Doping Modofication Of （Mg,Ca）TiO₃ System Microwave Dielectric Ceramics

MgO-SiO2-TiO2-CaO microwave materials were prepared by adding Mg2SiO4 into MgTiO3-CaTiO3 system.This material has low dielectric constant and high quality factor which was widely used in producing dielectric resonate and high-frequency capacitor.In this paper,on the base of MgTiO3-CaTiO3 system,the process paramaters of producing Mg2SiO4 was studied and Mg2SiO4-CaTiO3-MgTiO3(MSTC)composite ceramics were prepared.The effect of component ratio,phase transition,and addition of MnCO3 and Nb2O5 on the physical and dielectric properties of the MSTC ceramics was investigated.The main research contents were as follows:1.Using Mg(OH2)-4MgCO3-5H2O and SiO2 as raw material,Mg2SiO4 was prepared by solid state synthesis process.The optimum process of preparing Mg2SiO4 was obtained by adjusting Mg/Si molar ratio,ball milling process and sintering temperature.The obtained Mg2SiO4 powders was crushed by ball milling process,and the effect of ball milling time on ball milling efficiency was studied.The results showed that the milling efficiency of ball mill tank with rubber lining was lower than that of ceramic lining,the milling efficiency of 1000ml ball milling tank was lower than that of 250 ml.The pure Mg2SiO4 was prepared by sintering the mixed powders at 1350 ℃,which was obtained by milling for 6 h in 250 ml ball milling tank with Mg/Si=2.05～2.1.The Mg2SiO4 ceramic which was sintered at 1 300～1360 ℃ for 3 h showed better dielectric properties with ε r=7.4±0.05 and tan δ=7.5 ×10-4 under 1 MHz.2.Mg2SiO4-CaTiO3-MgTiO3(MSTC)composite ceramics have been prepared by conventional solid state reaction method.The effects of Mg2SiO4 addition amounts on the microstructure and dielectric properties of Mg2SiO4-MgTiO3-CaTiO3(MSTC)composite ceramics have been investigated.The results indicated that the sintering temperature of MgTiO3-CaTiO3 based ceramics with Mg2SiO4 addition could be lowered effectively to 1320～1 34℃,and the dielectric constant decreased and dielectric loss increased gradually with the increase of Mg2SiO4 content.The ceramics containing 45 wt%Mg2SiO4 sintered at 1340 ℃ showed excellent dielectric properties with εr=13.3 and tanδ=4.5×10-4.3.The original magnesium titanate powders was calcined by pre-sintering process,andthe 0.45Mg2SiO4-0.05CaTiO3-0.55MgTiO3(0.45MS)ceramic was prepared by solid synthesis process using original magnesium titanate and calcined magnesium titanate as raw materials.The results showed that pure phase of MgTiO3 was obtained when magnesium titanate powders was calcined at 1300 ℃ for 2 h.The MgTi2O5 phase was vanished and the dielectric properties of 0.45MS ceramics prepared from calcined magnesium titanate was better than that prepared from original original magnesium titanate.The 0.45MS ceramic sintered at 1340 ℃ for 2 h exhibited excellent dielectric properties with ε r=14.3 and tan δ=4.0×10-4.4.Mg2SiO4-CaTiO3-MgTiO3(0.45MS)based microwave dielectric ceramics were prepared by solid state method.The effects of MnCO3 and Nb2O5 addition on the dielectric properties of 0.45MS ceramics were investigated.The results indicated that Mn2+ could replace Mg2+ to form(Mg,Mn)TiO3,and the 0.45MS ceramics with 5wt‰ addition exhibited dielectric properties with εr=14.4 and tan δ=3.8×10-4.Whereas,Nb5+ could enter into MgTiO3 and replace Ti4+ to form MgNb2O3.67.The 0.45MS ceramics with 4wt‰ Nb2O5 addition showed excellent dielectric properties with εr=13.9 and tan δ=3.6×10-4.