Synthesis and characterization of PTFE/(NaxLi1-x)0.5Nd0.5TiO3 composites with high dielectric constant and high temperature stability for microwave substrate applications

Abstract

In the current work, (NaxLi1-x)0.5Nd0.5TiO3 (abbreviated to NLNT100x, x = 0.3,0.4,0.5,0.6,0.7) ceramics were synthesized by solid phase reaction. X-ray diffraction analysis confirmed the successful synthesis of NLNT ceramics. Dielectric measurements of the synthesized ceramics show that the dielectric constant (εr) is increased first as increasing x, then decreased at x > 0.5, meanwhile the temperature coefficient of dielectric constant (τε) varied toward negative direction with the increase of x. Then, composite substrates with high dielectric constants and adjustable τε were fabricated by filling polytetrafluoroethylene (PTFE) with 60 wt% NLNT100x ceramics and using 5 wt% E glass fibers (E-GF) as reinforcement materials. In order to improve the interfacial compatibility of ceramics with PTFE polymer, hydrogen peroxide (H2O2) was used to enhance the hydroxyl group (-OH) on the surface of inert perovskite ceramics, which is conducive for ceramics to further react with silane coupling agent (F8261 in this work). The modified ceramic was homogeneously dispersed in PTFE and composites with excellent dielectric properties were obtained. When x is 0.6, the prepared NLNT/PTFE composite substrate has a dielectric constant (εr) of 10.4, a low dielectric loss (tan δ) of 0.0026, and a near-zero dielectric constant temperature coefficient (τε) of approximately −-0.9 ppm/°C.