric and energy-storage properties of SrO-BaO-K2O-Nb2O5-SiO2 glass-ceramics

In this work, [xSrO, (1 − x)BaO]-K₂O -Nb₂O₅-SiO₂ (SBKNS, x = 0.2, 0.4, 0.6, 0.8) glass-ceramics were synthesized through the controlled crystallization method. The phase structure, dielectric and energy-storage properties were systematically studied through the Sr substitution for Ba. It was found that the dielectric properties were improved due to the formation of solid liquid phase Sr_0.5Ba_0.5Nb₂O₆. Breakdown strength firstly increases and then decreases, which strongly depends on the variation in interfacial polarization. The highest value of breakdown strength reaches 1828 ± 88 kV/cm for x = 0.4, which is attributed to more uniform and dense microstructure and lower interfacial polarization. Correspondingly, the optimized theoretical energy-storage density reaches up to 17.45 ± 0.74 J/cm³. The maximum of discharged energy-storage density of 1.45 J/cm³ from P-E loop was acquired under electric field of 500 kV/cm. Moreover, discharged power density of the capacitor was evaluated and reached a high value of 1.76 MV/cm³ in pulsed charged-discharged circuit.     

Preparation and electrical properties of Bi2Zn2/3Nb4/3O7 thin films deposited at room temperature for embedded capacitor applications

Bi₂Zn_2/3Nb_4/3O₇ thin films were deposited at room temperature on Pt/Ti/SiO₂/Si(1 0 0) and polymer-based copper clad laminate (CCL) substrates by pulsed laser deposition. Bi₂Zn_2/3Nb_4/3O₇ thin films were deposited in situ with no intentional heating under an oxygen pressure of 4 Pa and then post-annealed at 150 °C for 20 min. It was found that the films are still amorphous in nature, which was confirmed by the XRD analysis. It has been shown that the surface roughness of the substrates has a significant influence on the electrical properties of the dielectric films, especially on the leakage current. Bi₂Zn_2/3Nb_4/3O₇ thin films deposited on Pt/Ti/SiO₂/Si(1 0 0) substrates exhibit superior dielectric characteristics. The dielectric constant and loss tangent are 59.8 and 0.008 at 10 kHz, respectively. Leakage current density is 2.5 × 10^?7 A/cm² at an applied electric field of 400 kV/cm. Bi₂Zn_2/3Nb_4/3O₇ thin films deposited on CCL substrates exhibit the dielectric constant of 60 and loss tangent of 0.018, respectively. Leakage current density is less than 1 × 10^?6 A/cm² at 200 kV/cm.     

Improvement of energy density in SrTiO3 film capacitor via self-repairing behavior

Self-repairing behavior of SrTiO₃ film capacitor was explored to improve the energy density. With Au and Al being deposited on SrTiO₃ thin films as top electrode, the breakdown processes were investigated by a real-time optical microscope system. A high electric field of the electrode edge attributed to edge effect provided the “trigger factor” for the self-repairing behavior. Absorbed water not only provided “mobile phase” for self-repairing process which significantly enhanced breakdown strength but also, and equally important, it supplied additional polarization charges to raise dielectric constant. As a result of the concurrent increase in E_b and ε_r, a higher energy density of 15.7 J/cm³ is achieved. A leakage current platform was observed in the self-repairing process and the thickness of a new layer Al₂O₃ film generated from self-repairing process was estimated according to Ohm's law and breakdown strength. Using relative humidity dependence of breakdown voltage, the maximum breakdown field was explored to realize the optimum self-repairing capability.     

Enhanced electrocaloric effect and energy-storage performance in PBLZT films with various Ba2+ content

(100)-oriented Pb_(0.90−x)Ba_xLa_0.10Zr_0.90Ti_0.10O₃ (x=0, 0.02, 0.05 and 0.11) antiferroelectric thick films were deposited on LaNiO₃/Si (100) substrates by the sol-gel process. The influences of Ba²⁺ content on the dielectric properties, electrocaloric effect (ECE), energy-storage performance and leakage current were systematically investigated. With Ba²⁺ content increasing, the temperature (T_m) corresponding to the maximum dielectric constant of the thick films was decreased, while their diffuseness was increased. The maximum ECE ∆T=18.1 °C was obtained in the thick film with x=0.05 at room temperature under ∆E=700 kV/cm. The maximum energy storage density of 42.3 J/cm³ and the corresponding efficiency of 68% was achieved in the film with x=0.11, companied by a power density of 0.53 MW/cm³, due to its high breakdown strength. In addition, a small leakage current density (<10⁻⁵ A/cm²) were attained in these films at room temperature. In conclusion, we believe that this kind of antiferroelctric thick film is a potential candidate for applications in solid cooling devices and the energy-storage systems.