Study Of Microwave Dielectric Properties Of LaNbO₄ Ceramic System

The research of ceramic materials will focus on multi-functional materials in order to promote high-tech theoretical and practical industrial restructuring.In this area,Chinese technology investment is relatively backward,and many advanced technologies still need to be imported from western countries.Therefore,we need to devote more energy to studying new multifunctional materials.Microwave dielectric ceramic material is one kind basic multi-functional material,which is widely used in mobile communications,biomedical and public infrastructure.In this paper,the lanthanum niobate dielectric ceramics is a kind of rare earth niobate ceramic system with many functions.We focus on the structure and microwave dielectric properties of the ceramics.Our study start from the following aspects:1.Pure phase LaNbO4 ceramics were prepared and the crystal structure of them were analyzed.The results showed that LaNbO4 ceramics belong to monoclinic system.Based on the complex chemical bond theory,the properties of various chemical parameters of LaNbO4 ceramics were calculated theoretically.The chemical bond parameters?Dielectric constant,quality factor,temperature coefficient?and the microwave dielectric properties?dielectric constant,quality factor and temperature coefficient of resonant frequency?were analyzed.The relationships between the change of crystal structure caused by sintering temperature and the microwave dielectric properties of pure phase ceramics were analyzed.2.The effects of Sm³⁺ion substitution on the structure and properties of(La_1-xSmx)NbO4 ceramics were studied systematically.The crystal structure,chemical bond properties and microwave dielectric properties of the samples were studied emphatically.The influence of Nb⁵⁺ion replaced by Ta⁵⁺ion on the chemical bond properties and structure of LaNbO4 ceramics were also studied.3.BaCu?B2O5?additive was added to the lanthanum niobate ceramic powder.The optimum sintering temperature of LaNbO4 could be reduced from 1325^oC to 925 ^oC with 1wt%BaCu?B2O5?doping.Since BaCu?B2O5?has a large temperature coefficient of 75ppm/^oC,the temperature coefficient of resonant frequency of samples with BaCu?B2O5?became bigger and bigger.All in all,pure phase lanthanum niobate ceramic was firstly prepared,then do in-depth study from the two points according to its unique structure,they are glass doping and ion substitution.Finally,do structure refinement by Rietveld to explore the effect of ion substitution on ceramic crystal structure,and calculate the chemical bond parameters which can measure the structure characterization.The purpose for all of this is to study systematically the change trend of microwave dielectric performance from the angle of intrinsic reason.