Local structures in ceria-based materials were investigated by UV resonance Raman spectroscopy using a 363.8 nm laser line for the first time. In the spectra of a highly crystalline and undoped ceria, overtone LO series are clearly detected due to the multiphonon relaxation by the UV resonance Raman effect. Gd 3+ doping in ceria additionally activates the disorder bands that are attributable to lattice spaces with or without an oxygen vacancy. The crystal size dependency of the UV Raman spectra suggests that Ce 3+ ions preferably form the MO 8 -type (M ) Ce 3+ ) complex in the undoped ceria nanoparticles and are eliminated by oxidation while heating in air. Gd 3+ ions also tend to form a MO 8 -type complex in the nanocrystalline ceria matrix. However, they diffuse to form the more thermodynamically stable defect clusters that accompany the grain growth upon heating.

The cross-substitution effect of tantalum on the photocatalytic water oxidation activity of BaNbO2N crystals grown by a flux method was investigated.

Photocatalytic overall water splitting on (oxy)nitrides under visible light is one of the interesting approaches to fulfill the growing demand for clean and renewable energy. The improvement of the fabrication method is however important for reducing the defect density of (oxy)nitride crystals. The present study aims to investigate the direct growth of the LaTiO 2 N (LTON) crystallites with less defect density by an NH 3 -assisted flux method and to demonstrate the visible-light-induced photocatalytic water oxidation activity in relation to their crystallite morphology. Single-phase LaTiO 2 N crystallites (average size of 120 ± 39 nm) in round shape with smooth surface and high crystallinity were grown by an NH 3 -assisted flux method using the KCl flux with the solute concentration of 5 mol % at 950 °C for 10 h. The photocatalytic water oxidation activity of bare and CoO x -loaded LaTiO 2 N crystallites grown directly by an NH 3 -assisted flux method (1-step-LTON) was evaluated under visible light by comparing with the LaTiO 2 N crystallites fabricated by a two-step method (2-step-LTON), converting La 2 Ti 2 O 7 to LaTiO 2 N by high-temperature nitridation. Within the first 2 h of the photocatalytic water oxidation half-reaction, the O 2 evolution rates of bare and CoO x -loaded 1-step-LTON crystallites were 82 µmol·h -1 and 204 µmol·h -1 , respectively, which are much higher than that of bare and CoO x -loaded 2-step-LTON crystallites (37 µmol·h -1 and 177 µmol·h -1 ) due to less defect density of the LaTiO 2 N crystallites achieved by a direct fabrication route using KCl flux. An NH 3 -assisted flux growth is a promising route for the direct fabrication of the LaTiO 2 N crystallites with less defect density that is beneficial for the enhancement of photocatalytic water oxidation half-reaction.