Synthesis And Properties Of MgTiO₃-based Microwave Dielectric Ceramics

With the rapid development of microwave communication and radar technologies, many researchers have focused on the microwave dielectric materials which applied in the x-band (8to12GHz), with high Q value and near-zero temperature coefficient of resonant frequency. The MgTiO3microwave dielectric ceramic with low dielectric loss, abundant raw materials source and low cost, the resonant frequency of which is about10GHz, has attracted much attention. However, the ceramic system has some disadvantages such as high sintering temperature, narrow sintering range and large negative τf. In order to improve the disadvantages, in this thesis, on the basis of high pured MgTiO3powers synthesized by traditional solid phase reaction method, through the ways such as two phase composite, ion doping, adding sintering additives, the sintering characteristic and microwave dielectric properties of MgTiO3based ceramic have been investigated. The main results are as follows:The effects of presintering temperature, sintering temperature time, molar ratio of Mg/Ti on the MgTiO3power were investigated. The results show that high pured MgTiO3powers were synthesized when the molar ratio of Mg/Ti was1.03and the power was calcinated at1100℃for4h in air atmosphere. The sintering characteristics and microwave dielectric properties of MgTiO3, MgTiO3-SrTiO3(MST) ceramics synthesized by the conventional solid-state method were investigated. The results show that high pured MgTiO3power synthesized by traditional solid phase reaction may include MgO which is be beneficial to promote the ceramic sintering and improve the sintering characteristic and microwave dielectric properties of MgTiO3ceramic. The MgTiO3ceramics sintered at1320℃for4h exhibited excellent dielectric properties: εr≈17.91, Q·f≈150000GHz, τf≈-49.59ppm/℃. SrTiO3addition can adjust the τf value of MgTiO3. When the amount of SrTiO3addition is up to6.0wt%, the τf value of MST ceramics can achieve near zero. The MgTiO3-6.0wt%SrTiO3(MST0.06) ceramics sintered at1275C for4h were excellent dielectric properties: εr≈20.76, Q·f≈50000GHz. τf≈0.38ppm/℃.The effects of Zn2+, Co2+doped and sintering aids B2O3on the sintering characteristic and microwave dielectric properties of MST0.06were investigated. The results show that proper ion doping (Zn2+, Co2+) can effectively to promote the ceramic sintering, lower the sintering temperature and improve the microwave dielectric properties of MST0.06ceramics. When the amount of Zn2+, Co2+ion doping is0.05and2.0wt%, The MSTO.06ceramics sintered at1250℃for4h obtained excellent dielectric properties: εr≈=21.09, Q·f≈53000GHz, τf≈3.37ppm/℃. εr≈21.26, Q·f≈52000GHz, τf≈1.68ppm/℃, respectively. The proper sintering aids B2O3effectively promote the ceramic densification and lower the sintering temperature and don’t deteriorate the microwave dielectric properties of MSTO.06ceramics. Excellent dielectric properties of the ceramics sintered at1225℃for4h are: εr≈20.76, Q·f≈50000GHz, τf≈0.38ppm/℃.