Sintering Behavior, Crystal Structure, and Microwave Dielectric Properties of Li2Y9(SiO4)6O2F Ceramics with Near-Zero τf

This study delves into the microwave dielectric properties of Li₂Y₉(SiO₄)₆O₂F ceramics, synthesized using the conventional solid-state method. By employing x-ray diffraction analysis and meticulous data refinement across various temperatures, we unequivocally confirm the hexagonal crystal structure of Li₂Y₉(SiO₄)₆O₂F ceramics. The refined lattice parameters, observed at a sintering temperature of 1275°C, exhibit a = b = 9.33318 Å, c = 6.71725 Å, with a corresponding unit cell volume of V = 506.73529 ų. In-depth scrutiny of the microstructure of the ceramics’ grains using scanning electron microscopy (SEM) reveals an optimal relative density of 96.2%. Subsequently, the study explores the impact of porosity, packing fraction, relative density, and Si-O bond valence (V_Si-O) on the microwave dielectric properties of Li₂Y₉(SiO₄)₆O₂F ceramics. Notably, the Li₂Y₉(SiO₄)₆O₂F ceramic sintered at 1275°C demonstrates superior performance metrics, boasting an ε_r value of 14.28, a Q × f product of 16,760 GHz (at f = 9.4 GHz), and a temperature coefficient of frequency (τ_f) at 3.14 ppm/°C. This comprehensive investigation contributes valuable insights into optimizing the microwave dielectric characteristics of Li₂Y₉(SiO₄)₆O₂F ceramics for potential applications in advanced electronic devices.