With the development of microwave communication technology,as one of the key materials in the field of microwave communication,microwave dielectric ceramics have good performance and application prospects.The downstream application of microwave dielectric ceramics like mobile communications,satellite communications,military radar,electronics industry,global satellite positioning system(GPS),Bluetooth technology,other defense military industry and many other industries are booming,the technical level is constantly upgrading,the need for better performance of microwave dielectric ceramics to meet the application requirements.Ba(Mg1/3Nb2/3)O3(BMN)ceramics and Ln Al O3(Ln=La,Nd,Sm)ceramics have moderate dielectric constant and high quality factor,but their resonant frequency temperature coefficientτf is relatively high.In view of the fact that the two have opposite resonant frequency temperature coefficients,this paper attempts to compound Ba(Mg1/3Nb2/3)O3 with Ln Al O3 in order to obtain a new microwave dielectric ceramic material with excellent performance.In this paper,Ba(Mg1/3Nb2/3)O3-Ln Al O3 ceramics were prepared by traditional solid state reaction method.The microstructure of Ba(Mg1/3Nb2/3)O3-Ln Al O3 samples was analyzed by scanning electron microscope(SEM)and X-ray energy dispersive spectrometer(EDS),and the grain morphology,element distribution and chemical composition were obtained.The phase structure of microwave dielectric ceramics was analyzed by XRD and Raman spectroscopy,and the full spectrum of diffraction data was fitted by Rietveld method in the Full Prof Suite program,so as to obtain the cell size and lattice parameters.The dielectric properties of Ba(Mg1/3Nb2/3)O3-Ln Al O3 samples were tested in microwave frequency band,and the effects of composition and structure on dielectric properties were analyzed.The intrinsic dielectric loss of the ceramic samples was analyzed through far-infrared spectroscopy.The main research results of this paper are as follows:The(1-x)Ba(Mg1/3Nb2/3)O3-x La Al O3 ceramics was well sintered at 1450℃.The main crystalline phase structure of the ceramics varied greatly with the composition.With the increase of x value,the main crystalline phase changed from 1:2 order to 1:1 order,and then to1:1 order structure and cubic disorder structure coexist.At x=0.1,the sintering body was dense,the order degree of B-site ions was relatively high,and the optimum dielectric properties withεr=33,Q×f=25 178 GH andτf=51.29 ppm/℃were obtained.The(1-x)Ba(Mg1/3Nb2/3)O3-x Nd Al O3 ceramics were well sintered at 1450℃.As the x value increased,the ceramic samples of which also underwent a series of structural phase transitions:1:2 ordered hexagonal perovskite→disordered cubic perovskite→low-symmetry structure perovskite.The(1-x)Ba(Mg1/3Nb2/3)O3-x Sm Al O3 ceramics was well sintered 1475℃,the structural phase transition of which was basically consistent with that of(1-x)Ba(Mg1/3Nb2/3)O3-x Nd Al O3.The dielectric constantεrof Ba(Mg1/3Nb2/3)O3-Ln Al O3 ceramics was greater than those of the terminal components of Ba(Mg1/3Nb2/3)O3 and Ln Al O3.By the far infrared analysis,it was found that the calculated value of the dielectric constant in the microwave frequency band was in good agreement with the measured value,the optical frequency dielectric constant accounted for less than 5%of the dielectric constant in the microwave frequency band,which proved that the main polarization contribution of dielectric constant came from the ion polarization.In addition,the imaginary partε′′calc of the extrapolation theory is in the same order of magnitude as the imaginary partε′′obs measured by the closed-cavity method,indicating that the dielectric loss of the ceramic material is mainly from the infrared phonon near the microwave.The frequency and temperature coefficientτf of Ba(Mg1/3Nb2/3)O3-Ln Al O3 with ordered structure were positive and greater than that of the terminal component of Ba(Mg1/3Nb2/3)O3.The nearly zeroτf value was not obtained by the composite of Ba(Mg1/3Nb2/3)O3 and Ln Al O3 with oppositeτf ones. |