Effects of ZnNb2O6 addition on BaTiO3 ceramics for energy storage

BaTiO₃ ceramics were prepared using solid state reaction with addition of ZnNb₂O₆, to investigate the effects of ZnNb₂O₆ addition on structure and properties. The results show that the ZnNb₂O₆ addition lowers sintering temperature, decreases grain size, while introduces second phase (Ba₂Ti₅O₁₂) for x ≥ 7.26 wt%. The dielectric breakdown strength is enhanced with the increasing doping level of ZnNb₂O₆ and reaches a maximum value at x = 7.26 wt%, exhibiting a maximum energy storage capability.     

Effects of Bi2O3 and Cr2Ti3O9 Co-doping on dielectric properties in BaTiO3-based ceramics

A microwave ceramic with general composition (1-x-y) BaTiO₃ + x Cr₂Ti₃O₉ + y Bi₂O₃ has been prepared by solid state synthesis at 1300-1400 °C. The phase composition, perovskite structural parameters and dielectric properties have been obtained by X-ray diffraction and dielectric measurements as a function of chemical composition and temperature. At low doping levels the formation of BaTiO₃-based solid solution has been found. The precipitation of BaCrO₃ has been detected at x = y = 2.0 mol%. A model of the incorporation of Cr³⁺ and Bi³⁺ ions into BaTiO₃-based crystal lattice has been proposed. Diffused phase transition in the temperature range 100-140 °C have been revealed by dielectric measurements for different ceramic composition. As high dielectric constant as 7311 and as low dielectric loss as 0.02 have been found for the composition of 0.98BaTiO₃-0.01Cr₂Ti₃O₉-0.01Bi₂O₃.     

Low temperature solid-phase synthesis of tetragonal BaTiO3 powders and its characterization

We report an alternative synthesis route for tetragonal and submicron barium titanate particles through a low temperature isothermal heat treatment of a precursor powder obtained from the BaO₂-TiO₂-C mixture utilizing combustion synthesis technique. Effort has been concentrated on the investigation and optimization of the synthesis process including combustion temperature and velocity, heat treatment procedure, and the characteristics of the powder obtained. It was shown that precursor powder prepared by the combustion method easily transformed to the tetragonal BaTiO₃ starting from 700 °C. Characterization of the products was performed by powder X-ray diffraction, scanning electron microscopy (SEM) and BET. From the results, it has been found that the formation of tetragonal BaTiO₃ powder at low temperature is conditioned by high chemical activity and specific characteristics of combustion products. The BaTiO₃ specimens were found to possess high dielectric constant and low dissipation factor at room temperature.     

Growth and dielectric properties of BaTiO3 thin films prepared by the microwave-hydrothermal method

Polycrystalline BaTiO₃ thin films were grown on Ti-covered polymer substrates at 80 °C using the microwave-hydrothermal technique. Onset of BaTiO₃ formation occurred almost instantaneously at 80 °C and complete film coverage was achieved within 2 min. Longer reaction time was necessary for extensive grain growth to achieve dense films. Good quality capacitor films were only achieved at 4 h reaction time but loss tangents were high. Film dielectric constant and dielectric loss values of as-grown M-H films decreased with longer reaction time. Oxygen plasma treatment improved loss tangents to 4% by removal of both absorbed moisture and lattice hydroxyls.     

Preparation and electrical properties of nanoporous BaTiO3

Nanoporous barium titanate with high specific surface area was prepared from co-gel precursors through solvothermal method followed by supercritical drying. The samples were accumulated by BaTiO₃ nanoparticles with excellent crystallinity. The BaTiO₃ obtained at 60 °C exhibited a high BET surface area of 117 m²/g. The porosity reduced with the increasing solvothermal temperature. Raman spectra indicated that the solvothermal-synthesized BaTiO₃ was composed by both cubic phase and tetragonal phase. The relations between dielectric properties and the porosity of the samples were also investigated. The introduction of pores reduced the dielectric constant obviously. The dielectric constant of the obtained sample increased with the decrease of the porosity.     

Microstructure and ferroelectric properties of epitaxial BaTiO3/SrRuO3/SrTiO3 (001) films grown by pulsed laser deposition under high oxygen pressure

BaTiO₃ films were epitaxially grown on SrTiO₃ (001) substrates buffered with SrRuO₃ films as bottom electrode by pulsed laser deposition under high oxygen pressure of 30 Pa. The quality of the BaTiO₃/SrRuO₃/SrTiO₃ multilayer films was analyzed by means of X-ray diffraction, atomic force microscopy and transmission electron microscopy. BaTiO₃ films were found to be highly c-axis-oriented tetragonal phase with c/a = 1.002. The dielectric constant first increased with increasing temperature, and showed a peak at the Curie temperature of about 356 K. The films had well-saturated hysteresis loops with a remnant polarization of 7.3 μC/cm² and a coercive field of 29.5 kV/cm at room temperature.     

Effects of Ho2O3 addition on defects of BaTiO3

Effects of Ho₂O₃ addition on defects of BaTiO₃ ceramic have been studied in terms of electrical conductivity at 1200 °C as a function of oxygen partial pressure (P_O2°) and oxygen vacancy concentration. The substitution of Ho³⁺ for the Ti site in Ba(Ti_1−xHo_x)O_3−0.5x resulted in a significant shift of conductivity minimum toward lower oxygen pressures and showed an acceptor-doped behavior. The solubility limit of Ho on Ti sites was confirmed less than 3.0 mol% by measuring the electrical conductivity and the lattice constant. Oxygen vacancy concentrations were calculated from the positions of P_O2° in the conductivity minima and were in good agreement with theoretically estimated values within the solubility limit. The Curie point moved to lower temperatures with increasing the oxygen vacancy concentration and Ho contents.     

Microstructure and dielectric characteristics of Ni ion doped BaTiO3 nanoparticles

In this article, we report the effect of nickel oxide (NiO) addition on the microstructure and the dielectric properties of nano-barium titanate (BaTiO₃). Nickel ion doped barium titanate nanoparticles have been synthesized through a chemical route using polyvinyl alcohol (PVA). The concentration of Ni²⁺ varies from 0 to 1.6 mol% in the specimens. The particle diameters in the specimen lie in the range of 24 nm to 35 nm. It is seen that the dielectric permittivity in doped specimens is enhanced compared to that of undoped BT ceramics. The dielectric permittivity shows maxima in the specimen containing 0.6 mol% of dopant concentration. The results are explained in terms of the change in lattice parameter c and a of the specimens.     

Growth and dielectric properties of solvothermal BaTiO3 polycrystalline thin films

Polycrystalline BaTiO₃ thin films were grown solvothermally on Ti-covered substrates in ethanol, distilled water and 1,4-butanediol at 80 °C, 150 °C and 200 °C. Films grown in organic media are finer grained and required more stringent crystallization conditions due to lower solubility of constituent ions. Solvothermal films exhibit less severe proton incorporation. Solvothermal films grown close to the boundary crystallization conditions tend to have higher frequency dispersion and loss tangents. Dielectric properties of BaTiO₃ films grown in ethanol are comparable to that of hydrothermal films. Butanediol-derived films have lower dielectric constants than the aqueous equivalent.     

Semiconducting BaTiO3-CuO mixed oxide thin films for CO2 detection

A full study of the BaTiO₃-CuO thin-film technology properties as carbon dioxide sensing material is presented. The coatings are deposited by RF-Sputtering and the CO₂ concentration is monitored by impedance measurements. Theoretical foundations are correlated to the experimental results and the principal fabrication and operation parameters are clarified: working temperature and frequency, thickness influence and the introduction of silver as an additive. The BaTiO₃-CuO layer shows higher sensitivity than the actual low-cost commercial CO₂ sensors in the range of the principal applications.     

Microstructure and magnetic properties of BaTiO3-(Ni,Zn)Fe2O4 multiferroics

The microstructures of composite xBaTiO₃-(1−x)(Ni_0.5Zn_0.5)Fe₂O₄ (BT-NZF) multiferroics with various mixing ratios (x = 0.50, 0.60 and 0.70) are investigated by means of electron backscatter diffraction (EBSD) and magnetic force microscopy (MFM). The EBSD measurements reveal a change in the texture of the ferrite and the BaTiO₃ grains upon increasing the ferrite content in the sample. The sample with x = 0.70 exhibits the best ferrite texture, where only some directions are present. Furthermore, the resulting grain sizes vary from several µm (x = 0.50) to about 100 nm in the sample with x = 0.70. The MFM images reveal the presence of magnetic domains being extended over several adjacent grains, which according to the EBSD data may comprise different crystallographic orientations. In this way, we can explain the differences in the magnetic contrast obtained.     

Hydrothermal synthesis of single-crystal BaTiO3 dendrites

In this paper, we report a simple hydrothermal method without any surfactants, for the first time, to synthesize single-crystal BaTiO₃ dendrites. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron diffraction (ED), and high-resolution transmission electron microscopy (HRTEM). The KOH concentration was found to be vital to the final formation of BaTiO₃ dendrites. An obvious morphology evolution from sphere-like shape to dendrite was observed when KOH concentration was decreased from 1 M to 0.1 M. It is rational to expect that dendritic structures of other perovskite oxides may also be synthesized by this simple method.     

Structural and gas sensing behavior of nanocrystalline BaTiO3 based liquid petroleum gas sensors

In this paper nanosized BaTiO₃ thick films based gas sensor has been fabricated for liquid petroleum gas (LPG). Doping with different concentrations of metal oxides influenced the sensitivity of BaTiO₃ thick films for LPG sensor. We present the characterization of both their structural properties by means of X-ray powder diffraction (XRD) and the electrical characteristics by using gas-sensing properties. X-ray powder diffraction analyses revealed the persistence of cubic phase with grain growth 65 nm. The LPG-sensing properties of BaTiO₃ thick films doped with CuO and CdO are investigated. It was found that 10 wt.% CuO: 10 wt.% CdO doped BaTiO₃ based LPG sensor shows better sensitivity and selectivity at an operating temperature 250 °C which is an important commercial range for LPG alarm development. Incorporation of 0.3 wt.% Pd doped CuO:CdO:BaTiO₃ element shows maximum sensitivity with high cross selectivity to the other gases including CO, H₂ and H₂S at an operating temperature 225 °C for low concentrations of LPG sensor.     

Influence of strontium substitution on the dielectric properties of Ca(1 − x)SrxTi0.9Zr0.1O3 solid solutions

A conventional solid-state reaction has been used to synthesize the perovskite Ca_(1 − x)Sr_xTi_(1 − y)Zr_yO₃ (y = 0.1). The aim of this study is focused on the development of new materials with complex perovskite structure and on their dielectric property improvement. The temperature and substitutional ratio effects on the different phase evolutions is investigated by X-ray diffraction (XRD) and scanning electron microscope observations. These ceramics sintered at 1500 °C, present a density higher than 95% and their dielectric properties are significantly affected by the substitution. The CaTiO₃ ceramic present a relative permittivity of 190 and the temperature coefficient of the permittivity of − 1828 ppm/C°. The substitution with zirconium (for x = 0 and y = 0.1: Σ = 145; |Σ = − 917 ppm/C°). Both permittivity and temperature coefficient values decrease; however, an opposite effect is observed when substituting with the strontium. With increasing an x value and maintaining a y value constant (y = 0.1), the dielectric constant increases and the temperature coefficient remains constant. Therefore, the dielectric properties of CaTiO₃ ceramics are improved with the combined substitution.     

Study on the microstructure and dielectric properties of X9R ceramics based on BaTiO3

This paper investigated the microstructure and dielectric properties of BaTiO₃-Pb(Sn, Ti)O₃ system ceramics. The Curie point of BaTiO₃ is 130 °C. When the temperature is higher than 130 °C, the dielectric constant of BaTiO₃ drops severely according to Curie-Weiss law. Pb(Ti, Sn)O₃(PTS) was selected to compensate the dielectric constant doping of BaTiO₃ since it has high Curie temperature (Tc) point that is about 296 °C. The Curie temperature (Tc) point of BaTiO₃ was broadened and shifted to higher temperature because of the doping of PTS, so the temperature coefficient of capacitance (TCC) curves of the ceramics based on BaTiO₃ was flattened. When 2 wt% Pb(Ti_0.55Sn_0.45)O₃ was added, the sample showed super dielectric properties that the dielectric constant was >1750 at 25 °C, dielectric loss was lower than 2.0% and TCC was <±10% from −55 °C to 200 °C. Therefore the materials satisfied EIA X9R specifications.     

Enhanced ferroelectric properties of Fe-doped BaTiO3 thin film deposited on LaNiO3/Si substrate by sol–gel technique

The ferroelectric thin films of Fe-doped BaTiO₃ and undoped BaTiO₃ were prepared on LaNiO₃ coating Si substrates by sol–gel technique. It was found that a small amount of Fe dopant could significantly enhance the ferroelectric properties of the BaTiO₃ thin film. The remnant polarization of Fe-doped BaTiO₃ thin film at room temperature reached to 14.9 μC/cm². The loss tangent, compared to the undoped BaTiO₃ film, was increased with frequency increasing and the dielectric constant was decreased. The possible mechanism of enhanced ferroelectric properties of Fe-doped BaTiO₃ thin film was discussed. The results show the potential role of Fe dopant in improving the ferroelectric properties of BaTiO₃ thin film.     

Variations of microstructures and electrical properties of Bi4Ti3O12/SrTiO3/(La0.5, Sr0.5)CoO3/MgO epitaxial thin films by annealing

Epitaxial thin films of a heterostructure with Bi₄Ti₃O₁₂(BIT)/SrTiO₃(ST) were successfully grown with a bottom electrode consisting of La_0.5Sr_0.5CoO₃(LSCO) on MgO(001) substrates using pulsed laser deposition. The grown BIT and ST (001) planes were parallel to the growth surface with the orientation relationship of BIT <110>//ST <010>. In the as-deposited film, the BIT (001) plane appeared to expand to relieve a lattice mismatch with the ST (001) plane. However, annealing for 20-40 min induced the BIT (001) plane to contract horizontally with its c-axis expanding, which was associated with a local perturbation in the layer stacking of the BIT structure. This structural distortion was reduced in the film annealed for 1 h, with restoration of the periodicity of the layer stacking. Correspondingly, the dielectric constant of the as-deposited film was increased from 292 to 411 by annealing for 1 h. In parallel, the film was paraelectric but became more ferroelectric, with the remanent polarization and the coercive field changing from 0.1 μC/cm² and 14 kV/cm to 1.7 μC/cm² and 69 kV/cm, respectively.     

Charge recombination reduction in dye-sensitized solar cells by depositing ultrapure TiO2 nanoparticles on “inert” BaTiO3 films

Ultrapure TiO₂ nanoparticles (∼5 nm in size) were supported on “inert” BaTiO₃ films by TiCl₄ treatment, which was used to fabricate dye-sensitized solar cells (DSSCs). The optimized electrode, designated as BaTiO₃/TiO₂(4), was obtained upon four cycles of TiCl₄ treatment. DSSC with BaTiO₃/TiO₂(4) electrode exhibits superior power conversion efficiency (PCE) compared to that with conventional anatase TiO₂ (∼25 nm in size) electrode. The interfacial charge recombination kinetics was investigated by electrochemical impedance spectroscopy (EIS) and intensity-modulated photocurrent/photovoltage spectroscopy (IMPS/IMVS). In contrast to DSSC with anatase TiO₂ electrode, the dramatically enhanced electron lifetime for DSSC with BaTiO₃/TiO₂(4) electrode could be attributed to the decrease of recombination reaction at the TiO₂ photoelectrode/electrolyte interface. It is proposed that the lower interfacial charge recombination can be related to the relatively shallower trap distributions in DSSC with BaTiO₃/TiO₂(4) electrode.