Lattice Vibration Characteristics and Dielectric Response Mechanisms in Low-Temperature Sintered SrSn(BO3)2 -x wt.% LiF Microwave Ceramics for 5G Microstrip Antenna Applications

Abstract

In this study, SrSn(BO 3 ) 2 -x wt.% LiF microwave ceramics were successfully prepared at a sintering temperature of 950 °C using a traditional solid phase sintering method. The crystalline phases and morphologies of these samples were examined using an X-ray diffractometer (XRD) and scanning electron microscope (SEM), respectively. XRD shows no secondary phase detected. SEM images prove that the sample at x = 3.0 wt% has the the most uniform particle size with the highest density. The lattice vibrational characteristics were investigated using Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR) techniques.With the increase of the LiF content, when the A g mode moves to higher wavenumber, the B-O bond length decreases leading to a lower polarizability, so the dielectric constant decreases. The FWHM of the v 2 mode is closely related to the ordered degree, which is negatively correlated with the Q × f value. Seven vibrational modes were observed in the FTIR spectra, and the intrinsic dielectric properties were fitted and simulated according to the four-parameter semiquantum model, and thus the dielectric response mechanisms were interpreted based on the lattice dynamics. And accordingly, each vibrational mode and its respective contribution to the dielectric response was obtained. Among them, mode 2 contributes the most to the dielectric constant (33.33%), and contributes the most to the dielectric loss (53.84%). Results indicate that SrSn(BO 3 ) 2 -3 wt.% LiF ceramics exhibit outstanding microwave dielectric properties: ε r = 5.17, Q × f = 42,211 GHz (f = 15.72 GHz), τ f = -42.31 ppm/°C. Microstrip patch antenna was simulated utilizing this SrSn(BO₃)₂ -3 wt.% LiF ceramics as a dielectric substrate by HFSS software.The centre fre quency of this antenna was determined to be 12.0 GHz, which exhibited a return loss (S 11 ) of -40.0 dB and a peak gain of 6.86 dBi.