Preparation of BaTiO3/low melting glass core–shell nanoparticles for energy storage capacitor applications

Abstract

A core–shell nano-scale mixing technique was applied to fabricate BaTiO₃/glass nanocomposites in order to preserve the nano-grain dielectric properties of BaTiO₃ after sintering and enhance the bulk composite energy storage capability. Coating layers of low melting glasses of lead borosilicate glass (65PbO–20B₂O₃–15SiO₂, mol%) and bismuth borosilicate glass (65Bi₂O₃–20B₂O₃–15SiO₂, mol%) were deposited onto BaTiO₃ nanoparticles in chemical solution by a sol-precipitation method under ultrasonic agitation. Transmission electron microscopy (TEM) results confirmed the formation of core–shell nanostructures with controllable shell thicknesses between 2 and 18 nm. X-ray diffraction (XRD) patterns showed that no crystalline peaks were detected from the glass coating layer. Fourier transform infrared (FT-IR) spectra indicated a glass network structure of lead borosilicate glass and bismuth borosilicate glass, respectively. High densifications were achieved for both composites by sintering at low temperatures (≤900 °C). Noticeable grain growth was observed for the lead borosilicate glass-coated BaTiO₃ (Pb-BT) composite while almost no grain growth was observed for the bismuth borosilicate glass-coated BaTiO₃ (Bi-BT) nanocomposite. This disparity was attributed to the different interactions between the BaTiO₃ core and two glasses during the sintering process, as revealed by the XRD study. Dielectric properties and energy storage capability of the Bi-BT nanocomposite were investigated in detail. The Bi-BT nanocomposite showed high polarization, high dielectric breakdown strength (≥1000 kV cm⁻¹), postponed polarization saturation, and low remnant polarization with the discharge energy density of ∼10 J cm⁻³ at 1000 kV cm⁻¹. Thus, the Bi-BT core–shell nanocomposite appears to be a promising material system for energy storage capacitor applications.