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Improving energy storage density and efficiency is the ultimate goal of dielectric materials used in ceramic capacitors. Among different dielectric materials, dielectrics in thin film state own superior energy performances due to less defects compared with ceramic. Herein, we report an optimized lead-free Zr-modified BiMg0.5Zr0.04Tix-0.04O3 composition with enhanced energy storage behavior via microstructural engineering. Rapid annealing can result in poorly crystallization in the film matrix confirmed by grazing incident X-ray diffraction GIXRD. The excess Ti source can effectively increase polarization and dielectric breakdown till to 97.0 μC/cm2 and 3403 kV/cm at x = 0.775, respectively. The optimized energy properties can be achieved at x = 0.775 with a high recoverable energy storage density Wreco of 87.8 J/cm3 and an efficiency η of 50%, indicative of excellent stability of storing electricity for the applications of pulse power electronics.

In this study, the intermediate rare-earth oxide Gd2O3 (Gd) was substituted in different amounts (x = 0.2–2 mol%) for the formulation of BaTi1-xGdxO3-x/2 (BTGx) dielectric materials. The effect of B-site substitution was confirmed by the additional Raman active A1g octahedral peak at ~835cm-1 strengthened at x ≥ 0.4 mol%. Additionally, properties of 0.9BTG0.007-0.1BA dielectric ceramics were analysed based on the influence of various processing methods as a function of sintering temperature. The focal samples were labelled Method-A (direct-mix) and Method-B (indirect-mix). As the sintering temperature (1075–1200 °C) increased, the 1 kHz response of the e–T curves of Method-A samples transformed from a single peak to broad-narrow double peaks of high dielectric loss tangent (tan δ). Nonetheless, samples of Method-B possessed a clearly defined transmission electron microscopy (TEM) core-shell structure, flattened double-peak e-T curves, optimised dielectric properties (e = ~1563–1851 and tan δ

In this work, Mn modified 0.94Bi0.5Na0.5TiO3-0.06BaTiO3 thin films (abbreviation for BNT-BT-Mnx) are prepared on Pt/Ti/SiO2/Si substrate via sol-gel and spin-coating. The influences of Mn dopant on the microstructural characteristics, dielectric and energy storage performances are studied systematically. It is found that by incorporating the Mn into BNT-BT, the breakdown strength and maximum polarization are enhanced dramatically, leading to the giant energy storage density of 54 J/cm3, with high permittivity 355 at 1 kHz. Moreover, the dominant leakage conduction mechanisms of the thin films are studied by linear fitting method, revealing that the leakage current mechanism of BNT-BT-Mnx films transforms from space-charge-limited conduction (SCLC) to Schottky emission as the increasing of electric field. The excellent energy storage density as well as dielectric properties suggest that BNT-BT-Mn6 thin film might be an attractive lead-free material for energy storage devices.

[(0.12BiAlO3-0.88BaTiO3)+0.5 wt%Nb2O5]+x wt.% B–Al–Si glass ceramics (x = 0, 1, 2, and 4) were prepared by solid-state method. The effects of B–Al–Si glass additive on microstructural and electrical properties were investigated. After the adding of B–Al–Si glass, quartz appeared as a new impurity phase and the average grain size of the samples decreased (from 540 nm to 330 nm). All the samples satisfy the EIA X8R specification, meanwhile, the breakdown strength (BDS) increased (from 17 kV/mm to 29 kV/mm) with the rising glass content. The ratios of relaxation time of grain boundary to grain (τgb/τg) of the ceramics at 460 °C were calculated according to the complex impedance data. It is found that decreased value of τgb/τg suggests a weakened interfacial polarization effect after B–Al–Si glass addition, which is beneficial to the BDS performance of ceramics.

The solid-state sintering route was employed for the production of (1-x)Bi2(Li0.5Ta1.5)O7-xTiO2 (x = 0, 0.02, 0.04, 0.06, 0.08) ceramics. The phase, microstructure and microwave dielectric properties of each ceramic composition were determined via X-ray diffraction, scanning electron microscopy and Haki Colmon resonator technique, respectively. The dielectric constant, tan δ and AC conductivity were also determined for the composition of x = 0.04. The TiO2 addition developed new phases of Bi3Ti4O12 and Bi3TaTiO9 for x = 0.04 along with Bi2(Li0.5Ta1.5)O7 phase which disappeared for x = 0.08. The τf of Bi2(Li0.5Ta1.5)O7 was tuned through zero by TiO2 addition and good microwave dielectric properties er~67.2, Qufo13,767 GHz and τf ~ −1.45 ppm/°C can be obtained for the composition of x = 0.04 sintered at 1050 °C for 2 h. This ceramic composition is a suitable candidate for 5G cellular base station resonator application.

Nb-containing antiferroelectric materials have recently attracted great research interest as energy storage materials for pulsed power capacitors due to their extraordinary energy storage performances. In this case, the optimization of the energy storage performance is obtained by a compositional modulation of NaNbO3-Bi(Zn2/3Nb1/3)O3 bulk ceramics. An optimal energy performance can be obtained with a composition of 0.85NaNbO3-0.15Bi(Zn2/3Nb1/3)O3, which is accompanied by a stable charge energy density in temperatures up to 150 °C owing to its relaxor characteristics and excellent cycling stability after 105 cycles. This work further broadens the scope of NaNbO3-based ceramic applications in the area of pulsed power sources.

Annealing temperature is a key element affecting the electrical properties and microstructure of dielectric thin films. In this case, BiAlO3 (BA) thin films were spin-coated on the Pt/Ti/SiO2/Si(100) substrates by sol-gel method and annealed at the temperature ranging from 450 °C to 550 °C. Then the influences of annealing temperatures on the microstructure, dielectric breakdown, and ferroelectric polarization of BiAlO3 thin films were studied. A optimal recoverable energy storage density (Wreco) of 31.1 J/cm3 and efficiency of 82.2% were achieved for the BA thin films annealed at 500 °C due to the ultrahigh dielectric breakdown strength (BDS) of 3535.7 kV/cm. This study offers a new paradigm for developing high-performance lead-free dielectric materials, which can largely extend the energy storage application of Bi-base perovskite materials.

0.5Bi 0·5 Na 0·5 TiO 3 -0.5SrTiO 3 -x wt% MgO (x = 0, 0.5, 1.0, 1.5, 2.0, 3.0) ceramics were fabricated via solid-state method. The effect of MgO doped on energy storage properties, dielectric performance, phase structure and microstructures of 0.5Bi 0·5 Na 0·5 TiO 3 -0.5SrTiO 3 (BNST) ceramics were studied systemically. The Mg 2+ substituted Ti 4+ site in BNST, which was confirmed by X-ray diffraction (XRD) result. The scanning electron microscope (SEM) images show that all the ceramic samples exhibit uniform and compact morphologies. The temperature dependent permittivity exhibits frequency dispersion, indicating that the ceramic samples are typical relaxor ferroelectrics. It was found that MgO doped BNST can significant improve the breakdown strength (E b ) of samples from 109 kV/cm to 227 kV/cm, which results in a great enhancement on energy storage density. The sample of x = 3.0 has the largest energy storage density (2.17 J/cm 3 ), which is twice as much as the BNST. Consequently, we consider that MgO-doped BNST ceramics are able to be a promising candidate in the field of pulsed-power devices.

In this work, the phase structure of BaTiO3 nanopowders produced by the alkoxide-hydroxide and the hydrothermal method, respectively, was systemically investigated. BaTiO3 nanopowders with cubic phase produced by the alkoxide-hydroxide method could transform to tetragonal phase when heated to about 1100 °C. Cubic to tetragonal phase transformation behavior of BaTiO3 nanopowders coated with 0.3BZT-0.7BT or 0.03Nb2O5-0.01Co2O3 was studied. The internal stress within core-shell structure was proposed to explain the BaTiO3 phase transformation behaviors. The mismatch of thermal expansion coefficient between core and shell plays a crucial role in cubic to tetragonal phase transformation of BaTiO3. By tuning the composition of shell and the ratio of the shell to the core, the cubic BaTiO3 core can transform to tetragonal phase successfully after sintering at 1100 °C in BaTiO3 based ceramics with core-shell structure and it is mainly resulted by the reduced internal stress between the shell and core.

The fine-grained silica-coated Ba0.3Sr0.7TiO3 (BST) ceramics were prepared by conventional solid-phase sintering method, the size of matrix materials which were produced by oxalate co-prepared method is about 100 nm. With the increase of the content silica, the grain size of ceramic dropped from 2 µm (pure BST) to 300 nm (Ba0.3Sr0.7TiO3-3 wt% SiO2) and the polarization of ceramic decreased under the same applied electric field, but the energy storage efficiency increased significantly. At the same time, the dielectric breakdown strength (BDS) increased significantly with the decrease of grain size and the addition of SiO2. For Ba0.3Sr0.7TiO3-3 wt% SiO2 ceramic, due to the small grain size, the BDS increased from 130 kV/cm to 380 kV/cm, its discharge energy storage density is 1.52 J/cm3 while the energy storage efficiency reaches 82.2%. The discharge energy density of the Ba0.3Sr0.7TiO3-3 wt% SiO2 ceramic increased to 3.3 times than that of pure Ba0.3Sr0.7TiO3 ceramic.

SrTiO3/BaTiO3 (ST/BT) thin-film heterostructure was deposited on Pt/Ti/SiO2/Si(100) substrate by spin-coating. X-ray diffraction pattern shows that the heterostructure is a perovskite structure composed of ST and BT without any impurity peaks. The dielectric constant and loss of the heterostructure at 10 kHz are 704 and 0.024, respectively. The electric-field dependence of dielectric response was investigated and the tunability of the sample under 200 kV/cm applied field is 21.5%. Compared with pure ST thin film, the polarization-electric field loops of ST/BT heterostructure display high polarization and good symmetry, which could be attributed to the introduction of BT with high dielectric constant and inhibition of the potential pitfalls movement for high barrier at ST/BT interface. Moreover, the heterostructure demonstrates photoconductivity behavior with 405 nm light illumination. The results indicate that ST/BT heterostructure is a potential material in application as multifunctional photoelectric devices.

Sr0.99Ce0.01Ti1-xO3 (SCT, x = 0, ± 0.0025, ± 0.0050, 0.0075) ceramics were prepared by solid state reaction methods and sintered in air atmosphere at different temperatures, with a soaking time of 2 h. The dielectric properties of all samples presented excellent temperature independence over a broad temperature range from 25 to 330 ℃ and frequency independence between 10 kHz and 1 MHz. Sr0.99Ce0.01Ti0.9925O3 (SCT0.9925) ceramics sintered in air atmosphere exhibited a high permittivity (~5400) and a low dielectric loss (~0.01) measured at room temperature and 1 kHz. XPS and complex impedance spectroscopy analysis confirmed that the high permittivity and low dielectric loss were attributed to the fully ionized oxygen vacancies and giant defect-dipoles in Ti-deficient samples. However, a higher dielectric loss of Ti-rich samples is owing to the destruction of giant defect dipoles, in which highly localized electrons were transformed into hopping electrons.

We explored the phase structure, microstructure, dielectric and energy storage properties of MgO-modified strontium barium niobate Sr0.7Ba0.3Nb2O6-xwt%MgO (SBNMx; x = 0–5) ceramics fabricated via conventional solid-state sintering precess. X-ray diffraction analysis indicates Mg2+ incorporates into lattice at x = 0.5 and secondary phases come into formation for samples at x ≥ 1, which results in the decrease of dielectric constant. There is also significant reduction of dielectric loss up to 0.002. Compared with pure SBN ceramics, the grain size of SBNMx ceramics becomes denser and more uniform, moreover, the dielectric breakdown strength shows increasing trend from 137 kV/cm to 226 kV/cm, which is in favor of the energy storage. SBNM0.5 ceramics presents the optimal energy storage performance: energy storage density of 0.93 J/cm3 and energy storage efficiency of 89.4% at 157 kV/cm, indicating that SBNM ceramics are prospective candidates for high voltage capacitor applications.

BaTi1-xCaxO3-x [BTC100x] ceramics were synthesized via solid-state reaction method. Effect of Ca substitution on the structure, electrical and dielectric properties of BTC100x ceramics was systematically investigated. Calcined BTC100x powders were in tetragonal phase when x ≤ 0.01, whereas transformed to cubic at x > 0.01. Additionally, the diffraction peak (200) shifted to lower angles with increasing x, indicating increased unit cell volume. Meanwhile, Ba0.97Ca0.03TiO3 [BC3T] ceramic was prepared and studied, to compare with BaTi0.97Ca0.03O2.97 (BTC3). It was found that pure BaTiO3 [BT] and BC3T ceramics had the similar structural and dielectric properties, whereas BTC3 ceramic showed much difference，XRD patterns, Raman spectrum, impedance spectra and dielectric-temperature spectra provided strong evidence of Ca2+ substitution at Ti site in BT lattice. Finally, BTC100x ceramics were produced and dielectric properties were investigated. With increasing x, the Curie temperature decreased from 128 °C (BT) to 42 °C (BTC5).

Ba0.7Sr0.3FexTi1−xO3 (x = 0, 0.004, 0.008, 0.01, 0.015) ceramic thin films were prepared on platinized silicon wafers via sol-gel deposition method. Significant enhancement of grain size and dielectric constant were observed when x

Dielectrics for energy storage devices should commonly achieve the requirement of high permittivity, large breakdown strength, and large polarization when used in harsh working environments. A question is gradually raised about permittivity/polarization/breakdown strength in a dielectric for high voltage applications which one is more conducive to energy storage performances. Here, an attempt has been made to investigate the effect of high permittivity on the energy performances of dielectric materials in order to provide a viable option for high voltage devices. High values of dielectric permittivity (1300–7400) combined with low dielectric loss (

The microwave dielectric properties and microstructure of the new ceramic system (1 − x )Mg(Ti 0.95 Sn 0.05 )O 3 – x CaTiO 3 (0.02 ≤ x ≤ 0.08) prepared via a mixed-oxide route were investigated. To attain a temperature-stable material, CaTiO 3 was added to Mg(Ti 0.95 Sn 0.05 )O 3 as a temperature coefficient of resonant frequency ( τ f ) compensator. The compositions with 0.02 ≤ x ≤ 0.08 resulted in a mixture of two phases, Mg(Ti 0.95 Sn 0.05 )O 3 and CaTiO 3 , as confirmed by X-ray diffraction and energy-dispersive X-ray spectroscopic analyses. The values of the dielectric constant ( e r ) and the τ f of the ceramics were found to increase, and the unloaded quality factor ( Q u f o ) was found to decrease with increasing x values (i.e., increasing CaTiO 3 content). Excellent microwave dielectric properties of e r ≈ 21.5, Q u f o ≈ 112,500 GHz (at 9 GHz), and τ f ≈ 1.1 ppm/°C were attained for the 0.94{Mg(Ti 0.95 Sn 0.05 )O 3 }–0.06CaTiO 3 ceramic sintered at 1375 °C for 4 h.

In this paper, a core-shell structure, where the BaTiO 3 (BT) particles were coated with 0.25Bi(Zn 1/2 Ti 1/2 )O 3 -0.75BaTiO 3 [BT@x(0.25BZT-0.75BT)] by sol-gel method, was fabricated and confirmed by transmission electron microscopy (TEM). The impedance data of BT, 0.25BZT-0.75BT and BT@x(0.25BZT-0.75BT) (x=0.5–1.0) ceramics was collected and fitted by different equivalent circuits. The core and shell regions of BT@x(0.25BZT-0.75BT) (x=0.5–1.0) ceramics can be separated in complex impedance plots (fitted by a 4RC equivalent circuit), according to the activation energies of BT and 0.25BZT-0.75BT. The calculated activation energy of the core part in BT@x(0.25BZT-0.75BT) ceramics is relatively stable, being closer to the activation energy (0.86 eV) of BT, while the activation energy of the shell was found to increase from 0.28 eV to 0.53 eV with increasing the shell thickness. The average core/shell ratio (d gc /d gs ) for BT@0.8(0.25BZT-0.75BT) ceramics was found to be on the order of 7.26, calculated by a modified two-layer dielectric model. In addition, Lichtenecker formula was used to simulate the dielectric constant of BT@0.8(0.25BZT-0.75BT) ceramics at room temperature and the simulated results are in agreement with the measured values.

xBa 0.7 Sr 0.3 TiO 3 -SrTiO 3 (BST-ST) multilayer ceramics with different BST layers (x=1, 3, 5) were designed and fabricated by lamination of Ba 0.7 Sr 0.3 TiO 3 (BST) and SrTiO 3 (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 ( 3 . These results indicate that BST-ST multilayer ceramics can be a favorable candidate for dielectric capacitor applications.

Mg 1−x Zn x SiO 3 (x=0–0.3) ceramics were successfully synthesized by conventional solid-state methods and characterized by scanning electron microscopy, dispersive X-ray spectroscopy, and X-ray diffraction. The microstructures and microwave dielectric properties of Mg 1−x Zn x SiO 3 ceramics were systematically investigated. The lattice parameters of the samples with different Zn 2+ contents were analyzed. When the Zn 2+ content was increased from 0 to 0.15, the Q u f o of the sample increased from 103,453 GHz to a maximum 138,481 GHz. This also resulted in a significant lowering in the sintering temperature (90 °C). Monoclinic structured Mg 0.85 Zn 0.15 SiO 3 was detected without any secondary phase. In this study, a new combination of microwave dielectric properties (e r ∼8.05, Q u f o ∼138,481 GHz, τ f ∼−14 ppm/°C) was achieved for Mg 0.85 Zn 0.15 SiO 3 sample sintered at 1360 °C for 9 h. The prepared material with remarkable useful dielectric properties can be used for millimeter-wave applications.

The Ba x Sr 0.97−x Sm 0.02 TiO 3 (x=0–0.4) ceramics in different sintering atmosphere were prepared by conventional solid-state reaction methods. The effect of different atmosphere on the dielectric properties of Ba x Sr 0.97−x Sm 0.02 TiO 3 ceramics was investigated. The giant permittivity was obtained for Ba x Sr 0.97−x Sm 0.02 TiO 3 ceramics sintered in nitrogen especially for x=0.2, which exhibited a weak temperature- and frequency- dependent giant permittivity (>10 4 ) as well as a low dielectric loss (mostly 4+ ·e - V o . . - e·Ti 4+ ] generated by the fully ionized oxygen vacancies and Ti 3+ ions, while the defect dipoles ( V Sr , , − V o . . ) and interfacial polarization caused the dielectric relaxation of the ceramics sintered in air or O 2 .

Piezoelectric properties and thermal stability of tetragonal-structured (Ba 0.838 Ca 0.162 )(Ti 0.908−x Mn x Zr 0.092 )O 3 (0.46BZT–0.54BCTMn) compositions away from morphotropic phase boundary (MPB) were investigated. The results demonstrated that the addition of small amounts of Mn did not cause a remarkable change in crystal structure, but resulted in an evident evolution in piezoelectric properties and thermal stability. Mn could induce combinatory hard and soft piezoelectric characteristics due to aliovalent substitutions and improve thermal stability. The optimal electrical properties were obtained in the modified composition at x=0.006 with piezoelectric constant d 33 =410 pC/N, planar electromechanical coupling factor k p =0.40, mechanical quality factor Q m =150, remnant polarization P r =14.1 μC/cm 2 , coercive field E c =4.44 kV/cm and a high Curie temperature T c ~99 °C, respectively. It can be expected that the improved piezoelectric material can be a promising candidate for lead-free piezoelectric applications.

SiO 2 -added barium strontium titanate ceramics Ba 0.4 Sr 0.6 TiO 3 - x wt%SiO 2 ( x =0, 0.5, 1, 3, BSTS x ) were prepared via a traditional solid state reaction method. The effect of SiO 2 additive on the microstructure, dielectric response and energy storage properties was investigated. The results confirmed that with the increase of SiO 2 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 SiO 2 additive led to improve the breakdown strength, further increase of SiO 2 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/cm 3 and energy storage efficiency of 79% at 134 kV/cm.

SrSnxTi(1−x)O3 (x=0, 0.01, 0.03, 0.05, 0.07) dielectric ceramics were fabricated by the solid state reaction method. Significant refinement of grain size and improved resistivity were observed with the addition of Sn, accounting for effectively enhanced dielectric breakdown strength, beneficial for the energy storage applications. Impedance analysis was employed to calculate the conductivities of grain and grain boundary and resistance ratios (Rgb/Rg) of grain boundary to grain. The grain boundary effect was believed to dominate the modified macroscopic performance, which was confirmed by the complex impedance analysis. The optimal properties were achieved for samples with x=0.05, exhibiting a charge energy density of 1.1 J/cm3 and an energy efficiency of 87%.

The typical “core–shell” structure in BT ceramics can easily obtain double dielectric anomalies, which greatly improve the dielectric temperature stability for multilayer ceramic capacitors. In this paper, BaTiO3 particles were coated with 0.3BiAlO3–0.7BaTiO3 shell [xBT@(0.3BA–0.7BT)] by a sol–gel method. Core–shell structure was proved to exist in ceramic grains by transmission electron microscopy (TEM) and energy-dispersive spectroscopy (EDS). High-temperature X9R dielectrics were obtained when x=0.3 and 0.2, with a high dielectric constant (~1200) and low dielectric loss (

Sr 0.9775 Sm 0.015 TiO 3 ceramics with giant permittivity of about 40,000 and low dielectric loss of 0.0068 measured at 25 °C and 1 kHz were obtained by sintering the ceramics in N 2 at 1500 °C. The surface structure was analyzed by XPS measurement, which implied that a large number of Ti 3+ ions existed in the Sr 0.9775 Sm 0.015 TiO 3 ceramics sintered in N 2 . The results indicated that making the oxygen vacancies fully ionized by N 2 sintering could increase the permittivity and decrease the dielectric loss effectively.

The effects of TiO 2 additives on microstructure and microwave dielectric properties of α -CaSiO 3 –2 wt%Al 2 O 3 ceramics have been investigated in detail. Specifically, the TiO 2 addition results in the presence of two distinct phases, e.g. CaTiO 3 and CaTiSiO 5 , which can inhibit the growth of α -CaSiO 3 grains by surrounding their boundaries and also improve the bulk density of α -CaSiO 3 –2 wt%Al 2 O 3 ceramics. However, the TiO 2 addition undermines the microwave dielectric properties of the title ceramics because the derived phases of CaTiO 3 and CaTiSiO 5 have poor quality factor. The τ f value is strongly correlated to the compositions and can be controlled through the compositional ratio. The α -CaSiO 3 –2 wt%Al 2 O 3 ceramics containing 2.5 wt% of TiO 2 sintered at 1250 °C showed excellent microwave dielectric properties (e r =7.88, Q × f =24,412 GHz and τ f =−0.52 ppm/°C).

MgO-doped 0.97BaTiO 3 –0.03BiYO 3 (0.97BT–0.03BY) polycrystalline ceramics were prepared by the solid-state sintering method. Then the structural, dielectric and resistant properties were investigated as functions of MgO addition. Microstructure was studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive spectrometry (EDS). The results show that Bi 3+ , Y 3+ and Mg 2+ ions exhibit nonuniform distribution behavior in BT–BY ceramics, demonstrating the existence of a “core–shell” structure, which plays important roles in the capacitance-temperature characteristics, where 0.97BT–0.03BY with the addition 2.2–2.8 at% MgO meets the Electronic Industries Association (EIA) X8R (−55 to 150 °C, ΔC / C 25 °C =±15% or less) specification. Moreover, the fine-grained samples with core–shell structure show much higher bulk resistance than the coarse-grained samples over the studied temperature range, which is attributed to the higher proportion of grain boundaries and the lower concentration of the effective acceptor.

SrTiO 3 ceramics with trace amounts of ZrO 2 additives were prepared via the solid state reaction route. The effects of ZrO 2 concentrations on microstructures, dielectric and energy storage properties of SrTiO 3 ceramics were investigated. The grain size of the ceramics decreases with increasing ZrO 2 concentration. Dielectric relaxation behaviors were observed in dielectric loss versus temperature plots and studied by the measurements of the activation energies, which indicated the behaviors were due to the doubly ionized oxygen vacancies and the space-charge polarization. An energy density of 1.62 J/cm 3 and a breakdown strength of 289 kV/cm were achieved for SrTiO 3 ceramics with 0.4 mol% ZrO 2 addition, which were higher than those of pure SrTiO 3 ceramics.

Effects of nonstoichiometric SrTiO 3 ceramics have been investigated in the range of Sr/Ti=0.994–1.004. A cubic perovskite structure is maintained at all compositions without any secondary phase. Grain size increases at the beginning and then decreases with increasing Sr/Ti ratio. The highest breakdown strength and energy density are obtained at Sr/Ti=0.996, 283 kV/cm and 1.21 J/cm 3 , respectively, which are higher than that of stoichiometric SrTiO 3 ceramic (210 kV/cm of breakdown strength, 0.7 J/cm 3 of energy density). Sr/Ti>1 ST ceramics are prone to semi-conductivity process. Among them, the ST ceramic at Sr/Ti=1.004 has the highest permittivity, 2455.

Nb2O5 and Nb–Co doped 0.85BaTiO3–0.15Bi(Mg1/2Ti1/2)O3 (0.85BT–0.15BMT) ceramics were investigated. From XRD patterns, undesired phase was observed when the (Nb2O5/Nb-Co) doping levels exceed 3 wt.%/2 wt.%, giving rise to the deteriorate dielectric constant. The 0.85BT–0.15BMT ceramics doped with 2 wt.%Nb2O5 was found to possess a moderate dielectric constant (ɛ ∼ 1000) and low dielectric loss (tan δ = 0.9%) at room temperature and 1 kHz, showing flat dielectric behavior over the temperature range from −55 to 155 °C. It was found that the formation of core–shell structure in the BT based ceramics is controlled by the doping sequence of Nb- and Bi-oxides.