Key Engineering Materials Vols. 336-338

Abstract: The effects of CuO and V2O5 addition on sintering behaviors and microwave dielectric properties of 0.7Ca2P2O7-0.3TiO2 ceramics were investigated. With CuO and V2O5 addition, the sintering temperature of 0.7Ca2P2O7-0.3TiO2 can be effectively reduced from 1150 to 950oC. The dielectric constant of the low fired 0.7Ca2P2O7-0.3TiO2 ceramics was not significantly changed while the quality factor was affected by additives. The temperature coefficient of resonant frequency value was increased in negative value with the additive contents. V2O5 and CuO additives effectively improved the densification and dielectric properties of 0.7Ca2P2O7-0.3TiO2 ceramics. The correlation between the phase constituents and the dielectric properties was investigated with additive contents.

Abstract: (PbySr1-y)ZnxTi1-xO3-x thin films were prepared on ITO/glass substrate by sol–gel process using dip-coating method. The phase structure, morphology, and dielectric properties of thin films were investigated by XRD, SEM and impedance analyzer, respectively. The perovskite phase structure was exhibited in the Zn-doped PST thin films. The formation ability of the thin films of the perovskite phase and its grain size decreased with the increase in doping Zn. The dielectric constant of the thin film was influenced by oxygen vacancies which could be controlled by Zn doping.

Abstract: (1-x)(Ca0.61Nd0.26)TiO3-x(Li0.5Sm0.5)TiO3 (0.2 ≤ x ≤ 0.7) ceramics were prepared by solid-state reaction method and the microwave dielectric properties of the resultant materials at different (Li0.5Sm0.5)TiO3 contents were investigated. A single phase of perovskite in all samples was confirmed by XRD patterns. With increasing (Li0.5Sm0.5)TiO3 content, Q×f value and dielectric constant (εr) decrease slightly and the temperature coefficients of the resonant frequency (τf) of the specimens decreases noticeably. The optimum parameters, i.e.,εr = 109, Q×f = 5259 GHz and τf = ~0 ppm/°C, for the composition of 0.4(Ca0.61Nd0.26)TiO3-0.6(Li0.5Sm0.5)TiO3 was obtained when keep the calcination temperature at 1250°C for 3 h.

Abstract: The microstructures and microwave dielectric properties of temperature compensated composite ceramics (1-x)(Na0.5La0.5)TiO3+xCeO2 doped with 1wt%CuO were investigated. Dense and mixed phase samples were produced in the range of 0.1 ≤ x ≤ 0.9. As x value increases the Qf increases nonlinearly while the dielectric constant decreases almost linearly. The compensated τf value is obtained in 0.1(Na0.5La0.5)TiO3 + 0.9CeO2 + 1wt%CuO ceramic with the Qf and εr being 8240GHz and 32.0 respectively.

Abstract: (1-x) Ca2/5Sm2/5TiO3-x Li1/2Nd1/2TiO3 (CSLNT) ceramics, suitable for use in resonators or filters at microwave frequency, have a high εr and a low temperature coefficient of resonant frequency. The effects of calcinations on the microwave dielectric properties of CSLNT were studied. The CSLNT (x = 0.3) ceramics sintered at 1300oC for 3 h showed microwave properties with εr of 92, Qf of 5060 GHz and τf of 7.5 ppm/oC. The microwave dielectric properties of CSLNT (x = 0.3) ceramics were also improved by soft chemistry methods such as citric acid gel route and ethylenediaminetetraacetic acid (EDTA) chelating method. The excellent microwave properties with εr = 96, Qf = 6290 GHz and τf = 6 ppm/oC were obtained by EDTA chelating method for CSLNT (x = 0.3) ceramics.

Abstract: Zinc titanate ceramics having excellent dielectric properties and low sintering temperature are promising materials for RF/microwave multilayer devices. In this paper, the ZnO-V2O5 addition was added to promote the sintering process in order to obtain low-temperature sintered ceramics with high quality factors. The sintering addition could also restrain ZnTiO3 phase from decomposition. Using this method, low-temperature sintered zinc titanate ceramics with excellent microwave dielectric properties of εr~ 25.3, Q×f~15200GHz, and τf ~ -16 ppm/oC were obtained at sintering temperature of 800oC. The low-fired mechanism, microstructure, phase formation and microwave dielectric properties of ceramics were investigated by XRD, SEM, EDS and network analysis techniques, respectively.

Abstract: The effect of V2O5 as additives of different content on the densification, microstructure and dielectric properties of Ba(Mg1/3Nb2/3)O3 (BMN) was investigated. The sintering temperature of the V2O5-doped BMN samples were lowered down to 1250 oC with 0.5wt% V2O5 compared to pure BMN ceramics where the sintering temperature was 1500 oC at least. The εr and τf was not influenced much, while the Q value was affected by the sintering temperature and the V2O5 additives. The Q value decreased with decrease of the sintering temperature and the V2O5 addition increasing due to the bulk density and the second phase. Good microwave dielectric properties of Q·f=42100GHz, εr =31.7 and temperature coefficient of resonance frequency (τf) =22.7ppm/ oC were obtained with 0.25 wt% V2O5 sintered at 1350 oC for 4h.

Abstract: Microwave dielectric ceramics of CaO-2ZnO-xTiO2 (x=6~9) were prepared by citrate sol-gel method. The phase formation and structural properties of the ceramics were investigated as a function of titania content (x). Monophase of Ca2Zn4Ti16O38 polytitanates were formed at x = 8. With the increase of x, residual rutile phase were observed, whereas with the decrease of x, the CaTiO3 and Zn2TiO4 phases were detected. The microwave dielectric properties of the sintered ceramics were investigated using resonance method. The variation of dielectric properties of the ceramics as a function of titania content (x) was investigated. For the monophase of Ca2Zn4Ti16O38 polytitanate at x = 8, the dielectric properties showed minimum dielectric constant of 48.1, minimum temperature coefficient of resonant frequencies +44.1 ppm/oC, and maximum Q×f value of 31000 (at 6.921GHz). Deviating from x = 8, the dielectric constant and temperature coefficient of resonant frequencies slightly increased, and the Q×f value decreased. The variation was concerned with the presence of secondary phase.

Abstract: This paper presents the microwave dielectric property of porous silicon nitride ceramics at a frequency of 9360 MHz, which were fabricated by the nitridation of silicon powder. The porous ceramics with different volume fraction of porosity from 18.6% to 56.2% were produced by adding different amount of the pore-forming agent into the initial silicon powder. Microstructural analysis revealed a dense matrix containing large pores and cavities with needle-shaped and flaky β-Si3N4 grains distributing in it. The results showed that the dielectric constant of the ceramics reduces with the porosity increases. With the addition of α-Si3N4 powder in the raw silicon powder, the nitridation rate is raised, and the dielectric constant and the dielectric loss of the ceramics decrease notablely.

Abstract: SiC-AlN solid solution powders were prepared from the mixtures of aluminum, silicon and carbon black in a nitrogen atmosphere with preheating self-propagating high temperature synthesis (SHS) method. The powders synthesized with different ratios of Al/Si were mixed with paraffin wax and the microwave permittivity of the mixtures was measured at the frequency of 8.2~12.4GHz. The results were contrasted with that of SiC powders synthesized by preheating SHS in argon and nitrogen atmosphere respectively. The ε′, ε″, and the tgδ (ε″/ε′) of the mixture of SiC prepared in a nitrogen atmosphere are highest, followed with those of the SiC-AlN solid solution powders and the SiC powders prepared in an argon atmosphere. Along with the increase of atomic ratio of Al/Si, the ε′, ε″, and tgδ of SiC-AlN solid solution decrease. We believe that, with the increase of AlN dissolved, the concentration of carriers and the effect of dielectric relaxation will decrease because of the two contrary dopants.