Study On Preparation And Performance Of TiO₂ Based Microwave Ceramics

The whole machine products in the microwave communication industry are devel-oping towards portability and miniaturization,and there is a higher demand for the minia-turization of microwave components.Miniaturization of devices requires microwave ce-ramics with high dielectric constants.TiO₂has been widely studied due to its wide source and low price among microwave ceramics with high dielectric constant.Although TiO₂has a relatively high dielectric constant,However,there is a Ti reduction issue when TiO₂has been sintered in the air,which makes its microwave dielectric properties deteriorate sharply.In this thesis,TiO₂microwave ceramic materials were selected as the research ob-ject,and their microwave dielectric properties were improved by single ion doping（MoO₃,SnO₂）and compound ion doping（Cr₂O₃+Nb₂O₅,MnO+WO₃）.（1）In single ion doping,MoO₃ and SnO₂ doping were used to study the effects of these two ion doping on the crystal structure,microstructure and microwave dielectric properties of ceramics.There was no second phase due to its relatively small doping amount of MoO₃.However,MoO₃has a low melting point,and appropriate amount of MoO₃doping can promote the sintering process,and improve the quality factor of ce-ramics.SnO₂is completely solid solution with TiO₂,and Sn⁴⁺can inhibit the reduction of Ti⁴⁺to Ti³⁺,but excessive SnO₂doping will lead to the formation of a large number of pores inside the ceramic,which will deteriorate its performance.ε_rwas mainly af-fected by factors such as ion polarizability and density.Doping with MoO₃or SnO₂will decreaseτ_f.When x=0.005 and the sintering temperature was 1425℃,TiO₂-x MoO₃achieves optimal microwave dielectric properties ofε_r=107.8,Q×f=19,452 GHz,τ_f=508.8 ppm/℃.When x=0.16 and the sintering temperature is 1375℃,（1-x）TiO₂-x SnO₂achieves optimal microwave dielectric properties:ε_r=88.4,Q×f=20,777 GHz,τ_f=430.2ppm/℃.（2）In compound ion doping,the effects of Cr₂O₃ and Nb₂O₅co-doping and MnO and WO₃co-doping on the microwave dielectric properties of ceramics were studied.Cr₂O₃and Nb₂O₅will form Nb CrO₄during the sintering process.Nb CrO₄is a rutile TiO₂struc-ture and will form a solid solution with TiO₂.Similar to SnO₂doping,Cr₂O₃and Nb₂O₅co-doping will refine the ceramic grains.The Q×f of ceramics was affected by factors such as pores and Ti reduction.ε_rwas related to factors such as density and ion polariz-ability,andτ_fwas consistent with the change in dielectric constant.When x=0.06 and the sintering temperature was 1300℃,（1-x）TiO₂-0.25x Cr₂O₃-0.25x Nb₂O₅achieves optimal microwave dielectric properties:ε_r=103.4,Q×f=19,147 GHz,τ_f=459.4 ppm/℃.Due to the low doping amount of MnO and WO₃co-doping,the peak of the second phase can not be detected in the XRD,but the second phase was found in the SEM image.EDS results show that WO₃can only be partially dissolved in TiO₂.The appearance of the second phase can deteriorate the ceramic properties.Finally,when x=0.005 and the sin-tering temperature was 1425℃,（1-x）TiO₂-0.5x MnO-0.5x WO₃achieve better microwave dielectric properties:ε_r=104.0,Q×of=39,000 GHz,τ_f=464.4 ppm/℃.