Modification Of ZnTiNb₂O₈-based Microwave Dielectric Ceramics By Ions Substitution

With the rapid development of 5G communications,microwave components such as microwave filters and microwave resonators had become increasingly demanding for microwave dielectric properties of middle-dielectric constant ceramics.The middle-dielectric constant ceramics of ZnTiNb₂O₈ systems had attracted much attention.However,the ZnTiNb₂O₈ system has always had the problem of poor temperature coefficient of resonant frequency,which was not conducive to practical applications.For this problem,the main work and results of this thesis were as follows:Firstly,the effect of Co²⁺substitution of Zn²⁺on microwave dielectric properties of ZnTiNb₂O₈ ceramics were studied.By adjusting the content of Co²⁺and sintering temperature,the best point of microwave dielectric properties of(Zn_1-xCo_x)TiNb₂O₈?x=0,0.1,0.2,0.3,0.4,0.5?ceramics were determined.Due to the appearance of the second phase Co_0.5Ti_0.5NbO₄ at x?0.3,the dielectric constant increased,the Q×f value decreased sharply,and the temperature coefficient of resonant frequency approached zero.Finally,the microwave dielectric ceramics with?_r=39.0,Q×f=6968 GHz,and?_f=+2.2 ppm/°C at the sintering temperature of 1150°C and x=0.4 were obtained which had the relatively poor dielectric loss.Secondly,the effect of(Al_1/2Nb_1/2)⁴⁺substitution of Ti⁴⁺on microwave dielectric properties of ZnTiNb₂O₈ ceramics were studied.By adjusting the content of(Al_1/2Nb_1/2)⁴⁺and sintering temperature,the best point of microwave dielectric properties of ZnTi_1-x(Al_1/2Nb_1/2)_xNb₂O₈?x=0,0.2,0.4,0.5,0.6?ceramics were determined.With the increase of(Al_1/2Nb_1/2)⁴⁺content?x<0.6?,the ion polarizability decreased,which resulted the dielectric constant decreased;the degree of ion ordering increased,which resulted Q×f value increased;the decrease of the value of the bond valence,which resulted the temperature coefficient of resonant frequency changed to the positive direction.With the(Al_1/2Nb_1/2)⁴⁺content further increased?x?0.6?,the second phase AlNbO₄ was dectected that resulted in the Q×f value and the temperature coefficient of resonant frequency decreased.Finally,the microwave dielectric ceramics with?_r=27.4,Q×f=65400GHz and?_f=-56.2ppm/°C at the sintering temperature of 1175°C and x=0.5 were obtained which had the relatively poor temperature coefficient of resonant frequency.Finally,the effect of Co²⁺substitution of Zn²⁺on microwave dielectric properties of ZnTi_0.5(Al_1/2Nb_1/2)_0.5Nb₂O₈ ceramics were studied.By adjusting the content of Co²⁺and sintering temperature,the best point of microwave dielectric properties of(Zn_1-xCo_x)Ti_0.5(Al_1/2Nb_1/2)_0.5Nb₂O₈?x=0,0.2,0.4,0.5,0.55,0.6?ceramics were determined.Due to the appearance of the second phase Co_0.5Ti_0.25(Al_1/2Nb_1/2)_0.25NbO₄,the dielectric constant increased,the Q×f value decreased,and the temperature coefficient of resonant frequency approached zero.Finally,the microwave dielectric ceramics with?_r=31.1,Q×f=39200GHz,?_f=-8.9 ppm/°C at the sintering temperature of 1150°C and x=0.55 were obtained which met the desired goal.