Study of structural and photoluminescent properties in barium titanate nanocrystals synthesized by hydrothermal process

Nanocrystalline barium titanate was synthesized by hydrothermal technique at ambient pressure and at temperatures less than 100°C. A temperature of 80° was found to be the optimum synthesizing temperature. The lattice vibration, microstructures and photoluminescence were examined by X-ray diffraction and Raman spectroscopy. The grain sizes ranging from 24 to 48 nm were obtained under heat treatment, from X-ray patterns via Scherrer formula. The critical size of 48 nm was found, below which the ferroelectric phase vanishes. Small tetragonality c/a ratio was found to be 1.003, causing a weakening of ferroelectricity. Strong photoluminescence spectrum centered at 696 nm was observed with the origin being attributed to charge transfer via intrinsic defects inside oxygen octahedron. Strengthening in PL spectra with increasing both annealing temperature and time, is related to the increase in oxygen vacancies and the grain size in the nanocrystal barium titanate.