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

Nanocrystalline barium titanate was synthesized by hydrothermal technique a t ambient pressure and at temperatures less than 100 degreesC. A temperatur e of 80 degrees was found to be the optimum synthesizing temperature. The l attice vibration, microstructures and photoluminescence were examined by X- ray diffraction and Raman spectroscopy. The grain sizes ranging from 24 to 48 ran were obtained under heat treatment, from X-ray patterns via Scherrer formula. The critical size of 48 mn was found, below which the ferroelectr ic phase vanishes. Small tetragonality cla ratio was found to be 1.003, cau sing a weakening of ferroelectricity. Strong photoluminescence spectrum cen tered at 696 run was observed with the origin being attributed to charge tr ansfer 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 bari um titanate. (C) 2001 Published by Elsevier Science Ltd.