Dielectric response mechanism and structure–property relationships of SrSn(BO3)2 microwave ceramics with ultra-low permittivity and their application for 5G microstrip patch antenna

In this work, strontium tin borate [SrSn(BO₃)₂, SSBO] microwave dielectric ceramics (MWDCs) were synthesized using the traditional solid-state sintering method at different sintering temperatures. The formation of phase-pure SSBO ceramics was determined by the Rietveld refinement of X-ray diffraction patterns, and the sample sintered at 1150 °C showed the densest micro-morphology. Lattice vibrational spectroscopy was used to interpret the intrinsic properties to develop structure-property relationships of the SSBO MWDCs. Seven distinct Raman-active vibrational modes were observed in the Raman spectra, and nine distinct vibrational modes were identified in the infrared spectra. The intrinsic dielectric properties were fitted and simulated by the four-parameter semi-quantum model according to the far-infrared reflection spectra of the ceramics. The dielectric responses of the SSBO ceramics were revealed based on their Raman and infrared spectra, and the microstructural origins of the dielectric responses were also clarified. Therefore, the correlations between the crystal structures and the dielectric properties of the SSBO ceramics were created from the Raman phonon modes. The B-O bond lengths and the A_g mode shifts were closely related to the dielectric constants. The full-widths at half maximum of the v₂ modes were positively correlated with the quality factor values. The SSBO ceramic sintered at 1150 °C exhibited the best dielectric properties of ε_r = 5.42, Q × f = 32,618 GHz (f = 15.68 GHz), and τ_f = - 48.28 ppm/°C. This indicates that this sample was an ultra-low-permittivity MWDC with great potential for 5G applications. Simulation of this SSBO sample as a dielectric substrate was conducted using HFSS to fabricate a microstrip patch antenna capable of operating at 5.17 GHz, which exhibited a return loss (S11) of - 23.4 dB and a gain of 6.58 dBi.