Optical studies of transparent ferroelectric strontium-barium niobate/silica nanocomposite

Abstract

Transparent ferroelectric strontium–barium niobate (SBN) doped silica nanocomposites were prepared via a modified sol–gel process. Their structural properties were characterized by x-ray diffraction and Raman spectroscopy. It was found that by annealing the nanocomposites at temperatures between 600 and 800 °C, pure tetragonal tungsten bronze phase SBN crystallites with sizes ranging from 8 to 23 nm were obtained. Differential scanning calorimetry measurement has indicated that nanometer size ferroelectric SBN has a reduced phase transition temperature compared with that of bulk SBN. Photoluminescence and optical transmission studies of these composites have revealed noticeable blueshifts in the emission band peak and the absorption edge, respectively. The refractive index of the nanocomposite annealed at 700 °C was measured by ellipsometry. The value obtained is larger than that of pure sol–gel derived silica but smaller than that of SBN crystal, and can be described by the Bruggeman effective medium approximation.