Study On La-Ni-Ti Based Microwave Dielectric Ceramic Materials

With the rapid development of microwave technology in the field of mobile communications,the demand for higher dielectric constant,high quality and high temperature stability microwave dielectric materials ismore and more urgent.The0.97La_2/3TiO₃-0.03NiTiO₃ ceramic material has become a promising material because of its high dielectric constant,high quality factor,and adjustable temperature coefficient of the resonant frequency.This dissertationstartedfrom the aspects of base material preparation,technological research,non-stoichiometry,doping modification,etc.of La-Ni-Ti based microwave dielectric ceramics,studying the La-Ni-Ti based microwave dielectric ceramic materials Systematically.Firstly,the ceramic system was studied from the basic formulation and process.Based on the La₂O₃-TiO₂ ceramic system as the basic formulation,the effect of Ni's addition and addition amount on the formation of La_2/3TiO₃ phase was first investigated.It was found that the addition of Ni is very important for the generation of La_2/3TiO₃ phase.When 3 wt%of NiO was added,a La_2/3TiO₃ phase which was of little impurity phase can be produced.In addition,the pre-firing process and synthesis process of the 0.97La_2/3TiO₃-0.03NiTiO₃ ceramic system were also studied.It was found that the pre-sintering temperature is 1150°C,and the 0.97La_2/3TiO₃-0.03NiTiO₃ceramic material prepared by the one-step synthesis process is superior.Secondly,The influence of non-stoichiometric ratio on microwave dielectric properties and microstructure of 0.97La_2/3TiO₃-0.03NiTiO₃ ceramic system was investigated.It is found that the appropriate non-stoichiometric ratio of La ions and Ni ions can improve the microwave dielectric properties of the system,inhibit the generation of heterophasic phase,and increase the structural density of the ceramic system.Finally,the effect of doping on the microstructure and microwave dielectric properties of 0.97La_2/3TiO₃-0.03NiTiO₃ ceramics was studied.Doping includes doping of rare earth elements and ion doping of A and B sites.Rare earth element doping includes Sm₂O₃ doping and Ho₂O₃ doping.The results showed that proper amount of Sm doping could effectively increase the sintered density of ceramic system and reduce the resonant frequency coefficient of the system.However,as the amount of doping increases,the second phase also begins to increase,resulting in a decrease in microwave dielectric properties.The incorporation of Ho improved the sintering density of the ceramic system,and effectively improves the frequency-temperature stability when the dielectric constant and quality factor were reduced.The ion doping of A and B sites includes Li₂CO₃ doping of A site and ZrO₂ doping of B site.The results showed that the appropriate amount of Li doping could effectively improve the sintering density of the ceramic system.The doping of the ceramic system could effectively reduce the resonant frequency temperature coefficient of the ceramic system and increased the dielectric constant,but the deterioration of the quality factor was obvious.The incorporation of Zr improved the sintered density of the ceramic system,but there was no significant change in the dielectric properties and microstructure,and the resonant frequency temperature coefficient increased.In the system research carried out in this topic,the system with better microwave dielectric properties is listed as follows:?1?0.97La_2/3TiO₃-0.03NiTiO₃:?_r=67.71,Q×f=15765 GHz,?_f=125 ppm/oC.?2?0.97La_2?1-x?/3Sm_2x/3TiO₃-0.03NiTiO₃?x=0.1?:?_r=55.2,Q×f=9399GHz,?_f=89ppm/oC.?3?0.97La_2?1-x?/3Ho_2x/3TiO₃-0.03NiTiO₃?x=0.1?:?_r=67.42,Q×f=11755GHz,?_f=96ppm/^?.