Process And Modification Of CaSmAlO₄-Based Microwave Dielectric Ceramics

5G technology,as the mainstream means of mobile communication today,provides a strong and powerful aid to the recovery of the main social economy,the resumption of work and work from home.As the proportion of devices prepared from microwave dielectric materials in communication equipment is increasing,the attention paid to microwave dielectric materials with high performance and low loss is also increasing.In this paper,CaSmAlO₄-based ceramics with K₂Ni F₄ structure were selected as the object of study,and the mechanism of hydration and the evolution of the physical phase structure of the ceramic materials appeared during the solid-phase preparation process were investigated in detail.At the same time,the correlation between the physical phase structure,microscopic morphology and dielectric properties of CaSmAlO₄-based ceramics was further explored through the doping of different ions by the solid-phase method.In this paper,Ca_1.15Sm_0.85Al_0.85Ti_0.15O₄ ceramics were first synthesized in one step by a conventional solid phase method.By analyzing the XRD spectra of the powders prepared at different slurry temperatures,it was found that a higher ball milling temperature（45±5°C）leads to the hydration of the material phase and the formation of a large amount of（Ca O）₃Al₂O₃（H₂O）₆ phase at the same time.Scanning electron microscopy and energy spectroscopy results confirm that the hydration leads to a non-uniform grain size distribution on the ceramic surface,which causes deterioration of the dielectric properties of the samples.The hydration was significantly suppressed when the slurry temperature was controlled in the 20±5°C range.At this point,the ceramics sintered at 1450°C exhibited excellent microwave dielectric properties withε_r=19.22,Q×f=70034 GHz,τ_f=-1.25 ppm/°C.On this basis,the effects of different sites of Sm/Mg and Mg/Ti doping on the microwave dielectric properties of CaSmAlO₄-based ceramics were investigated by analyzing the degree of densification,crystal structure,and microscopic morphology characterization results.The results of refinement revealed that Sm/Mg co-doping led to different degrees of increase in cell parameters and cell volume of the ceramics.At doping levels below 0.2,the ceramics are single-phase,and excessive doping causes the appearance of heterogeneous phases to deteriorate the dielectric properties.At x=0.2,relatively good dielectric properties were obtained at 1475°C for 4 h:ε_r=21.12,Q×f=50688 GHz,τ_f=-0.5 ppm/°C.The Mg/Ti co-doping resulted in partial replacement of Al³⁺at the B-site by the complex ion(Mg_0.5Ti_0.5)³⁺.Analysis of the ceramic surface grain size revealed that the doping ions have a good contribution to the growth of the ceramic grains.Raman spectroscopy results show that Mg/Ti doping causes Ca/Sm-O_（2a）-Ca/Sm ionic bond stretching and Ca/Sm-O_（2b）ionic bond compression.These changes together lead to an optimization of the dielectric properties of the ceramics.the best dielectric properties are obtained for Ca Sm Al_1-x(Mg_0.5Ti_0.5)_xO₄（0.1≤x≤0.4）ceramics for Mg/Ti doping of 0.2:ε_r=20.24,Q×f=63367 GHz,τ_f=0.67 ppm/°C.