PNNL

Abstract

Introducing structural distortion and defects by doping, nanostructuring, or thermal treatment of oxide materials is one route of enhancing their performance for use in energy technologies such as photocatalysis, photovoltaics, and energy storage. Metastable brookite is a promising photocatalyst relative to the other thermodynamically stable polymorphs of earth-abundant TiO2. In this work, a facile thermal annealing approach is employed to promote the formation of predominantly brookite-phase films and regulate the brookite lattice distortion to enhance charge separation, ultimately directed towards enhancing photocatalytic activity. Rietveld Refinement analysis of x-ray diffraction patterns and peak shifts in Raman spectra revealed structural distortions of the brookite lattice. Structural defects including lattice gliding, dislocations, stacking faults, and twin boundaries were observed in the film by scanning transmission electron microscopy. First-principles simulations reveal how these lattice distortions associated with stacking faults correlate with increased photocatalytic activity of brookite. This study provides insight into microstructural tuning of metastable phases to enhance their unique functionalities.