Powder samples were synthesized by heat-treating citrate polyester resins (500C, 8h). Raman spectroscopic and X-ray powder diffractometry data indicated the presence of a high-temperature hexagonal phase at room temperature. On the other hand, high-resolution transmission electron microscopy indicated that the peaks which were attributed to the above phase in Raman and X-ray diffraction spectra could originate from stacking faults in the particles. Indeed, only tetragonal BaTiO3 particles which contained numerous (111) stacking faults were found. The stacking faults could thus generate the satellite peaks which corresponded to the high-temperature hexagonal structure in X-ray and Raman spectra. Ions of Ti3+ were found, and it was suggested that the crystal chemistry of BaTiO3 could alter in order to retain a local charge balance. The presence of stacking faults was therefore accompanied by a change in the oxidation state of the Ti atoms. The results did not confirm a reported size effect, upon stabilization, of high-temperature hexagonal BaTiO3 at room temperature.

W.S.Cho, E.Hamada, K.Takayanagi: Journal of Applied Physics, 1997, 81[7], 3000-2