High-Quality Brookite TiO2 Flowers: Synthesis, Characterization, and Dielectric Performance

Abstract

High-quality brookite flowers were fabricated via a facile solution chemistry technique. The synthetic conditions to the flower-like brookite were monitored by a series of time-resolved experiments and further optimized by adjusting the concentrations of the Na+ and OH− species involved in the reaction system. Careful sample characterizations by the combined techniques of X-ray diffraction, Raman, high resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and electron paramagnetic resonance spectra indicate the formation of highly phase-pure and well-crystallized brookite with an extremely low defect concentration. Different from the natural brookite mineral with an indirect transition (Zallen, R.; Moret, M. P. Solid State Commun. 2006, 137, 154), the present high-quality brookite flowers showed a direct transition with a bandgap energy of 3.4 ± 0.1 eV, which is larger than those of its two other polymorphs, that is, a direct band gap of 3.0 ± 0.1 eV for rutile and indirect band g...