Papers by Keyword: Barium Titanate

Abstract: Barium titanate/graphene oxide/polyurethane (BTO@GO@PU) composite membranes for microwave absorption were designed and fabricated by mechanical-blending of BTO and GO in PU medium, followed by mold formation. The cross section morphology of the BTO@GO@PU membrane indicated that the BTO nanoparticles with 450 nm average diameter are successfully incorporated into the PU matrix. Mechanical tensile measurement showed that, as the amount of BTO nanoparticles increased from 5 wt% to 20 wt%, the elastic modulus of the corresponding membrane increased up to 23.0 MPa elongation with the elongation above 450 %. Microwave absorption property of the BTO@GO@PU membranes were evaluated by measuring its reflection loss in the frequency range of 0.1-18 GHz. With the addition of BTO up to 20 wt%, the maximum absorptivity of the composite reached up to 51 %. This is attributed to the dielectric loss of BTO nanoparticles.

Abstract: The thermal decomposition was used to prepare BaTiO₃ powders. Using BaCO₃ and TiO₂ powders as precursors and heat treatment in the temperature range of 600-1000 °C for 6 hr. The final product (BaTiO₃) proceeds through a trace amount of Ba₂TiO₄. The phase transformation was investigated by X-ray diffraction (XRD) as a function of sintering temperature. The results show that the microstructures of BaTiO₃ were developed during sintering at different temperature. In additional, the particle growth of BaCO₃ and TiO₂ are the major factors to affect of the particle growth mechanism.

Abstract: Conductor–insulator composites have been extensive researched for high dielectric constant. Most of them concentrated on metal polymers or metal ceramics. Barium titanate–carbon fibers composites were prepared by using a solid state reaction process with carbon fibers contents ranging from7 vol% to 23 vol%. Due to the high-aspect-ratio of carbon fiber, it was easy to produce a conducting network at much lower volume fraction. FESEM images illustrated that the carbon fibers influenced the densification and microstructure of the ceramics. Besides, addition of carbon fibers led to increase in dielectric permittivity, also had effects on the dielectric loss and ac conductivity. The dielectric and conductivity properties as a function of carbon fibers volume fraction were explained by the percolation theory.

Abstract: Barium titanate (BaTiO₃) with its perovskite structure is a promising dielectric material for many applications such as transducers, actuators, high-k dielectrics and multilayer ceramic capacitors (MLCC). In this study, we have investigated the effect of sintering time on dielectric properties of BaTiO₃ and Nb-doped BaTiO₃. BaTiO₃ was doped with 0.3 mol % niobium oxide (Nb₂O₅). At first, nanosized pure BaTiO₃ and Nb₂O₅ doped BaTiO₃ were milled, dried and pressed into pellets to prepare green samples. Then, the samples were sintered at 1275°C for different time periods ranging from 2 to 5 hrs. Single stage sintering was adopted for the densification of prepared samples. Microstructure of the sintered samples was investigated employing Field-emission scanning electron microscope (FESEM). Dielectric properties of the samples were measured using an impedance analyzer. Finally, a correlation was established between the dielectric properties of the sintered samples and their microstructure. Nb has shown to provide strong inhibiting effect after sintering the samples in the range of 2 to 5 hours at 1275°C thereby, resulted in higher dielectric properties of doped BaTiO₃ ceramics compared to that of pure BaTiO₃. The best room temperature dielectric constant of 7200 was obtained for Nb doped BaTiO₃ sintered at 1275°C for five hours. Such improved dielectric constant is attributed to the optimum grain size of about 1 micron at this sintering temperature.

Abstract: The structure-property relationship of 0.3, 0.5 and 0.7mole% lanthanum (La₂O₃) doped Barium titanate (BaTiO₃) ceramics prepared by solid state sintering under different sintering conditions were investigated in this research. The raw materials were La₂O₃ (grain size=~80nm) and BaTiO₃ (grain size=100nm) powders. Field Emission Scanning Electron Microscope (FE-SEM) was used to examine grain size and surface morphology of sintered pellets & X-Ray Diffraction analysis was conducted to identify crystal structure. The results showed significantly improved grain size and electrical properties of BaTiO₃ for 0.5 mole% La₂O₃ with desired grain size (0.8-1.3μm), high densification (>90% theoretical density) and stable dielectric constant (12700) at room temperature (f=100Hz) by lowering curie temperature around 30^oC by sintering at 1300^oC for 8 hrs. A gradual deterioration follows with increased doping concentration. So the research revealed that proper La³⁺ concentration can inhibit grain size and lower Curie temperature hence significantly improving the electrical properties of BaTiO₃ ceramics.

Abstract: Undoped barium titanate and lanthanum (La) doped barium titanate (BaTiO₃) were studied for ferroelectric properties with the formula of Ba_1-xLa_xTi_1-x/4O₃ for x=0.1 and being prepared by using conventional solid state method reaction. The pure phase of this composition which x=0 were found at final heating temperatures starting from 1300°C and x=0.1 at 1350°C for overnight in air with intermittent grinding. The changes in the crystal structure of the composition were detected by using X-ray diffraction. Impedance Spectroscopy analysis is carried out to determine the dielectric properties for undoped BaTiO₃ and La doped BaTiO₃ for x=0.1.

Abstract: Barium titanate (BT) additive in lanthanum modified lead zirconate titanate (PLZT) was used to modify the microstructure and resultant properties of (1-x) PLZT– x BT where x= 0, 0.05, 0.10, 0.15, 0.20 and 0.25. Oxide powders were synthesized by mixed oxide synthetic route via a rapid vibro-milling technique. All of samples were sintered at 1275°C with the soaking time of 4 h. The ceramic samples were investigated for phase formation and evolution, dielectric behavior and ferroelectric properties. Introduction of BT in PLZT lattice resulted in ferroelectric tetragonal-rhombohedral structure, and further increase of BT content resulted in stabilizing the ferroelectric tetragonal perovskite phase. Dielectric behavior and ferroelectric properties were examined as a function of BT content.

Abstract: Rising worldwide demands for energy encourages development of high-efficiency energy storage and capacitor components. Main requirements for dielectric materials employed in fabrication of high energy density capacitors include high dielectric constant, high dielectric breakdown strength, and low dielectric loss. Owing to its high dielectric constant and low dielectric loss [1], barium titanate is among common capacitor materials. Tailoring of dielectric properties of barium titanate can be achieved through controlled chemical composition, microstructure, and crystal structure. Synthesis and processing techniques, as well as doping of barium titanate, can be key factors to control the composition and structure, which consequently contribute to enhancement of dielectric constant in the material.

Abstract: In this research, Barium titanate (BT) additive in lanthanum modified lead zirconate titanate (PLZT) was used to stabilize the PLZT ceramics. Oxide powders were synthesized by mixed oxide synthetic route via a rapid vibro-milling technique. It was prepared with the chemical formula of 0.95 Pb_0.91La_0.09 (Zr_0.65Ti_0.35)_0.9775O₃ -0.05 BaTiO₃ to investigate the dielectric properties of PLZT ceramics_. The modified PLZT ceramics were fabricated at variation of sintering temperatures of 1200-1275°C for 4 hours. By employing X-ray diffraction (XRD), it was found a pure perovskite with rhombohedral structure. The relaxor behavior was observed from the dielectric measurements. The suitable sintering temperature of 0.95 PLZT - 0.05 BT was 1275°C (ε_r=10463, tanδ=0.0125 and T_m=70°C).

Abstract: La-doped barium titanate (BaTiO₃) was prepared using conventional solid state synthesis route. All peaks for sample x=0 are approaching the phase pure of BaTiO₃ structure with tetragonal crystal structure (P4mm). Sintering of pressed powder are performed at 1300oC, 1400oC and 1450oC for overnight for pure BaTiO₃ and 1350oC for 3 days for BaTiO₃ doped lanthanum with intermittent grinding. Phase transition was studied by different x composition. The changes in the crystal structure of the composition x=0.1 and 0.2 were detected by using X-ray diffraction (XRD). The phase changes between tetragonal-cubic and cubic-tetragonal depending on the temperature. Rietveld Refinement analysis is carried out to determine the lattice parameter and unit cell for BaTiO₃.