| The rapid development of new communication systems such as mobile multimedia systems, ultrahigh speed wireless local area network and intelligent transport systems required highly qualified microwave dielectric ceramics. It was desirable to adopt new materials research method. Recently, as a new synthesis route, soft chemistry method has received considerable attention. However, there were very few reports on the soft chemical syntheses of CaTiO3-based microwave dielectric ceramics. To my knowledge, there was no report on the synthesis of CaTiO3-based microwave dielectric ceramics by the polymeric precursor method.The dissertation relies on the Chinese National High-Tech Project "Investigation and Preparation of New Microwave Dielectric Ceramics Materials and Devices" under Grant No.2001AA-ZB3201 and the important research item of science and technology "Investigation and Preparation of High εr Microwave Dielectric Ceramics and Components " (Contract No. Important 0206) supported by the Ministry of Education, P. R. China. Under the guidance of materials design, in order to investigate the relationship among the three microwave materials parameters, which are εr, Qf and τf, and to prepare high performance CaTiO3-based microwave dielectric ceramics, using XRD, DTA, TG, SEM, TEM and FTIR, the composition and the processing technique of CaTiO3-based microwave dielectric ceramics were tailed. Especially, the preparation of CaTiO3-based microwave dielectric ceramics via polymeric precursor method were studied. The main results are as follows.The CaTiO3 microwave ceramics was prepared by the solid-state reaction method. The ceramics sintered at 1300℃ for 3 h showed microwave properties with εr of 170, Qf of 4800 GHz and τf of +810 ppm/℃.It is the better choice to obtain CaTiO3-based temperature stable microwave dielectric ceramics with high εr by combining CaTiO3 with microwave materials, which have relatively high εr and negative τf such as Li1/2Ln1/2TiO3. One of the important methods to prepare low loss CaTiO3-based microwave dielectric ceramics was to combine CaTiO3 with microwave materials, which have low dielectric loss and negative τf such as rare-earth aluminates. The effects of Ln3+ substitution on the microwave dielectric properties of CaTiO3 and the relationship between τf and the tolerance factor t were studied. For Ca1-xLa2x/3TiO3 ( x = 0.1, 0.4, 0.5 ) materials, when x = 0.4, sintered at 1350℃ for 4 h , the ceramics showed microwave properties with εr of 118, Qf of 10360 GHz and τf of +295 ppm/℃. For Ca1-xNd2x/3TiO3 ceramics with x = 0.39, sintered at 1350℃ for 4 h , showed microwave properties with εr = 109, Qf >8500 GHz. The τf of Ca1-xLa2x/3TiO3 ceramics decreases with increasing x, which can be explained by the changes of tolerance factor t. The onset of octahedral tilting is controlled by the tolerance factor. The τε increases with the decreases of t, therefore, τf decreases with the increases of x。The microwave dielectric properties of (1–y)Ca1-xLn2x/3TiO3–yLi1/2Nd1/2TiO3( Ln = La, Nd, Sm)were studied by solid-state reaction method. For Ln = Sm, y = 0.3, the sample calcined at 1050℃, sintered at 1300℃ for 3 h showed microwave properties with εr of 92, Qf of 5060 GHz and τf of 7.5 ppm/℃. Compared with the Ln = La, Nd materials families, this materials family showed the best microwave properties.Three methods to prepare CaTiO3-based microwave dielectric ceramics via polymeric precursor method were studied, which were the combination of ethylenediaminetetraacetic acid (EDTA) and ethylene glycol(EG), the combination of citric acid(CA)and EG and using EDTA as a chelating agent (no use of EG).The syntheses of rare-earth aluminates LnAlO3 and (1–y)CaTiO3–yNdAlO3(CTNA)(y = 0.3)of low loss CaTiO3-based microwave ceramic powders were studied by using EDTA / EG combination. As an example, single phase LaAlO3 with perovskite structure was found to crystallize directly from an amorphous precursor at 750℃ for 2 h in air, without intermediate phase formation. T...
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