In-situ Raman spectroscopy of BaTiO3 particles for tetragonal–cubic transformation Original Research Article

Tetragonality of the hydrothermally synthesized BaTiO3 particles were analysed by X-ray diffractometry (XRD) and Raman spectroscopy in comparison with the commercial BaTiO3 particles. The BaTiO3 particles were synthesized by hydrothermal reaction in supercritical water with the variation of reaction time for 8 ms, 2 s and 2 h. The reactants of TiO2 sol and Ba(OH)2 solution were used as starting materials and that was heated up to 400 °C under the pressure of 30 MPa. The XRD patterns and Raman spectra revealed that the crystal phase of the obtained particles for 2 s and 2 h was tetragonal BaTiO3, while that for 8 ms was cubic BaTiO3. The relation between crystal phase and particle size was discussed. Primarily particle size of the BaTiO3 particles determined by means of BET surface area increased with an increase in the reaction time from 10 nm to over 100 nm. Intensity of Raman band at 305 cm−1 increased with the particle size, indicating that the tetragonality is prominent for the highly crystalline BaTiO3 particles. Tetragonal to cubic phase transition was observed in-situ Raman spectra under air conditions where Curie temperature was between 100 and 150 °C.