Medium dielectric constant and low-loss PTFE composites filled with MgO-LiF co-doped Li₂TiO₃ particles

In this work, we presented a simple strategy to fabricate medium dielectric constant and low-loss composites for microwave substrate applications. MgO-LiF co-doped Li₂TiO₃ (LT) powders were fabricated by the solid-state reaction route and modified by perfluorooctyltriethoxysilane (F8261). The LT/polytetrafluoroethylene (PTFE) composites were fabricated by cold pressing and hot treatment. The XPS and contact angle analysis indicated that the fluorinated group was introduced to LT particle successfully. The effects of modified LT powders content on the dielectric, thermal, and mechanical properties of composites were investigated. As the modified LT content increases, the dielectric constant, dielectric loss, and temperature coefficient of dielectric constant (τ_ε) increase while the bending strength and coefficient of thermal expansion (CTE) decrease, which is attributed to the higher dielectric constant of LT ceramic, more pores, stable τ_ε of LT ceramic, interface defects and low CTE of LT ceramic, respectively. The composites with 60 wt % LT exhibit the best microwave dielectric properties: ε_r = 6.8, tanδ = 0.001, τ_ε = −29.6 ppm °C⁻¹ at 8 GHz and acceptable coefficient of thermal expansion (28.3 ppm °C⁻¹). Therefore, modified LT powders filled PTFE composites are potential materials for high-frequency microwave substrate applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47980.