Liangying Zhang

Dielectric nonlinear characteristics of Ba(Zr0.35Ti0.65)O3 thin films grown by a sol-gel process

Ba(Zr0.35Ti0.65)O3 (BZT) thin films were deposited via a sol-gel process on Pt-coated silicon substrates. The BZT films were in the perovskite phase and had polycrystalline structure. Temperature-dependent dielectric measurements revealed that the thin films have relaxor behavior and diffuse phase transition characteristics. The tunability K of the dielectric constant (at 600 kV/cm) is about 40% in the temperature range of 179–293 K. The improved temperature stability from this BZT thin film is beneficial to applications requiring a wide range of operating temperatures, thereby eliminating the need for environmental controls. Although the K value is not extraordinarily large compared to (Ba,Sr)TiO3, the low dielectric constant of BZT is attractive for microwave frequency applications. This provides an additional possibility in balancing K and dielectric constant through materials engineering for optimum device performance.

Structural and dielectric properties of Ba(ZrxTi1−x)O3 thin films prepared by the sol–gel process

The Ba(ZrxTi1−x)O3 (BZT) thin films were prepared by deposition of relevant materials on LaNiO3-coated silicon substrates by the sol–gel process. The films thus prepared show a (100) preferred orientation in structure and vary with zirconium content. With the addition of Zr, the grain sizes of films were found to decrease, whereas their microstructure became dense. The changes in the films grain sizes and microstructure were attributed to the addition of Zr to the BaTiO3 lattice. Dielectric constant measurements revealed that the thin films show a relaxor behaviour and have a diffuse phase transition characteristic when x is 0.35. The hysteresis loops of the dielectric properties of films measured at room temperature were considered to be the result of the polarization state of the domains in these films in both the ferroelectric or paraelectric state. This leads to a distribution of Curie temperatures. The highest figure of merit value, K, was found for the BZT thin film with a very low dielectric constant. This indicates that BZT films have the potential to be used as microwave tunable devices with superior performance.

Sol-gel preparation and characterization of transparent KTiOPO4/SiO2 nanocomposite glass for second harmonic generation

Abstract A nanocomposite glass consisting of sol–gel derived nanocrystalline KTiOPO 4 (KTP) and SiO 2 -based glass has been developed. The multicomponent glass in the K 2 O–TiO 2 –P 2 O 5 –SiO 2 system has been prepared by the sol–gel method. After heat treatment at temperatures higher than 650°C, the glass transformed into a dense nanocomposite glass containing KTP nanocrystals. The transparent nanocomposite glasses, 10 mm in diameter and 2–3 mm thick, can be obtained by the heat treatment. The transmittance of the polished nanocomposite glasses 0.6 mm thick can be 70% at 0.532 μm wavelength. The structures of the nanocomposite glass in the 20KTiOPO 4 –80SiO 2 systems were analyzed by XRD and TEM. During heat treatment in the temperature range 650–900°C, the KTP nanocrystals precipitate from the multicomponent parent glass. TEM analysis indicated that nanometer sized or larger crystallites of KTP are dispersed in the SiO 2 -based glass. The KTP nanocrystallite size is in the range 10–50(±8) nm. Using a Nd:YAG laser of 1.064 μm wavelength, second harmonic generation (SHG) was clearly observed in the transparent nanocomposite glasses and translucent glass–ceramics. SHG green light (0.532 μm) is so strong that it is observed by naked eye. In contrast, no second harmonic generation was detected in multicomponent K 2 O–TiO 2 –P 2 O 5 –SiO 2 and other SiO 2 -based glass systems. These results suggest that second harmonic generation in the 20KTiOPO 4 –80SiO 2 nanocomposite glass originate from KTP nanocrystals embedded in SiO 2 -based glass. Also, the nanocomposite glasses are chemically stable and can be easily polished. As a result, these transparent nanocomposite glasses have a potential for non-linear optical application.

Microwave characterization of ferrite particles

Several different mixture equations have previously been used to characterize the microwave properties of the ferrite particle-insulating medium mixtures. For very low particle concentrations, these equations give nearly the same results. But when the particle concentration is higher than a few per cent, these equations generally give different results. Based on microwave measurements and numerical calculations, the validity of five well-known mixture equations has been examined in this paper. The experimental results show that both the Bruggeman and QCA-CP (`quasi-crystalline approximation with coherent potential) equations can accurately describe the microwave properties of the ferrite-medium mixtures, and that the Lichtenecker, Logarithm and Maxwell-Garnett equations are not suitable for characterizing the ferrite-medium mixtures over a wide particle concentration range at microwave frequencies. The microwave intrinsic permeability and permittivity spectra of some BaZn2-xCoxFe16O27, Ba4Zn2-xCoxFe36O60 and Ba2Zn2-xCoxFe12O22 ferrite particles have been presented, which were calculated from the measurement data of the ferrite-wax mixtures using the Bruggeman equation. The microwave properties of these ferrite particles have also been discussed. In the 1-6?GHz range, both the real and imaginary parts of permeability of BaZn2-xCoxFe16O27 and Ba4Zn2-xCoxFe36O60 ferrite particles evidently increase with the increasing Co concentration. Both the real and imaginary parts of permittivity of Ba2Zn2-xCoxFe12O22 ferrite particles apparently decrease as the Co concentration increases.

Effects of composition and temperature on gel-formed TiO2/ SiO2 films

Abstract Structure and crystal grain size distribution along the thickness of TiO 2 /SiO 2 thin films prepared by the sol–gel process under various heating temperatures were studied. The X-ray diffraction spectra indicated that the crystalline forms of TiO 2 in the film depend on the TiO 2 content. The phase transformation kinetics depend on the anatase particle size. X-ray grazing incidence analyses indicated that the crystal size decreases along the thickness of the thin film. Increasing the heat-treatment temperature increased the difference in crystal size along the depth of thin film.

Second harmonic generation in transparent KTiOPO4/SiO2 nanocomposite glasses prepared by the sol–gel method

Abstract Transparent bulk xKTP–(1−x)SiO2 nanocomposites, containing nanocrystalline KTiOPO4 (KTP) dispersed in silica glass matrix, were fabricated by the sol–gel method. The transmission properties of KTP/SiO2 have been measured between 2500 and 300 nm and show transmission of 30% at 0.532 μm and 60% at 1.064 μm. The nanocomposite glasses exhibit an UV cut-off at 350 nm. The second harmonic generation (SHG) was observed from xKTP–(1−x)SiO2 nanocomposites or glass-ceramics. The intensity of the SHG signal in the nanocomposites increases as a function of KTP concentration.

The Synthesis, Characterization and Microwave Properties of ZnCo-Substituted W-Type Barium Hexaferrite, from a Sol-Gel Precursor

The preparation of BaZn2 − xCoxFe16O27 W-type hexaferrites powders by a citrate sol-gel method has been investigated. The samples were characterized by TG-DSC, X-ray diffraction (XRD), scanning electron microscopy (SEM). The complex dielectric constant and complex permeability of hexaferrite-paraffin wax composites were measured by the transmission/reflection coaxial line method in the range from 50 MHz to 3 GHz. The dependence of complex dielectric constant and permeability on annealing temperature, composition and measuring frequency was presented.

Determination of microwave complex permittivity of particulate materials

A practical method for determining the broadband microwave complex permittivity of particulate materials is described. In this method, particulate materials are dispersed randomly in paraffin wax; thin disc samples are prepared for measurement from the particle-wax mixtures. During measurements, the samples are backed by a conducting plane, and an open-ended coaxial probe is used to determine the permittivity of the samples. A mixture equation is used to calculate the permittivity of the particulate materials from the permittivity of the samples. The validity of six well known mixture equations is examined. The experimental results indicate that only the QCA-CP and Bruggeman mixture equations can accurately describe the microwave permittivity of the particle-wax mixtures over the wide particle concentration range. To validate this described method, the complex permittivities of PbTiO3 and Pb(Zr0.53Ti0.47)O3 particles are determined over a frequency range of 0.2 to 6 GHz. The determined results are found to be in agreement with the coaxial transmission/reflection measurement results. The advantages and limitations of this method are also discussed in this paper.

Manganese activates caspase-9-dependent apoptosis in human bronchial epithelial cells

Acute inhalation exposure to high levels of manganese (Mn) is associated with pulmonary edema and impaired function. The immune-mediated lung epithelium injury of Mn in vivo and in vitro experiments has been well characterized, whereas its apoptotic effect is not well defined. Our results show that human bronchial epithelial (16HBE) cells undergo caspase-9-mediated cell death in response to Mn. Loss of mitochondrial membrane potential (ΔΨm), the formation of reactive oxygen species and release of cytochrome c were regulated during this process. In addition, decreasing c-Myc level and increasing of phosphorylated p53 (Ser 15) and WAF1/p21 were also taken part in Mn-mediated lung toxicity. Proteasome inhibitor MG132 could increase c-Myc protein in abundance. Taking together, our results demonstrate that caspase-9-dependent intrinsic pathway, the downregulation of c-Myc and the upregulation of p53 and phosphorylated p53 might be responsible for Mn-mediated apoptosis in 16HBE cells. Moreover, c-Myc decrease might be due to increased degradation through the ubiquitin–proteasome pathway.

Studies of Resistivity and Dielectric Properties of Manganese-Doped Barium Titanate Sintered in Pure Nitrogen

This paper investigated the resistivity and dielectric properties of manganese doped barium titanate sintered in pure nitrogen. The influence of variable doping concentration and Ba/Ti ratio on densification, microstructure, resistivity and dielectric properties was studied. A dielectric with permittivity of 1500 and low dissipation factor of 0.01 measured at 1 kHz, meeting the EIA X7R specification of the Electronic Industries Association standards was obtained in this study. Resistivity of materials sintered in pure nitrogen was 10 11 ∼ 10 12 Ω cm. Ceramics sintered in pure nitrogen had higher resistivity than ceramics sintered in air, and the resistivity increased with Ba/Ti ratio increasing.