Investigation On Modification Of ZnO-TiO₂ System Microwave Dielectric Ceramics

With the rapid development of microwave communication technology, high performance microwave dielectric ceramics, which can be sintered at low temperature, are required by the miniaturization of microwave components. In the zinc titanate ceramics, zinc metatitanate behaves excellent microwave dielectric properties, high dielectric constant, high quality factors and stable temperature coefficient of resonant frequency, and it can be sintered at lower temperature (1100℃) than traditional microwave dielectric ceramics. So this system microwave dielectric materials may be put into industrial production quickly. But zinc metatitanate, ZnTiO₃, decomposes into zinc orthotitanate and rutile at 945℃, the preparation of pure ZnTiO₃ has been unsuccessful by conventional solid-state reaction. Enhancing the thermal stability of zinc metatitanate, is the key to prepare low temperature co-fired microwave dielectric material with the excellent microwave dielectric properties. To this question, some studies will be carried out as follows.After the synthesis thermal analysis to the raw material of the zinc titanate ceramics, and has preliminary determined the sintering temperature curve of the zinc titanate ceramics, the phase transition temperature of zinc metatitanate was 950℃. The microstructure of this ceramics, which sintered at different temperature or different molar ratios of Ti/Zn, was studied by X-ray diffraction analysis and scanning electron microscopy, and it was found that the optimum temperature of synthesizing zinc metatitanate at approximately 850℃, and the specimens have optimum of synthesizes zinc metatitanate when the molar ratio of Ti/Zn is 1:1.Using the similar ionic radius Mg²⁺and Co²⁺ substituting the Zn²⁺ of zinc titanate, where Zn²⁺at the A-site of ilmenite-type titanates. The microstructure of this ceramics, which has different amounts of additions, was studied by X-ray diffraction analysis and scanning electron microscopy, and it was found that the phase transition temperature of zinc metatitanate was increased for 70℃; the proper amounts of double ionic substitution can enhance the thermally stable temperature of zinc metatitanate crystals, and also decreased the grain size of zinc metatitanate crystals, and increased the densification of zinc metatitanate ceramics. After systematic studies, we have achieved microwave dielectric material Zn_0.93(Mg_1/2Co_1/2)_0.07TiO₃ possessing excellent properties which can be sintered at approximately 990℃. The dielectric properties of the samples are indicated as below: dielectric constant values saturating at 25, the Qf value being 40000GHz, the temperature coefficient of resonant frequency being 0 ppm/℃_-1.The ionic radius of Zr₄₊and Sn_{4^</sub> are very similar to the ionic radius of Ti4+, using the similar of ionic radius Zr⁴⁺or Sn⁴⁺ substituting Ti⁴⁺of Zinc metatitanate, where Yi⁴⁺ at the B-site of ilmenite-type titanates. The microstructure of this ceramics, which has different amounts of additions, was studied by X-ray diffraction analysis and scanning electron microscopy, and it was found that the solubility limit of zirconium ions in ZnTiO3 was close to 0.05, The solubility limit of stannum ions in ZnTiO3 was same, The proper amounts of Zr4+or Sn4+ ionics substitution all can increase the phase transition temperature of Zinc metatitanate for 40℃, and changes the microstructure of the zinc titanate ceramics. After systematic studies, we have achieved microwave dielectric material ZnTi0.97Zr0.03O3 possessing excellent properties which can be sintered at approximately 1150℃. The dielectric properties of the samples are indicated as below: dielectric constant values saturating at 29.5, the Qf value being 3620GHz, the temperature coefficient of resonant frequency was 43 ppm/℃^-1; we also achieved microwave dielectric material ZnTi0.95Sn0.05O3 possessing excellent properties which can be sintered at approximately 1100℃. The dielectric properties of the samples are indicated as below: dielectric constant values saturating at 29.75, the Qf value being 4539GHz, the temperature coefficient of resonant frequency being 21 pprn/℃^-1.}