Papers by Keyword: BaTiO₃

Abstract: The barium titanium based PTC ceramic with two kind of colors, light blue and yellow, were obtained by changing sintering processing. In order to reveal the relationship between color and electrical properties of the ceramics. The phase structure and microstructure of as synthesized samples were investigated by powder X-ray diffraction (XRD) and scanning electron microscopic (SEM) analysis. The micro area elements were characterized by electron probe micro-analyzer (EPMA) and x-ray photoelectron spectrometer (XPS). The thermo-sensitive properties were studied by resistance-temperature measurement system. The results reveal that two kinds of PTC ceramics have the same structure, similar elements, but different microstructure and valence concentration of titanium. It is suggested that difference of color of the PTC ceramics are originated from the defect concentration of titanium.

Abstract: BaTiO₃/La₂O₃ nanopowders were synthesized by a low-temperature soft chemical method, and then the BaTiO₃/La₂O₃ composite ceramics were prepared. X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM) were used to characterize the prepared powders and ceramics. And the dielectric properties of the BaTiO₃/La₂O₃ composite ceramics were studied. The results revealed that some of La³⁺ ions dissolved into the lattice of BaTiO₃ at Ba-site and the rest remained at grain boundaries in oxide form of La₂O₃. With the content of La₂O₃ increasing, Curie peak of the BaTiO₃/La₂O₃ composite ceramics moved to a lower temperature, and the dielectric loss of the BaTiO₃/La₂O₃ composite ceramics decreased significantly, while the dielectric tunability still kept a relatively high value. The dielectric permittivity and dielectric loss of BaTiO₃/La₂O₃ composite with 10 at.% La₂O₃ was 227 and 0.0026 at 25 ^oC and 10 kHz, meanwhile the tunability was up to 17.4% under the electric field of 20 kV/cm.

Abstract: Composites between mullite and modified BT were prepared by a conventional technique. The samples were calcined at 1300 °C for 2 h. The composites were sintered at 1250 °C for 2 h. The dielectric and mechanical properties the samples were investigated. The mechanical properties were found to improve after sintering at a suitable temperature. Addition of the BT produced an improvement in dielectric constant due to the BT has high piezoelectric properties. A higher dielectric constant for a sample contained higher amount of the BT was related with a higher polarization in the samples.

Abstract: BaTiO₃ (BT) nano powder was prepared via non-hydrolytic sol-gel (NHSG) method by using barium acetate, titanium tetrabutoxide as precursors, glycerol and ethanol as solvents. The samples were characterized by DTA-TG, XRD, FT-IR and TEM. The influences of heat treatment temperature on the morphology and the microstructure of powder were studied, and the mechanism of low temperature synthesis was discussed. In addition, the de-esterification action between the precursors was also described in detail. The results show that the formation of Ba-O-Ti bond in the xerogel via NHSG route is duo to the de-esterification polycondensation of barium acetate and titanium tetrabutoxide, which plays the key role in the low temperature synthesis of BT powder. With the temperature rising to 700 °C, BT nano powder with good dispersion and even size distribution can be acquired and the average particle diameter is about 25 nm. Overlow and overhigh heat treatment temperatures are both not beneficial to the preparation of BT nano powder.

Abstract: Colossal permittivity (CP) in BaTiO₃ (BT)-based polycrystalline ceramics with normal grain sizes has been successfully obtained in yttrium (Y) doped BT ceramics (BYT) via a simple and effective method. Considering the necessary factors for CP formation mechanism, well designed doping condition and sintering procedure were carried out in the sample preparation. Characterizations show that BYT is with a pure tetragonal perovskite structure and the grain growth is depressed under the action of Y donor doping. The frequency independence of permittivity and Debye-like relaxation related to Maxwell-Wagner relaxation which occurred at the interfaces between semiconducting grains and insulating grain boundaries can be detected. These are induced by an internal barrier layer capacitance (IBLC)-type structure which formed under an overall and carefully designed synthesis procedure. But the temperature independence of permittivity does not arise because of the particular tetragonal structure and micron dimension grain sizes of BYT.

Abstract: We investigated the effect of the donor-doped content on the positive temperature coefficient of resistivity (PTCR) of (Ba_1-xSm_x)TiO₃ (BST) Based Ceramics that were sintered at 1300 °C for 30 min in a reducing atmosphere and re-oxidized at 850 °C for 1 h. The results indicated that the resistance jump first increased and then decreased with an increase of the donor-doped concentration. Moreover, the specimens achieved a low room temperature resistivity of 383.1 Ω·cm at a donor-doped content and exhibited a pronounced PTCR characteristics with a resistance jump of 3.1 orders of magnitude. Furthermore, the RT reisistivity of the samples reduced and increased with the increasing of the donor-dopant content in the range of 0.1−0.5 mol% Sm³⁺. In addition, the effect of the Sm³⁺-doped concentration on the grain size of the ceramics was investigated in our paper.

Abstract: We investigated the influence of the Sm-doped contentration on the electrical properties and PTC effect of Ba-excess BaTiO₃ Based Ceramics, which were fired at 1300 °C for 30 min in a reducing atmosphere and then reoxidized at 850 °C for 1 h. The results showed that the donor dopant affected PTC characteristics and the electrical properties of the BSMT ceramics, whose room temperature resistivity first decreased and then increased with an increase in the Sm³⁺-doped content across the range from 0.1 to 0.5 mol%. The BSMT specimens exhibited a remarkable PTC effect, with a resistance jump greater by 2.7 orders of magnitude, along with a low room temperature resistivity of 128.6 Ω∙cm at the donor-doped content of 0.3 mol%. The influence of the donor dopant on the grain size of the as-fired samples has been also investigated.

Abstract: Size controllable Barium titanate nanoparticles were synthesized in microemulsion consisting of water, OP-10, hexanol and cyclohexane under atmospheric pressure and low temperature, with Ba (OH)₂·8H₂O and tetrabutyl titanate used as starting reactants. Products were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX). The results show that 65°C is the proper temperature for the synthesis. The particle size can be controlled by varying the reactants’ concentration, ω value (molar ratios of water to surfactant) and aging time.

Abstract: In this paper, Ni_0.60Cu_0.24Zn_0.16Fe₂O₄/BaTiO₃ composites of BaTiO₃ (BT)/NiCuZn (NCZ) with mass ratios (x) equal to 5%, 10%, 15% or 20% were synthesised by a conventional solid-state reaction method and sintered at 900oC to adapt to low temperature co-fired ceramic technology. X-ray diffraction results showed that the composites were composed of BT and NCZ phases. The microstructures of the sintered composite materials were observed and analysed using scanning electron microscopy. The dielectric and magnetic properties of the composites were improved effectively with increasing BaTiO₃ content. The influences of different compositions on the electromagnetic properties of the composites were investigated.

Abstract: The effect of milling time and sintering process on the dielectric properties of BaTiO3-based X9R ceramics was investigated. The characterization of the raw powders and the sintered ceramic was carried out by X-ray diffraction and scanning electron microscopy. The particle size distribution of the mixed powders was examined by Laser Particle Size Analyzer. The results shown that with the milling time extended, the Cruie Peak was depressed, or even disappeared. Moreover, with the rise of sintering temperature, the dielectric constant of the ceramics increased and the dielectric loss decreased gradually. Eventually, by milling for 11h and sintering at 1090°Cfor 2h, good dielectric properties were obtained, which were ε25°C≥ 2526, εr/εr25°C≤± 12% (–55~200°C), tanδ≤1.12% (25°C).