Scalable Preparation of Fully Coated Ag@BaTiO₃ Core@Shell Particles via Poly(vinylpyrrolidone) Assistance for High-k Applications

This paper reports a poly(vinylpyrrolidone) (PVP)-assisted synthesis of Ag@BaTiO3 (BT) core@shell particles, consisting of smooth and fully coated BT shells on Ag cores. PVP adheres to Ag by coordination attraction, and it is present as a framework on the Ag surface. Driven by the adhesion forces from PVP, fully coated BT shells form on the template of the PVP framework. The shell phase is formed through a modified low-temperature direct synthesis method. Scanning electron microscopy examination of morphological evolution reveals smooth surfaces of the oxide coatings on Ag cores. X-ray diffraction pattern, energy-dispersive X-ray spectra, line scan, and mapping confirm the phase, chemical composition, and configuration of the shells. The synthesis method in this paper can achieve controllability of the growth rate and shell thickness. Because of the fully coated shells of BT, the poly(dimethylsiloxane) composites filled with synthesized core@shell fillers have very small leakage currents of ∼10–8–10–7 A/cm2. A high permittivity of 202 (εr/εm = 84) and a low dielectric loss of 0.003 are achieved at 1 MHz in composites filled with 40 vol % Ag@BT fillers. Lichtenecker’s theory containing the equivalent permittivity of core@shell Ag@BT originating from interfacial polarization is used to account for the dielectric constant of the composite. The smooth and fully coated Ag@BT core@shell particles can be used in composite materials for high-dielectric-constant and low-loss applications.