Pure Ba0 Research Articles

Structural Evolution, Dielectric, Ferroelectric and Thermal Properties of Pristine and (Sr, Mn) Co-doped BaTiO3

Nanocrystalline specimen of pure BaTiO3 (BTO) and Ba0.9Sr0.1Ti0.95Mn0.05O3 (BSTMO5) has been synthesized through solid state route. XRD patterns reveal uni-phase tetragonal configuration with P4mm space group. The crystallite size and strain have been evaluated by fitting the data with Williamson-Hall equation. Raman spectra are consistent with the tetragonal phase of BTO. Colossal value of dielectric constant is observed for BTO samples. The temperature-dependent P-E loops reveal highest value of polarization at 323K. Differential thermal analysis (DTA) is used to evaluate the specific heat (Cp) of the samples. Doping with (Sr, Mn) raises the Curie temperature hence enhancing the temperature stability of BTO. It can broaden the temperature range over which the material exhibits desirable ferroelectric and dielectric properties. This improved stability along with high dielectric permittivity is advantageous for applications that require operation over a wide temperature range. The band gap enhanced for BSTMO5 making it suitable for usage in optoelectronic devices.

Metal Particle Composite Hardening in Ba0.85Ca0.15Ti0.90Zr0.10O3 Piezoceramics

AbstractHard‐type piezoceramics are key materials in high‐power transducers and transformers. Acceptor doping is the most widely used piezoelectric hardening approach, but the mobility of oxygen vacancies at large electric fields or at high temperatures inevitably leads to the deterioration of hardening performance. The present study proposes a new hardening method associated with intragranular metal particles for achieving strong pinning of ferroelectric domain walls. Highly effective piezoelectric hardening via intragranular Ag particles in Ba0.85Ca0.15Ti0.90Zr0.10O3 ceramic is realized, where the mechanical quality factor Qm and the coercive field Ec increase by 170% and 53%, respectively. The Ba0.85Ca0.15Ti0.90Zr0.10O3/0.10Ag sample features a larger high‐power mechanical quality factor than the pure Ba0.85Ca0.15Ti0.90Zr0.10O3. Moreover, the piezoelectric properties (d31 and k31) of the Ba0.85Ca0.15Ti0.90Zr0.10O3/0.10Ag sample show exceptional stability with the increase in vibration velocity. This composite approach of introducing metal particles can be considered as a generic hardening method and can be extended to other ferroelectric systems.

Effects of raw materials on nonhydrolytic sol-gel synthesis of Ba0.6Sr0.4TiO3

The effects of raw materials on the nonhydrolytic sol-gel synthesis of Ba0.6Sr0.4TiO3 were systematically studied in this work. The samples were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM). Ba(CH3COO)2, Sr(CH3COO)2, BaCO3 and SrCO3 can undergo deesterification substitution reaction with Ti(OC4H9)4 to synthesize Ba0.6Sr0.4TiO3 phase. Sample taking Ba(CH3COO)2 and Sr(CH3COO)2 as barium and strontium source has better Ba0.6Sr0.4TiO3 synthesis results than that of samples using BaCO3 or SrCO3. Ba0.6Sr0.4TiO3 phase can not be synthesized at low temperature taking BaCl2, SrCl2 and TiOSO4 as barium, strontium or titanium source due to their strong ionic bonding. TiCl4 undergoes an alcoholysis reaction with (oxygen donor) alcohol to form a multimolecular association structure and solvated complex chlorotitanium alkoxide, which reduces the possibility of a deesterification polycondensation reaction. The Ba0.6Sr0.4TiO3 phase cannot be synthesized at low temperatures when CH3CH2OH or C3H7OH is used as the solvent. The synthesis of Ba0.6Sr0.4TiO3 is insufficient because of the coordination ability and solvation effect when CH3COOH is used as the solvent. The synthesis of Ba0.6Sr0.4TiO3 is the best when Ba(CH3COO)2, Sr(CH3COO)2, Ti(OC4H9)4 and glycerol (C3H8O3) are used as the barium source, strontium source, titanium source and solvent, respectively. Pure Ba0.6Sr0.4TiO3 phase with a particle size of 17–43 nm and high dispersion is synthesized when the molar ratio of barium-strontium-titanium is 0.6:0.4:1.2.

Effect of Ni Substitution on Structural, Dielectric, and Ferroelectric Properties and Variation in Magnetocapacitance of Single-Phase Ba0.7Pb0.3TiO3 Ceramic

The present study demonstrates the influence of Ni substitution on the structural, dielectric, and ferroelectric properties of single-phase Pb-doped BaTiO3, that is, Ba0.7Pb0.3TiO3 (BPT) ceramic, and variations in the magnetocapacitance. The hydroxide co-precipitation method was employed to fabricate single-phase Pb-doped BaTiO3 and Ni-substituted Ba0.7Pb0.3TiO3, as Ba0.7Pb0.3TiO3-(x)Ni for x = 0.05, 0.1, and 0.15. Rietveld refinement reflects the single-phase tetragonal crystal structure of pure Ba0.7Pb0.3TiO3 and at higher Ni concentrations, the detection of rhombohedral crystal symmetry of the NiO phase confirms the biphasic structure of the composite. The ferroelectric-paraelectric transition temperature decreased from 274 °C for pure Ba0.7Pb0.3TiO3 to 162 °C for the composite with a higher Ni concentration of x = 0.15. A drastic change in the typical ferroelectric (P-E) loop of Ba0.7Pb0.3TiO3 was observed with the substitution of Ni. The composite with a higher concentration had the highest value of the magnetodielectric coupling coefficient, MD (%) = −2.86. This study reflects an easy and useful approach to achieve two-order parameter coupling with doping of acceptor ions in the ferroelectric phase. This kind of material substantially plays a vital role in the advanced electromagnetic devices for futuristic applications.

Barium calcium titanate @carbon hybrid materials for high-efficiency room-temperature pyrocatalysis

In this work, a significant enhancement of pyrocatalysis is found in barium calcium titanate @carbon (Ba0.8Ca0.2TiO3@C) hybrid nanofibers hydrothermally synthesized and designed to decompose rhodamine B (RhB) dye. The pure Ba0.8Ca0.2TiO3 can decompose the RhB dye at 30–60 °C cold-hot cycles with a final decomposition ratio of 31.3%. As the content of C mixed in Ba0.8Ca0.2TiO3 gradually increases from 0 to 5 wt%, the decomposition ratio of RhB first increases and then decreases, with the highest decomposition ratio of 76.6%, when the content of C is 3 wt%. The enhancement of pyrocatalytic activity could be attributed to the fact that the presence of C accelerates the carrier mobility and impedes the free charges recombination in the pyrocatalysis process. With the enhanced pyrocatalytic performance, Ba0.8Ca0.2TiO3@C hybrid nanofibers have tremendous potential for the alleviation of dye wastewater pollution through utilizing alternative cold-hot energy variation.

Silver-Doped BaSrTiO₃ Nanocomposite: Synthesis, Characterization, Antibacterial and Photocatalytic Activities.

In this research, strontium titanate (SrTiO₃), barium titanate (BaTiO₃), barium strontium titanate (BaSrTiO₃), and Ag-doped BaSrTiO₃ nanocomposites with different Ag contents were fabricated using the sol-gel chemical route. The prepared samples were characterized by several techniques including scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), differential reflectance spectroscopy (DRS), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), inductively coupled plasma spectroscopy (ICP), and Brunauer-Emmett-Teller (BET) measurement. The EDS results indicated that the synthesized nanoparticles had a cube perovskite-like structure. The EDS and ICP results revealed that Ag was doped into the Ba0.5Sr0.5TiO₃ structure. The SEM and TEM images demonstrated that the particle size of 15 mol% Ag-doped Ba0.5Sr0.5TiO₃ was smaller than that of pure Ba0.5Sr0.5TiO₃ as confirmed by surface area results. The photocatalytic properties of undoped titanate samples and Ag-doped Ba0.5Sr0.5TiO₃ were studied by the photodecomposition of Eosin yellowish (EY) and methylene blue (MB) dyes. The results illustrated that the photodegradation efficiency of the Ag-doped Ba0.5Sr0.5TiO₃ was far higher than the undoped titanate sample, and the optimum Ag doping was 15 mol%. The antibacterial activities of pure Ba0.5Sr0.5TiO₃ and Ag-doped Ba0.5Sr0.5Ti0₃ were studied against Staphylococcus aureus as Gram-positive (+) and Pseudomonas aeruginosa and Escherichia coli as Gram-negative (-) bacteria. In comparison with the bare Ba0.5Sr0.5TiO₃ nanoparticles, the Ag-doped sample showed a significant enhancement in antibacterial activities against both Gram-negative and Gram-positive bacterial strains.

Magnetic properties, structural studies and microwave absorption performance of Ba0.5Sr0.5CuxZrxFe12-2xO19/Poly Ortho-Toluidine (X = 0.2,0.4, 0.6, 0.8) ceramic nanocomposites

Cu/Zr-doped barium strontium hexaferrite/poly (O-toluidine) nanocomposites (Ba0.5Sr0.5CuxZrxFe12-2xO19/POT) (BSCZH/POT) (X = 0.2, 0.4, 0.6, 0.8) were synthesized by the in-situ polymerization of O-toluidine in the presence of BSCZH as electromagnetic shields in the Ku-Band (12–18 GHz) frequency ranges. The Rietveld refinement, according to the X-ray diffraction analysis results, showed that the prepared samples possessed a single-phase with the space group of P63/mmc; also, the lattice parameter constant (a) was 5.898(Å) for the pure Ba0.5 Sr0.5 Fe12O19 nanoparticle (x = 0); further, the value of the lattice constant (a) was increased to 5.918(Å) for BSCZH (x = 0.8) with raising the concentration of the dopant. A decrement in the saturation magnetization of BSCZH/POT, as compared to BSCZH in the VSM analysis, indicated that the synthesized polymer was immobilized on the surface of hexaferrite nanoparticles. TEM analysis also demonstrated the core–shell structure of the nanocomposites, thus corroborating that the nanoparticles were coated via the in-situ polymerization of O-toluidine on the surface of nanoparticles. VNA analysis also revealed that the BSCZH/POT nanocomposite with the thickness of 2 mm had the highest microwave absorption of about 90% (the reflection loss value of −27.63 dB at 16.32 GHz) for BSCZH/POT (X = 0.2), as compared to the other samples in the Ku-Band (12–18 GHz) frequency ranges. The results, therefore, indicated that the newly synthesized nanocomposite could be used as an efficient EMI shield against electromagnetic pollution.

Microwave absorption studies of (Ba0.5Sr0.5Fe12O19)1-x/(NiFe2O4)x hard/soft ferrite nanocomposites

Magnetic nanocomposites consisting of barium strontium hexaferrite and nickel ferrite as the hard and the soft phases respectively (Ba0.5Sr0.5Fe12O19)1-x/(NiFe2O4)x with the compositions x = 0.1, 0.2, 0.3 and 0.4, were synthesized by a modified sol-gel technique using citric acid as the fuel. The as-synthesized material was heat treated at 1100 °C for 2 h. A 20% increase in the Ms was found in the ferrite nanocomposite with the addition of 10 wt% of NiFe2O4. Decrease in coercive field with increase in soft phase content was observed, attributing to the dominance of dipolar interaction over exchange interaction. There was no kink observed in the hysteresis loops of nanocomposites, confirming the single-phase behaviour. All the nanocomposites prepared by the modified sol-gel method exhibited good exchange coupling behaviour with Mr/Ms values of >0.5. All the prepared nanocomposites displayed excellent microwave absorption properties in the X-band region (8–12 GHz). The absorber thickness was maintained as 2.5 mm. Minimum reflection loss of −38.74 dB was attained for the composition (Ba0.5Sr0.5Fe12O19)0.6/(NiFe2O4)0.4, which is 47% higher than the pure Ba0.5Sr0.5Fe12O19.

Manipulating the ferroelectric, dielectric and photoluminescence performance of Ba0·77Ca0·23TiO3 ceramics through Pr3+ ions doping

The Pr3+-doped Ba0·77Ca0·23TiO3 ferroelectric ceramics, which were sintered by means of a high-temperature solid-state reaction technology, were prepared. The Rietveld X-ray diffraction refinement and Raman spectrum proved that the resultant compounds had tetragonal phase. With the addition of Pr3+ ions, the highest remanent polarization of the resultant ceramics was nearly two times higher than that of the pure Ba0·77Ca0·23TiO3 ceramics. With the aid of a theoretical calculation based on the temperature-dependent dielectric constant, it is found that the synthesized compounds pertained to the relaxor-like ferroelectrics. Furthermore, through the piezoresponse force microscopy technique, the effect of Pr3+ ions doping on the domain structure of the Ba0·77Ca0·23TiO3 ferroelectric ceramics was studied. Additionally, the prepared ferroelectric ceramics can exhibited the characteristic emissions of Pr3+ ions when excited by 450 nm light. The strongest emission intensity was achieved when the dopant content was 0.5 mol% and the dipole-quadrupole interaction contributed to the relevant concentration quenching mechanism.

Pyroelectric energy conversion using Ba0.85Sr0.15Zr0.1Ti0.9O3 ceramics and its cement-based composites

In this article, we focus on cement-binded Ba0.85Sr0.15Zr0.1Ti0.9O3 ceramics for pyroelectric applications. It was prepared with the Ba0.85Sr0.15Zr0.1Ti0.9O3-to-cement ratios of 85%:15% and 80%:20% by weight. In order to improve the effectiveness of thermal-to-electric energy conversion, the synchronized switch harvesting on inductor technique is experimentally tested on cement composites. Our experimental findings reveal that this concept based on synchronized switch harvesting on inductor can significantly increase the amount of power extracted from pyroelectric materials. Furthermore, the optimized power across 15% and 20% cement composites were found to be 7.2 and 6 nW, respectively, in series synchronized switch harvesting on inductor and 8.5 and 7 nW, respectively, in parallel synchronized switch harvesting on inductor. These values are significantly higher when compared with non-switched circuit for pyroelectric applications. Although, from the obtained results for the prepared composites, the power output is less when compared with pure Ba0.85Sr0.15Zr0.1Ti0.9O3, they have some advantages: these composites can be made without any sintering process and are compatible for structural applications.

Dielectric tunable properties of Ba0.5Sr0.5TiO3−Mg2TiO4−MgO composite ceramics prepared by spark plasma sintering

Ba0.5Sr0.5TiO3−Mg2TiO4−MgO composite ceramics were prepared by spark plasma sintering (SPS) technique and their phase composition, microstructures and dielectric tunable properties were studied. With increasing Mg2TiO4−MgO content, the dielectric peaks of Ba0.5Sr0.5TiO3−Mg2TiO4−MgO composite ceramics were broadened and suppressed. The tunability of Ba0.5Sr0.5TiO3−Mg2TiO4−MgO composite ceramics increased first and then decreased with the increase of Mg2TiO4−MgO content. For Mg2TiO4−MgO content ≤50 wt%, Ba0.5Sr0.5TiO3−Mg2TiO4−MgO composite ceramics showed higher tunability and lower permittivity than pure Ba0.5Sr0.5TiO3, which can be attributed to the suppression of the doping effect by SPS. The contradiction between reduced permittivity and enhanced tunability in ferroelectric-dielectric composites was resolved.

The Study of Microstructure, Dielectric and Multiferroic Properties of (1 − x) Co0.8Cu0.2Fe2O4-xBa0.6Sr0.4TiO3 Composites

Magnetoelectric multiferroic materials have attracted great attention due to their intriguing properties and potential applications. In this paper, (1 − x) Co0.8Cu0.2Fe2O4-xBa0.6Sr0.4TiO3 (x = 0, 0.4, 0.45, 0.475, 0.5, 0.525, 0.55, 1) composites were prepared by the conventional solid-state method combining with a sol–gel process. The effect of x on the microstructure, dielectric and multiferroic properties has been systematically investigated and discussed. The results confirm pure bi-phase Co0.8Cu0.2Fe2O4 and Ba0.6Sr0.4TiO3 composites except for slight impurity phases, which are indexed as BaCuO2/BaFe12O19. All the samples show uniform and relatively smooth surfaces with the mean grain size of ∼ 1.5 μm which decreases slightly with the increase of x, demonstrating the moderating effect of the ferroelectric phase on the grain size. The dielectric constant shows intense dependence on the components and the highest value is obtained when x = 0.525. The ferroelectric loops demonstrate that the coercive field and remnant polarization of the sample x = 0.525 are higher than other samples except for the pure Ba0.6Sr0.4TiO3 specimen at room temperature. The Co0.8Cu0.2Fe2O4 shows better magnetic properties and the performance of magnetization decreases with the decrease of Ba0.6Sr0.4TiO3; meanwhile, the impurity phase and inhomogeneous structure have certain influences on the magnetic properties.

Fine-grained silica-coated barium strontium titanate ceramics with high energy storage

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.

Structural evolution and electrical characteristics of Sn-doped Ba0.8Sr0.2TiO3 ceramics

(Ba0.8Sr0.2)(Ti1−xSnx)O3 (BSTS) perovskite structure ferroelectric ceramics with different compositions (x=0; 0.03; 0.05; 0.07; 0.10 and 0.20) were synthesized by a conventional high temperature solid-state reaction. X-ray diffraction (XRD) study allowed the identification of a pure solid solution with average tetragonal symmetry for x≤0.05 and cubic for x≥0.07 at room temperature (RT). Especially, for the composition x=0.05, a coexistence of tetragonal (P4mm) with dominating fraction close to 88.84% and cubic (Pm3¯m) (11.16%) phases was determined in powder by Rietveld refinement. The local structures of the BSTS samples were studied by Raman spectroscopy, which shows a small fraction of rhombohedral phases for Sn-rich compositions (x≥0.05) at RT. Dielectric analysis show a diffuse phase transition for x≤0.10, the dielectric permittivity become three time better than that of pure (Ba0.8Sr0.2) TiO3 and when x=0.20, the material change from normal ferroelectric to a typical relaxor ferroelectric. Macroscopic Polarization-field loops measured at RT illustrate a decreasing of the polarization at the maximum field of 3kV/mm from 14.31 to 1.35µC/cm2 confirming XRD and dielectric studies.

The effect of Cu2O nanoparticle dispersion on the thermoelectric properties of n-type skutterudites

We report the thermoelectric properties of Ba0.4Co4Sb12 and Sn0.4Ba0.4Co4Sb12 skutterudites dispersed with Cu2O nanoparticles. The samples were synthesized by ball milling and consolidated by spark plasma sintering. Dispersion of Cu2O is found to significantly influence the electrical resistivity and thermopower at high temperatures with a more pronounced effect on the electrical resistivity due to the energy filtering effect at the interface between Cu2O nanoparticles and a Ba0.4Co4Sb12 and Sn0.4Ba0.4Co4Sb12 matrix. At 573 K, the electrical resistivity of Ba0.4Co4Sb12 decreases from 5.01 × 10−5 Ωm to 2.98 × 10−5 Ωm upon dispersion of Cu2O. The dispersion of Cu2O reduces the thermal conductivity of the samples from 300 K and above by increasing the phonon scattering. The lowest observed thermal conductivity at 573 K is found to be 2.001 W mK−1 in Cu2O dispersed Ba0.4Co4Sb12 while it is 2.91 W mK−1 in the Ba0.4Co4Sb12 sample without Cu2O dispersion. Hence Cu2O dispersion plays a significant role in the thermoelectric properties and a maximum figure of merit (ZT ) ~ 0.92 is achieved in Cu2O dispersed Ba0.4Co4Sb12 at 573 K which is more than 200% compared to the pure Ba0.4Co4Sb12 sample. The results from nanoindentation experiments show that the Cu2O dispersed sample (Cu2O + Sn0.4Ba0.4Co4Sb11.6) has a higher reduced Young’s modulus (~139 GPa) than the pure Sn0.4Ba0.4Co4Sb11.6 sample (~128 GPa).

Modification of the structure and electrical properties of Ba0.95Ca0.05Zr0.1Ti0.9O3 ceramics by the doping of Mn ions

Pure and Mn-modified Ba0.95Ca0.05Zr0.1Ti0.9O3 ceramics were fabricated by the traditional solid state reaction technique. The influence of manganese and sintering temperature on structure, dielectric, ferroelectric properties of BCZT ceramics were investigated systematically. 1450 °C was the optimal sintering temperature for BCZT ceramics. Compared with undoped counterparts, 1.2 mol% Mn-modified ceramics showed better dielectric properties with a relatively high dielectric coefficient (er = 1580) and a low dielectric loss (tanδ = 2.94 %). Besides these, a high remnant polarization (Pr = 8.26 μC/cm2) and a low coercive field (Ec = 0.33 kV/mm) were also obtained on this composition. Moreover, the influence of sintering temperature on the microstructure development and electrical properties of BCZT–1.2 mol% Mn ceramics has also been studied.

Synthesis of Hollow Ba<sub>0.7</sub>Sr<sub>0.3</sub>TiO<sub>3 </sub>Nanocubes by Using Molten Hydrated Salt as a Solvent

Perovskite Ba0.7Sr0.3TiO3 nanocubes with a hollow structure were prepared by molten hydrated salt method at 180 °C for 15 h, using Ba (OH)2·8H2O, Sr (OH)2·8H2O and anatase-TiO2 as raw materials without any additive or template. The phase composition, morphology and microstructure of the products were characterized by XRD, SEM, TEM and HRTEM. The XRD result indicates that the products are phase pure cubic Ba0.7Sr0.3TiO3, with the calculated unit cell a=0.3965 nm. The SEM, TEM and HRTEM results show that the products with polycrystalline structure are composed of the hollow nanocubes whose average edge length is about 180 nm, and their morphologies are greatly influenced by reaction temperature and reaction time. In addition, the formation mechanism of the hollow nanocubes also was discussed.

Relationship between powder structure and electrochemical performance of Ba0.5Sr0.5Co0.8Fe0.2O3 − δ cathode material

Highly pure Ba0.5Sr0.5Co0.8Fe0.2O3 − δ (BSCF) perovskite nanocompound was synthesized via glycine-nitrate process (GNP) and coprecipitation-azeotropic distillation method (ADM), respectively. Compared to ADM, GNP was proved to facilitate the synthesis of BSCF powder with small crystal and particle sizes as well as large surface area. BSCF material was employed as the cathode of solid oxide fuel cell (SOFC) incorporating with Sm0.2Ce0.8O1.9 (SDC) electrolyte. Linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) tests indicated that the GNP powder-based cathode not only exhibited high electrocatalytic activity but also possessed low oxygen diffusion resistance due to the high porosity. As a result, the cell with GNP powder-based cathode showed a power density of 0.35 W cm−2 when the voltage was 0.7 V at 650 °C. Furthermore, the cathode performance was significantly improved at the high current density condition.

Phase pure (Ba0.3Sr0.7)(Zn1/3Nb2/3)O3 nanocrystalline particles synthesized by sol–gel technique at low temperature and their application

Phase pure (Ba0.3Sr0.7)(Zn1/3Nb2/3)O3 (BSZN) perovskite ceramic nanocrystalline particles were synthesized at low temperature with high reaction yield and high synthetic reproducibility using the sol–gel technique. The results showed that high-purity perovskite BSZN phase with high crystalline quality was obtained at 800 °C, that is, the volatilization of ZnO was successfully overcome. The nanocrystalline particles were about 20–30 nm in diameter with regular and uniform spherical shapes, high dispersive properties, and less aggregation. The pellets made by these nanoparticles had excellent dielectric properties: dielectric constant \( \varepsilon_{\text{r}} \) 40.5, temperature coefficient of resonant frequency \( \tau_{\text{f}} \) 0.5 × 10−6/ °C, and quality factor Q × f: 75,000 at 3.89 GHz, and a high relative density of 98.1 %.

Influence of Al2O3 additive on the dielectric behavior and energy density of Ba0.5Sr0.5TiO3 ceramics

High dense Ba0.5Sr0.5TiO3 ceramics with Al2O3 additives have been prepared by a method combined the sol–gel process and the solid state reaction. Phase compositions, microstructure and dielectric behaviors are investigated systematically. Our experiment results reveal that the Al2O3 additives reduce the dielectric constant slightly and increase the breakdown strength greatly due to the refined microstructure and the formation of the second phases. The estimated energy density of Ba0.5Sr0.5TiO3 ceramics with optimized Al2O3 additives is improved by 1.5 times as compared with that of pure Ba0.5Sr0.5TiO3 ceramics.