Search

High-Q and temperature-stable 0.63SrTiO3–0.37LaAlO3 (63ST–37LA) ceramic with different mole ratio of Na2SiO3·9H2O/MgO (Si/Mg) was produced by the solid-phase method. The effect of Si/Mg mole ratio (the value of Si/Mg mole ratio referred to R) on the phase transformation, sintering, and dielectric characteristics of 63ST–37LA ceramic was researched. X-ray diffraction and Rietveld refinement proved that a cubic perovskite structure of SrTiO3-based solid solution with a Pm-3m space group was formed. Scanning electron microscopy proved that appropriate amount of Na2SiO3·9H2O/MgO could promote the grain growth and generate a compact and uniform microstructure, so high relative density and quality factor (Q·f) value were achieved. When R was 0.53 and the addition of MgO was 2 mol%, the sintering temperature decreased by 200 °C and Q·f value increased by 44%, and outstanding dielectric characteristics with εr of 45.97 ± 0.35, Q·f value of 69,928 ± 1850 GHz, τf value of 1.7 ± 0.8 ppm/°C were achieved for 63ST-37LA ceramic at 1350 °C. [ABSTRACT FROM AUTHOR]

ZnO-Al2O3-MgO-SiO2-TiO2-CaO (ZnO-based) linear resistance ceramics were prepared by the conventional ceramics method with different amounts of CaO. The impact of CaO doping on the phase composition, microstructures and electrical properties of ZnO-based linear resistance ceramics was investigated in detail. The research showed that CaO doping not only limits the growth of ZnAl2O4 and ZnO grains—in particular, the grain size of ZnAl2O4 decreased from 4.40 μm to 1.38 μm—but also improves the electrical properties. The grain boundary barrier height and nonlinear coefficient decreased with the increase in CaO content, and the resistance temperature coefficient increased from −5.65 × 10−3/°C to 1.04 × 10−3/°C. The 4.00 mol.% CaO-doped ZnO-based linear resistance ceramics were found to possess excellent electrical properties: the resistivity is 44.87 Ω cm, the grain boundary barrier height is 0.011 eV, the nonlinear coefficient is 1.05 and the resistance temperature coefficient is −0.822 × 10−3/°C, a stable resistivity against frequency. [ABSTRACT FROM AUTHOR]

(1−x)(Ca0.88Sr0.12)TiO3–x(Bi0.5Na0.5)TiO3 (CST–BNT, x = 0, 0.025, 0.05, 0.075, 0.10) high dielectric constant ceramics were prepared by the solid state reaction method, and the effects of (Bi0.5Na0.5)TiO3 (BNT) on the sintered properties, phase composition, microstructures, and dielectric properties of (Ca0.88Sr0.12)TiO3 (CST) ceramics were investigated as a function of the x-value and sintering temperature. The results showed that: BNT had no obvious influence on phase composition of CST ceramics, and the single phase solid solutions were obtained throughout the studied compositional range. Adding a moderate amount of BNT not only effectively lowered the sintering temperature from 1400 to 1275 °C, but also improved the sintered properties and the dielectric properties, especially that the τf decreased from + 942 to + 639 ppm/°C, which was decreased by about 32%. For x = 0.05, the 0.95(Ca0.88Sr0.12)TiO3–0.05(Bi0.5Na0.5)TiO3 ceramics sintered at 1275 °C for 3 h exhibit an excellent combination of microwave dielectric properties: εr = 185.5, Q × f = 8116 GHz and τf = + 639 ppm/°C, and which could be used as a promising candidate to equalize the materials with negative temperature coefficient of resonant frequency. [ABSTRACT FROM AUTHOR]

0.6ZrO-0.4(ZnNb)O-TiO(ZN40) microwave dielectric ceramics were prepared by conventional solid-state reaction method, and the effects of LiCO, CuO, MnCO additives doping on their microstructures, phase composition, and dielectric properties were investigated. The results shown that suitable additives didn't change the crystal phase of ZN40 ceramics, and the main crystalline phase of all the samples was orthorhombic α-PbO type ZrTiO; a moderate amount of LiCO, CuO, MnCO could not only effectively lower the sintering temperature due to form liquid-phase, or promote ion diffusion by Ti-site ionic substitution of unequal values, but also improve the quality factor ( Q × f). The optimal integrated microwave dielectric properties( ε = 42.59, Q × f = 52,500 GHz and τ = +7.8 ppm/°C) were achieved for ZN40 ceramics containing 1 wt% MnCO sintered at 1220 °C for 3 h, and which make this material a prospective candidate for use in satellite communication and mobile communication base station. [ABSTRACT FROM AUTHOR]

Fused silica ceramics were fabricated by gelcasting, by use of a low-toxicity N′ N-dimethylacrylamide gel system, and had excellent properties compared with those obtained by use of the low-toxicity 2-hydroxyethyl methacrylate and toxic acrylamide systems. The effect of sintering temperature on the microstructure, mechanical and dielectric properties, and thermal shock resistance of the fused silica ceramics was investigated. The results showed that sintering temperature has a critical effect. Use of an appropriate sintering temperature will promote densification and improve the strength, thermal shock resistance, and dielectric properties of fused silica ceramics. However, excessively high sintering temperature will greatly facilitate crystallization of amorphous silica and result in more cristobalite in the sample, which will cause deterioration of these properties. Fused silica ceramics sintered at 1275°C have the maximum flexural strength, as high as 81.32 MPa, but, simultaneously, a high coefficient of linear expansion (2.56 × 10/K at 800°C) and dramatically reduced residual flexural strength after thermal shock (600°C). Fused silica ceramics sintered at 1250°C have excellent properties, relatively high and similar flexural strength before (67.43 MPa) and after thermal shock (65.45 MPa), a dielectric constant of 3.34, and the lowest dielectric loss of 1.20 × 10 (at 1 MHz). [ABSTRACT FROM AUTHOR]