Crystal structure of barium titanate fine particles including Mg and analysis of their lattice vibration

Fine barium titanate crystallites with various Mg contents were prepared by a hydrothermal method. These particles were spherical single crystallites with an average size of about 63 nm, regardless of Mg contents from 0 to ab out 0.15 wt%. It was confirmed that Mg replaced substitutionally on Ti site . On the refinement of the crystal structure with a Rietveld method, the cr ystal structure of the particles without Mg was tetragonal with a tetragona lity of 1.0015 while those including Mg approached from tetragonal to cubic gradually with increasing Mg content. On the other hand, a Raman measureme nt indicated that the local structure remained tetragonal regardless of Mg contents. Moreover, the resonance frequency for each phonon mode was indepe ndent of Mg contents while their damping factor increased with increasing M g content, which suggested that state of the phonon became more unstable wi th increasing Mg content. Therefore, the lattice defects induced by Mg into the barium titanate particles can give the phonon a similar effect to that of temperature in barium titanate single crystal. (C) 2000 Kluwer Academic Publishers.