Key Engineering Materials Vols. 280-283

Abstract: SrBi2Nb2O9 (SBN) with different Bi2O3 contents were prepared by solid-state reaction method and then spark plasma sintering. The Influence of Bi2O3 on the properties of SBN was studied. The results showed that the increased Bi2O3 contents can enhance densification and improve the dielectric properties. This might have close relation to the low melting point of Bi2O3 and special sintering way of SPS, which usually results in some change in micro-structure.

Abstract: Ba1-xSrxTiO3 ceramic (BST) was one of the promising materials applied in phased array antennas due to its excellent dielectric properties. Ba1-xSrxTiO3 ceramic was prepared by traditional solid state reactions. Effects of different amount of ZrO2 as additive upon the dielectric properties of BST were investigated. The analyzed results showed that, as the amount of ZrO2 increasing, the dielectric constant and temperature dependence of dielectric constant of this ceramic both decreased, while its dielectric tunability kept high value.

Abstract: In this work, BST (x=0.7, 0.5, 0.3) films have been deposited onto Nb-SrTiO3 substrate with pulsed laser deposition. The crystal structure and surface morphology have been characterized by X-ray diffraction (XRD) and atomic force microscopy, respectively. XRD results revealed that in certain elaboration condition the films were aligned along (00l) direction, normal to the substrate surface. The dielectric loss, relative dielectric permitivity, and polarization of BST films strongly depended on Sr content at room temperature. The tunability of relative dielectric permitivity of BST films exhibited strongly dependence on Sr content, and BST-0.5 shows the maximun K (K = tunability/loss) value.

Abstract: Barium strontium titanium oxide (BSTO) has great advantages and potentiality for the application of microwave technology. In order to be used in phased array antennas, high dielectric tunability, relatively low dielectric constant and low dielectric loss are required. In this paper, MgO was mixed into BSTO and the microstructure and dielectric properties of MgO-mixed BSTO bulk ceramics were investigated. The mole ratio of Ba and Sr was rather fixed to 5:5 in this study. It is observed that a small amount of MgO (5 wt%) has gone beyond the solubility limits of Mg in BSTO. The dielectric constant and dielectric loss of BSTO ceramics decreased with the increase of the content of MgO mixed. However, the tunability of MgO-mixed BSTO ceramics decreased at the same time. 20wt% MgO-mixed BSTO ceramics exhibits preferable dielectric properties with acceptable tunability.

Abstract: In this paper, a microwave material (Ba0.85Ca0.15)0.5Sr0.5TiO3 with 5 wt% MgO additive was prepared by traditional solid-state reactions, i.e., mixing BaTiO3 and SrTiO3 powders and then doping CaTiO3 and MgO. It was found that, with the increasing CaTiO3 content, the dielectric constant of the resultant material decreases and the tunability and dielectric loss increase.

Abstract: (Zr0.8Sn0.2)TiO4 ceramics with additives of ZnO, CuO, Bi2O3 and MnCO3 were prepared by the conventional mixed oxide route. They were characterized by TG/DTA, SEM, EDS and a network analyzer. Microwave properties of (Zr0.8Sn0.2)TiO4 ceramics were investigated as a function of the amount of additives. The optimal values of dielectric constant er, quality factors Q*f and temperature coefficient of resonant frequency tf reached 35, 51000 GHz and 26 ppm/°C respectively with 2.0 wt% MnCO3. Specimens with additives of ZnO, CuO and Bi2O3 had microwave properties of er = 35 ~ 39, Q*f = 9000 ~ 35000 GHz and tf = 15~40 ppm/°C.

Abstract: Sr(Bi1-xSmx)8Ti7O27 ceramics were prepared by Sm2O3-substitution for Bi2O3 through solid-state reaction route. The dielectric properties of the sintered bodies such as er, Q and tf were investigated. The ceramics were characterized by SEM, XRD, DTA and TG, which behaved high dielectric constant of 128 ~154 at the frequency of 10 GHz.

Abstract: BST/PLT composite thick films with various content of PbO-B2O3 glass additive from 5mol% to 25mol% were successfully prepared by screen-printing the paste onto alumina substrates. XRD, SEM and impedance meter were used to analyze the phase structures, morphologies and dielectric properties of the thick films. The results showed that the BST phase has no interaction with PbO-B2O3 glass in the composite thick films at 750 oC. Diffusion between PLT phase and PbO-B2O3 glass phase occurs and the c axis of PLT phase in thick films reduces slightly. The high infiltration between the glass phase and particles densify the composite thick films and the uniform microstructure can be obtained in the thick films with PbO-B2O3 glass additive content of 10mol%. Good temperature stability of dielectric properties is achieved with the 25mol% content of PbO-B2O3 glass additive and the variance of the relative dielectric constant in the temperature range between 0oC and 300oC is 15%.

Abstract: Silver dispersed lead titanate films were prepared with different Pb/Ti ratio precursors. The influence of lead excess in precursor on the formation and dielectric properties of silver-dispersed lead titanate film was investigated. Firstly, Pb excess in precursor will eliminate the formation of pyrochlore PbTi3O7 and increase c/a ratio of perovskite PbTiO3. Secondly, excessive Pb will react with silver, and they can produce volatile product, which evaporate during heat treatment process. The volatility of the reaction product varies with the increase in lead excess. When lead excess is low (Pb/Ti=1.1), volatility of reaction product is high. At this time, only small amount of silver remain in the film. The remanent silver aggregate to form small silver particles. When lead excess is high (Pb/Ti=1.2 and Pb/Ti=1.3), volatility of reaction product gradually becomes poor. At this time, the content of remanent silver in the film increase with the increase in lead excess. Compared with the film prepared with low Pb/Ti ratio, the dispersive degree of silver in film prepared with high Pb/Ti ratio is higher. Due to the decrease of remanent silver content in the film, dielectric constant and dissipation factor both decrease when Pb/Ti initially increase from 1 to 1.1. And after that, dielectric constant and dissipation factor both increase with the addition of excessive Pb in precursor, due to the increase in the content and dispersion degree of silver, and increase in c/a ratio of PbTiO3 lattice with the addition of excess Pb. The film prepared with appropriate excessive lead (Pb/Ti=1.3) precursor expresses higher dielectric constant and lower dissipation factor than the film prepared with stoichiometric Pb/Ti ratio.