Research On Dielectric Properties Of LaAlO₃-SrTiO₃ And NdAlO₃-CaTiO₃

MTiO₃-LnAlO₃?M=Sr?Ca,Ln=Nd?La?has many advantages,such as low loss,high dielectric constant and good microwave performance,which is widely used in microwave devices.In order to prepare low loss dielectric material with low dielectric constant of about35,this thesis focuses on the study of this material,La_xAlO₃-SrTiO₃,xLaAlO₃-?1-x?SrTiO₃and NdAlO₃-CaTiO₃ ceramics are prepared with the conventional solid-state reaction,the microstructure and dielectric properties of the samples are studied:The influence of the molar ratio of La to Al on the La_xAlO₃-SrTiO₃?x=0.6-1.0?is studied.In the 0.675La_xAlO₃-0.325SrTiO₃,the x?0.9 sample forms solid solution,when the x=0.6 sample does not generate heterogeneous phase.The microwave dielectric constant of the x=0.6 sample is 30,and the Q×f value is 21656GHz.In the 0.6La_xAlO₃-0.4SrTiO₃,when the sintering temperature is 1550^?,the increase of x from 0.575 to 0.9,the dielectric constant of the samples decrease from 41.93 to 37.08,the loss tangent increases from 0.0214to 0.0135.The microwave dielectric constant of the x=0.8 sample is 32.7,and the Q×f value is 31684GHz.The effect of SrTiO₃ on xLa_0.6AlO₃-?1-x?SrTiO₃ is studied,the x=0.5?0.55and 0.6 samples form solid solution generates,the x=0.65 sample generates La₂O₃heterogeneous phase.When the sintering temperature is 1550^?,the increase of x from 0.6to 0.65,the dielectric constant of the samples decrease from 48.2 to 37.7,the loss tangent decreases from 0.00416 to 0.0014.The microwave dielectric constant of the x=0.6 and 0.65samples are 34 and 31,respectively.And the Q×f value of the x=0.6 and 0.65 samples are17062 GHz and 19440GHz.Thick pellet with x=0.5 and 0.55 becomes blue,because Ti⁴⁺is reduced to Ti³⁺at high temperature;0.55La_0.6AlO₃-0.45SrTiO₃ with a small amount of MnCO₃ addtions to inhibit reduction of Ti⁴⁺.Although the addition of MnCO₃ does not have effect on the microwave dielectric constant,the Q×f value decreases from 24904GHz to20020GHz.The effect of LaAlO₃ content on xLaAlO₃-?1-x?SrTiO₃ is studied.Under the condition of the calcination temperature is 1300^?,when the sintering temperature is 1500^?,the samples can not form a solid solution,when the sintering temperature is 1600^?,x=0.5?0.55and 0.6 can form a solid solution,the microwave dielectric constant of the x=0.6 sample is28.76,the Q×f value is 38184GHz.Under the condition of the calcination temperature is increased to 1400^?,when the sintering temperature of 1500^?,the x=0.65 sample does not form solid solution,when the sintering temperature of 1550^?,the decrease of SrTiO₃content from 50%to 40%,the dielectric constant of the samples decrease from 45.3 to 39.7.The microwave dielectric constant of the 0.5LaAlO₃-0.5SrTiO₃ sample is 36.15,and the Q×f value is 37933GHz.Doping with a small amount of Nb₂O₅ can reduce the sintering temperature to make 0.65LaAlO₃-0.35SrTiO₃ form solid solution.When doping with Nb₂O₅content is 2%,the microwave dielectric constant of the sample is 29.95,and the Q×f value is 16633GHz.The influence of the molar ratio of Nd to Al and CaTiO₃ content on NdAlO₃-CaTiO₃ is studied.When the sintering temperature is 1500^?,the decrease of x from 0.9 to 0.6,the dielectric constant of the samples increase from 37.7 to 40.5,the microwave dielectric constant of the samples increase from 30.17 to 33.11,the Q×f value decreases from19134GHz to 3163GHz;When the sintering temperature is 1525^?,the decrease of CaTiO₃content from 50%to 35%,the dielectric constant of the xNdAlO₃-?1-x?CaTiO₃ samples decrease from 39.9 to 33.7,the microwave dielectric constant of the x=0.5 sample is 32,and the Q×f value is 24541GHz.