Flexible Nanocomposites Comprised of Poly(dimethylsiloxane) and High-Permittivity TiO₂ Nanoparticles Doped with La³⁺/Cu⁺ for Dielectric Applications

Highly ordered spherical titania (TiO2) and La3+/Cu+-doped TiO2 nanoparticles with particle sizes of ≤∼20 nm are prepared by the sol–gel method using titanium isopropoxide [Ti(O-iPr)4] as the main raw material. The prepared nanoparticles are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV–visible spectroscopy, and high-resolution transmission electron microscopy (HRTEM). Both undoped and doped materials exhibit frequency-dependent permittivity, which increases with a decrease in the frequency, and attain very high values of 105 order at the low-frequency end (∼10 Hz). The doping of TiO2 with La3+/Cu+ has a strong influence on its dielectric behavior, and the permittivity of doped samples increases significantly compared to that of undoped samples. The crystal phase of TiO2 (rutile) remains unaffected even after La3+/Cu+ doping, as evidenced from XRD analysis. There is a bathochromic shift (red shift) of the UV–visible peak due to La3+/Cu+ doping in TiO2. Three different ceramic/polymer composites are prepared using three types of nanoparticles (TiO2, La-TiO2, Cu-TiO2) using a poly(dimethylsiloxane) elastomer as the base matrix. These flexible composites show some unique features like good temperature- and frequency-independent dielectric properties, thereby making them suitable candidates for flexible electronic materials. Further, their processing can be accomplished at low temperature (∼150 °C) and is more economical compared to ceramic dielectrics.