Zhang Liangying

The dielectric properties and optical propagation loss of c-axis oriented ZnO thin films deposited by sol–gel process

Abstract The c -axis oriented ZnO thin films were prepared on various substrates by sol–gel processes. The stability of solution was examined through solvent and stabilizer. The c -axis orientation and grain size of films were increased with increasing of heat treatment temperature. The optical propogation losses of ZnO films deposited SiO 2 /Si(111) substrates were measured using end-coupling method. The losses result in the scattering of the interface of ZnO/SiO 2 , and the ZnO grain. Dielectric constant and resistivity of thin films deposited on Pt/SiO 2 /Si(111) substrates are, respectively, in the range of 7–13 and 1.7×10 4 ∼9.8×10 5 Ω cm.

Preparation and microwave properties of Co- and Ti-doped barium ferrite by citrate sol-gel process

The citrate sol–gel synthesis method has been used to prepare Ba(CoTi)x Fe12−2x O19 (x varies from 0.2 to 1.0 in steps of 0.2) hexaferrites. Several methods such as X-ray diffractometry, scanning electron microscopy (SEM) and network analyzer (HP8753E) have been used to obtain detailed information on the crystallography and microwave properties of the precursor powders calcined at different temperature. The correlations of Co 2+ Ti 4+ substitution, annealing temperature and frequency with complex permeability, permittivity, microwave absorption of Ba(CoTi)x Fe12−2x O19 ferrites have been studied. All the ferrites annealed at 1100 and 1200 ◦ C exhibit significant dispersion in complex permeability. The dispersion in complex dielectric constant is significant for the samples sintered at 1200 and 1100 ◦ C. The variations of reflection loss have been studied as a function of frequency, Co 2+ Ti 4+ content, and thickness of the absorber.

The optical waveguiding properties of TiO2–SiO2 composite films prepared by the sol–gel process

Abstract We have studied the optical waveguide properties of sol–gel coated TiO 2 –SiO 2 composite thin films. With increasing TiO 2 content the loss of thin films was increased. The loss of thin films was increased and then decreased with increasing annealing temperature. FT–IR spectra, XRD, AFM, and SEM analyses showed that this loss resulted from the scattering of segregations and non-uniform distribution in the films. ©

Preparation and dielectric properties by sol–gel derived PMN-PT powder and ceramic

Abstract A relaxor ferroelectric material, 0.85Pb(Mg 1/3 Nb 2/3 )O 3 -0.15PbTiO 3 with a pyrochlore-free phase, was prepared by using sol–gel method. The metal alkoxide Nb(OC 2 H 5 ) 5 and Mg(OC 2 H 5 ) 2 are substituted by Nb(OH) 5 and Mg(NO 3 ) 2 . During the processing the gel first converted to pyrochlore phase at a calcination temperature of 500°C followed by the formation of pure perovskite phase at 1100°C. The grain size and the dielectric constant increased with an increase in the sintering temperature. The chemical composition analysis shows starting material shift to a higher PT-content (PT∼17%) for the final material.

Characteristics of laser-densified and conventionally heat treated sol–gel derived silica–titania films

Abstract Thin films of various compositions in the system SiO2–TiO2 were prepared by the sol–gel method, with the effects of laser-densification and heat treatment being studied. The etch rate of the resultant coating films was found to change by a factor of almost 1000 for various heat treatment conditions in the temperature range 600∼800°C. By combining laser sintering of selected areas and chemical etching techniques, the large difference between the etch rates of densified and undensified coatings can be used to produce channel waveguide structures. The etched coatings were characterized by X-ray diffraction, Fourier transform infrared spectra and micro-Raman spectra with these studies indicating that crystallization occurs in the region of laser scanning with dimensions corresponding approximately to the width of the beam used.

Dielectric properties under dc-bias field of Ba0.6Sr0.4TiO3 with various grain sizes

Abstract We study the effect of grain size on the dc field dependence of dielectric characteristics in Ba0.6Sr0.4TiO3 ceramics prepared by a sol–gel method. The samples were observed and analysed by SEM and X-ray diffraction. The dielectric constant samples decreases as the applied dc field increases. The influence of the dc field on the loss factor is much less than that on the dielectric constant. With increasing of the applied voltage, the Tc was increased and the peaks were suppressed and broadened. As the grain size increases, The maximum dielectric constant and the percentage change of dielectric constant under a dc field increase. A transition broadening and shift of Tc are observed as grain size decreases.

Direct-current field dependence of dielectric properties in B2O3-SiO2 glass doped Ba0.6Sr0.4TiO3 ceramics

The Ba0.6Sr0.4TiO3 ceramics doped B2O3-SiO2 glass prepared by a sol-gel process and the effect of glass content on the DC field dependence of dielectric characteristics in Ba0.6Sr0.4TiO3 ceramics were studied. The samples were observed and analysed by SEM and X-ray diffraction. The dielectric constant of a BST sample with 1 mol% B2O3-SiO2 sintered at 1250°C was as good as that of undoped BST sintered at 1340°C. The dielectric constant samples decreases as the applied DC field increases. The influence of the DC field on the loss factor is much less than that on the dielectric constant. With increasing of the applied voltage, the Tc was increased and the peaks were surpressed and broadened. With increasing of glass content, the peaks were also surpressed and broadened. The maximum dielectric constant and the percentage change of dielectric constant under a DC field increase.

Preparation and microwave characterization of PbTiO3 ceramic and powder

The ceramics of PbTiO3 and its powders have been prepared by a sol-gel process. The constitution of its phase and structure was examined by x-ray diffraction and Fourier transform infrared spectroscopy. Characterization studies were performed to determine the effects of particle size and degree of tetragonality. The dielectric properties of ceramics and powders of PbTiO3, composited with paraffin, were measured from 1 MHz to 18 GHz. All samples exhibited evidence of relaxation phenomena in their dielectric spectra. The relaxation frequencies increased with decreasing particle size.

Characterization and optical propagation loss of sol-gel derived TiO2/SiO2 films

Thin films of TiO2-SiO2 were prepared by a sol-gel process. The refractive indices and extinction coefficients of these films as a function of wavelength were calculated using optical transmission spectra. The relationships of the fabricating technology, refractive indices and extinction coefficients were studied. With increasing TiO2 content and heat treatment temperature, the refractive index of the films increased. The relationships between the surface roughness, coating layer number, optical propagation loss and preparation technology were studied.

The preparation and microwave properties of Ba3ZnZCo2-ZFe24O41 ferrite by citrate sol-gel process

Abstract A series of Ba 3 Zn Z Co 2− Z Fe 24 O 41 ferrite with Z =0.0, 0.4, 0.8, 1.2, 1.6 and 2.0 had been prepared by citrate sol–gel process, the result showed that the pure Z -type hexaferrite could be obtained by this process at 1200°C for 5 h. The complex dielectric constant and complex permeability were measured in 100 MHz–6 GHz by using transmission/reflection coaxial line method. It showed that the real part of the dielectric constant was almost invariable in the whole measuring frequency for all samples, the imaginary part of the dielectric constant and the real part of the permeability all decreased with the measuring frequency. And nature resonance phenomena were observed in the μ ″ spectra for all samples. It also indicated that substitution of zinc ions had a close effect on the nature resonance frequency of Ba 3 Zn Z Co 2− Z Fe 24 O 41 ferrite, the more the zinc ions was, the lower the resonance frequency.