Development And Application Of Microwave Dielectric Ceramics Based On The Principle Of Microwave Energy

In this thesis, in the view of the synthesis materials,Ba₅(Nb_0.85Sb_0.15)₄O₁₅ Ca_0.65Ti_0.65La_0.35Al_0.35O₃ ceramics were prepared via conventional mixing oxide route, and the effects of sintering aid and processing factors on chemical structure and dielectric properties of the samples were systematically investigated. In addition, in the view of the device design and manufacturing techniques, different kinds of microwave dielectric ceramics, including MgTiO₃-CaTiO₃, Ca_0.65Ti_0.65La_0.35Al_0.35O₃, Ba(Mg_0.2/3Zn_0.8/3Nb_2/3) and BaO-La₂O₃-TiO₂ ceramics were explored for the applications of mobile communication and microwave heating based on the principle of microwave energy.Chemicals of H₃BO₃, MnCO₃ and CeO₂ were used as sintering additives to lower the sintering temperature for Ba₅(Nb_0.85Sb_0.15)₄O₁₅, i.e.,BSN, ceramics. The sintering behavior, microstructure and microwave properties were investigated by XRD, SEM and network analyzer. With 1lwt% H₃BO₃ and 0.15wt% MnCO₃ addition, the BSN ceramics sintered at 940℃get excellent microwave dielectric properties of anε_rvalue of 29.28, a Q×f value of 17,113GHz, and aÏ„_f value of +10.34ppm/℃. Microwave dielectric properties are adjusted for the ceramic Cao.65Tio.65Lao.35Alo.35O3 + lwt% H₃BO₃ + 0.15wt%-0.75wt%CeO₂ sintered between 900℃and 940℃for 2 h, with values of Q×f≈16,000-23,000GHz,ε_r≈28-31 andÏ„_f≈+8⁺18ppm/℃.The influence of CuO and MnCO₃ additives on the sinterability, microstructure and microwave dielectric properties of Ca_0.65Ti_0.65La_0.35Al_0.35O₃, i.e., CTLA, ceramics was investigated. The results indicated that the density and dielectric properties of CTLA ceramics could be improved by both low-level doping of CuO (up to 1 wt%) and MnCO₃ (up to 0.75wt%). The sintering temperature of CTLA ceramics with addition of CuO/MnCO₃ could be effectively reduced from 1450℃to 1320℃due to the liquid phase effects. Excellent microwave dielectric properties were achieved for the ceramic Ca_0.65Ti_0.65La_0.35Al_0.35O₃ + 0.75wt% CuO/MnCO₃ sintered at 1320℃for 2 h, with values of Q×f≈32,800GHz,ε_r≈43 andÏ„_f≈+10ppm/℃.Meanwhile, gel-casting forming process was successfully used to fabricate microwave ceramic substrates. The dielectric properties of MgTiO₃-CaTiO₃ ceramics prepared by gel-casting were compared with those by dry press forming. In addition, two kinds of microwave antennas were also developed with the gel-casting forming process.A new method was presented for calculating frequency and Q-factor of dielectric resonator. A novel laser trimming procedure was utilized to adjust the frequency of practical ceramics for dielectric resonators aiming better performance. Experimental results showed that the resonant frequency increased after laser etching applied on either upper or lower surface of resonator; meanwhile, the Q-factor of dielectric resonator was improved.Finally, some results, such as BaO-La₂O₃-TiO₂,Ba(Mg_0.2/3Zn_0.8/3Nb_2/3) and MgTiO₃-CaTiO₃ ceramics were applied for microwave products supported by the National High-Tech Research and Development Plan of China (Plan 863) under Grant No. 2001AA325100.