Hydrothermal conditions for the formation of tetragonal BaTiO3 particles from potassium titanate and barium salt

The formation of tetragonal BaTiO3 from K2Ti6O13 (K2T6) nanowires was examined under hydrothermal conditions at 100-240 degrees C. The morphology and the crystal structure of the BaTiO3 particles that grew via a dissolution-precipitation mechanism were controlled by the temperature and the concentrations of the NaOH and the K2T6. The degree of tetragonality of the formed BaTiO3 powders was quantitatively evaluated on the basis of a Rietveld crystal-structure refinement and compared with the results of Raman and DSC analyses. The powders consisted mainly of star-like BaTiO3 particles that formed at 100 degrees C and contained cubic (22%) and tetragonal (78%) phases with a low c/a value of 1.0042. The BaTiO3 particles changed their shape to dendritic and seaweed-like with an increase of temperature to 150 degrees C and 200-240 degrees C, respectively. According to the Rietveld analysis this increase of the temperature led to the formation of a tetragonal phase with a high c/a ratio (1.008-1.010), which dominated over the cubic and tetragonal phases with a low c/a (1.004-1.007). An increase in the K2Ti6O13 and NaOH concentrations was found to decrease the tetragonality of the formed BaTiO3 particles. The electron-diffraction patterns suggested a multidomain structure for the seaweed-like, mainly tetragonal, BaTiO3 particles. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.