Improving Temperature-frequency Characteristics Of LaAlO₃-based Microwave Dielectric Ceramics

With the rapid development of 5G technology,microwave dielectric ceramic filters were widely used in 5G base stations due to their small size,high Q value,and high power capacity.However,high-performance ceramic dielectric filters are inseparable from high-performance Microwave dielectric ceramic materials.Therefore,the development of microwave dielectric materials with excellent performance becomes particularly important.In this paper,LaAlO₃-based microwave dielectric ceramics were used as the research object,La_1-xY_xAl O₃（x=0-0.2）and La[Al_1-x(Mg_0.5Ti_0.5)_x]O₃（x=0-0.2）series ceramics were prepared by traditional solid-phase method,and through XRD,TEM,SEM,Raman and other test methods,the phase composition,lattice structure,micro morphology and structure-effect relationship of the spectral characteristics and microwave dielectric properties of La Al O₃ ceramics with different ion substitutions were explored.The main conclusions were as follows:（1）When the La site of La_1-xY_xAl O₃ was replaced by Y³⁺,all the components had a stable rhombohedral structure,and the space group was R-3c.When x increases from 0 to0.1,the temperature coefficient of resonant frequency changed from-43.0ppm/℃ to-20.7ppm/℃.As x continues to increase,the temperature coefficient of resonant frequency deteriorated.The relative density and Q×f value both increased first and then decreased,reaching the best when x=0.05.The value ofτ_f decreased in the negative direction firstly,and the best value was at x=0.1,and then the value ofτ_f deteriorated.The value ofτ_f was affected by the bond energy.Increasing the bond energy will help improve the stability of La_1-xY_xAl O₃ ceramics and make the value ofτ_f near-zero.The best comprehensive microwave dielectric properties were:ε_r=22.44,Q×f=57910GHz,τ_f=-27.88ppm/℃.（2）When the Al site in La[Al_1-x(Mg_0.5Ti_0.5)_x]O₃ was replaced by the equivalent[Mg_0.5Ti_0.5]³⁺double ion,a solid solution was formed in the range of 0≤x≤0.2.The superlattice spots and the appearance of new vibration peaks at the 800cm^-1 wavenumber of the Raman spectrum indicated that the partial replacement of Al³⁺by[Mg_0.5Ti_0.5]³⁺ions can effectively improve the order of ion arrangement of LaAlO₃ ceramics,thereby increasing LAMT（x=0-0.2）Ceramic Q×f value.When x increased from 0 to 0.1,the temperature coefficient of resonant frequency changed from-43.0ppm/℃ to-33.0ppm/℃,and then the temperature coefficient of resonant frequency deteriorated.When x=0.1,the best microwave dielectric properties of the sample were:ε_r=24.9,Q×f=79956GHz,τ_f=-33ppm/℃.（3）By designing（1-x）La[Al_0.9(Mg_0.5Ti_0.5)_0.1]O₃-x Ca Ti O₃（x=0.2-0.8）series ceramics,the temperature coefficient of resonant frequency of the ceramic system was adjusted to be near-zero.Among them,the temperature coefficient of resonant frequency changed from negative to positive,and when x=0.65,τ_f was near-zero.When x=0.65,it had the best comprehensive microwave dielectric properties:ε_r=44.6,Q×f=32057GHz,τ_f=+2ppm/℃.