Synthesis and characterization of potassium bismuth titanate inverse opal photonic crystals by sol–gel technique

Inverse opal photonic crystals of lead-free ferroelectric potassium bismuth titanate, K0.5Bi0.5TiO3 (described as KBT) were synthesized by sol–gel technique in combination with self-assembly method. Opal template was self-assembled from suspension of monodisperse polystyrene (PS) microspheres with a mean diameter of 400 nm via a vertical deposition process. KBT sol was prepared by mixing bismuth nitrate and potassium carbonate dissolved in acetic acid and ethylene glycol, and tetrabutyl titanate in acetic acid. After infiltrating the KBT sol into the opal template, KBT inverse opal photonic crystals were formed by a series of heat-treatments. X-ray diffraction (XRD), scanning electron microscopy (SEM) and optical microscopy (OM) were utilized to characterize the structure and optical properties of the KBT samples, and a photonic bandgap around 500 nm was observed by micro-region reflectance spectra.