Improvement of Microwave Dielectric Properties by Impact of Sodium Ion Doping in Complex Oxides for Polymer Composites

Abstract

The research presented in this study focuses on the dielectric properties of complex oxide-filled epoxy, polyurethane, and silicone rubber composites. Specifically, we investigated various compositions of (1-x) CaWO₄-xNa₂WO₄ (x = 0, 0.2, 0.4), in addition to Na_0.5Bi_0.5Mo_0.5W_0.5O₄ and Bi₂Mo_0.5W_0.5O₆. These complex oxide materials were meticulously synthesized through a solid-state reaction, and their distinct phases were confirmed via rigorous X-ray diffraction (XRD) characterization. We then proceeded to create the composites by manually blending these complex oxides with epoxy, polyurethane, and silicone rubber matrices. The central focus of the study was to examine the impact of varying volume fractions of the complex oxide fillers on the dielectric properties of the composites in the frequency range of 4 – 8 GHz.Our observations revealed a direct correlation between the content of the complex oxide filler and the dielectric properties, including the dielectric constant and dielectric loss. Specifically, the addition of 10 % by volume fraction of (1-x) CaWO₄-xNa₂WO₄ (x = 0, 0.4), Na_0.5Bi_0.5Mo_0.5W_0.5O₄, or Bi₂Mo_0.5W_0.5O₆ fillers to the respective polymer matrices led to a significant enhancement in both the dielectric constant and the loss tangent. Promising results were particularly evident in three composite formulations: the 10 % 0.4Na₂WO₄-0.6CaWO₄/silicone rubber composite demonstrated a dielectric constant (ε_r) of 2.02 ´ 10² and a loss tangent (tanδ) of -4.07 ´ 10^-1 at 7.1 GHz; the 10 % Na_0.5Bi_0.5Mo_0.5W_0.5O₄/epoxy composite exhibited a dielectric constant of 1.37 ´ 10² and a loss tangent of -6.43 ´ 10^-1 at 7.22 GHz; and the 10 % Bi₂W_0.5Mo_0.5O₆/polyurethane composite displayed favorable properties with a dielectric constant (ϵr) of 8.37x10¹ and a loss tangent (tanδ) of -3.4 ´ 10^-1 at 7.12 GHz.These results suggest the suitability of these composite materials for a wide range of microwave technology applications, including wireless communication, radar systems, and various microwave devices.