Papers by Keyword: Microwave Ceramic Dielectric

Abstract: Bi₂Ti₂O₇ microwave dielectric ceramics were synthesized by a modified sol-gel method using citric acid as metal chelating agent. The thermal decomposition behavior of the as-prepared precursor was characterized by XRD technique. The effects of the amount of citric acid and the molar ratio of bismuth nitrate to tetrabutyl titanate on the crystal structure of Bi₂Ti₂O₇ were also investigated. XRD results showed that well-crystallized Bi₂Ti₂O₇ powders could be synthesized by calcining the precursor at 550 °C as the molar ratio of CA to Bi was 1:1. Moreover, non-stoichiometric ratio of Bi to Ti was required to form the pure Bi₂Ti₂O₇ phase. However, Bi₄Ti₃O₁₂ and Bi₂Ti₄O₁₁ second phases were formed after sintering process. At 1150 °C, only the sample doped with 3 wt% Ho³⁺ showed a single pyrochlore structure, which exhibited good microwave dielectric properties with a high ε_r of 115.02, a Q × f of 1,515 GHz, and a τ_f of 30 ppm/°C.

Abstract: In this work, the microwave dielectric ceramic (1-m)(Mg_0.8Zn_0.2)TiO₃·m{Ba₄Nd_28/3Ti₁₈O₅₄·0.18Bi₂O₃}(m=0.1~0.4)(MZT-BNT) was studied to improve dielectric properties. The results of the dielectric properties, density, XRD and SEM show that the value of m and the sintering temperature affected the structure and properties of the ceramics. MZT-BNT composite system is a two-phase composite system. With the adding of BNT, the dielectric properties of MZT increase significantly. As m value increases, the bulk density and the dielectric constant of the composite system increase, while the quality factor reduces and the temperature coefficient of resonant frequency is close to zero. The dielectric properties of MZT-BNT sintered at 1200 °C (m = 0.3) are ε_r = 34.03, Q_f = 7177 GHz,τ_f = -3.39 ppm/°C, respectively.

Abstract: By means of 34.5 GHz millimeter-wave (MMW) sintering, BaO-Nd2O3-TiO2 microwave ceramic dielectric was prepared from nano-particles of the xBaO×(0.35-x)Nd2O3×0.65TiO2 ternary compound, which possess fine grain, low porosity and good dielectric characteristics. The materials which have ultra-low dielectric loss can be fired by MMW heating at very high frequency, which is unable to be done by normal microwave heating at 2.45 GHz. The sintering temperature is 160 ~ 400°C lower than that of normal firing. The ceramic sample consists of the main phase of Nd2Ti2O7 with perovskite-like layer structure (PLS) and the secondary phase of BaNd2Ti4O12 (Ba4.5Nd9Ti18O54)with perovskite-like tungsten bronze structure, being the same as the results from normal sintering. The excellent microwave characteristics were observed.