Preparation And Performances Of Novel AB₂O₄-Type Low Permittivity Microwave Dielectric Ceramics

Microwave dielectric ceramics（MWDC）are one of the key materials in microwave circuits.In order to achieve good signal transmission quality and respond to the development trend of high frequency technology,the development of microwave dielectric ceramic materials with low dielectric constant,high Q×f value and near-zeroτ_f is an urgent problem to be solved.In this paper,novel series of AB₂O₄ type microwave dielectric ceramics were systically investigated,such as Sr Y₂O₄,Ca Y₂O₄,Sr Sm₂O₄,Ba Sm₂O_4.The microwave dielectric properties of Sr Y₂O₄ ceramic were optimized.Furthermore,microwave dielectric resonator antennas for 5G band were designed and prepared using this material.（1）Sr Y₂O₄（SY）ceramics of low dielectric AB₂O₄ type were prepared by the solid state reaction method.The SY ceramics exhibited pure Sr Y₂O₄ phase in the sintering temperature range.The average grain size of the samples increased with rising the sintering temperature.However,the relative density and dielectric constant showed a tendency to increase firstly and then decrease.Good microwave dielectric properties were obtained for the SY ceramics sintered at 1475°C for 4 h:ε_r=14.78,Q×f=84090GHz,τ_f=-14.98 ppm/°C.（2）To optimize the microwave dielectric properties of the SY ceramics,nonstoichiometric Sr_1+xY₂O_4+x（x=0～0.4）ceramics were prepared by the solid state reaction method.All diffraction peaks of Sr_1+xY₂O_4+x（x=0～0.4）ceramics were matched well with the standard card of Sr Y₂O₄.When x=0.2,the ceramics have excellent microwave dielectric properties:ε_r=15.41,Q×f=112375 GHz,τ_?=-17.44 ppm/°C.Subsequently,2 wt%of Ca Ti O₃ was added to adjust theτ_?value of the ceramic to 0,while the ceramic had good microwave dielectric properties:ε_r=16.14,Q×f=51004GHz,τ_?=0 ppm/°C.Dielectric resonator antennas were prepared using this ceramic:center frequency,gain and efficiency were 26.6 GHz,3.66 d Bi and 83.14%,respectively.（3）Ca Y₂O₄（CY）ceramics consisting of two phases,Ca O and Y₂O₃,were prepared by the reaction sintering method.The results showed that all diffraction peaks of this ceramic are matched well with those of Y₂O₃ and Ca O.The ceramics sintered at 1400°C have good microwave dielectric properties ofε_r=4.30,Q×f=33360 GHz,τ_?=-13.79ppm/°C.（4）The low dielectric AB₂O₄-type Sr Sm₂O₄（SS）ceramics were prepared by the solid state reaction method.The SS ceramics were composed of Sr Sm₂O₄ single phase.Good microwave dielectric properties were obtained for ceramic sintered at 1400°C:ε_r=18.16,Q×f=40646 GHz,τ_f=-17.6 ppm/°C.（5）Ba Sm₂O₄（BS）ceramics of low dielectric AB₂O₄ type were prepared by the solid state reaction method.All diffraction peaks of the ceramics are matched well with Ba Sm₂O₄ standard cards.XPS results showed that part of Sm³⁺was reduced to Sm²⁺at high temperature.The dielectric constants,Q×f andτ_f of the ceramics are closely related to the relative density,stacking fraction and oxygen octahedral distortion,respectively.It was finally found that the BS ceramics sintered at 1500°C had good microwave dielectric properties withε_r=10.99,Q×f=54598 GHz,andτ_f=-25.4 ppm/°C.