Enhanced microstructure and dielectric properties of low-temperature sintered MgO-xwt%LiF ceramics for high-frequency applications

Abstract

MgO ceramics show good microwave dielectric properties, but their high sintering temperature limits the practical applications. LiF is an ideal sintering aid (melting point of 848 °C) and does not easily react with MgO to form any secondary phase. Herein, MgO- x wt%LiF ceramics ( x = 2–10, with a step of 2) with ultralow loss were fabricated using a conventional solid-state process. The X-ray diffraction and Rietveld refinement results revealed that the lattice parameters and unit cell volume of the ceramics first increased and then decreased with LiF content increase. The compositions of the ceramics were analyzed using energy-dispersive X-ray spectroscopy, and superfluous LiF appeared when x ≥ 4. Notably, at x = 4 and T = 950 °C, the grain distribution was dense and uniform, and the quality factor of the MgO- x wt%LiF ceramics reached the maximum value of 120288 GHz (at 12 GHz), and the other properties also attained the optimal level: ε r = 9.66 and τ f = -20.66 ppm/°C. Meanwhile, the dielectric properties of the ceramics were studied over a broad frequency range (up to the terahertz frequencies). The ceramics showed excellent dielectric properties, such as a low dielectric constant of 9.252 (at 1 THz) and a low dissipation factor tanδ of 0.0058. In summary, the MgO ceramics were not only found to be suitable for application in the microwave range, but also showed huge potential for application value in the terahertz frequency range.