CHARACTERIZATION OF SUBMICRON PARTICLES OF TETRAGONAL BATIO3

Barium titanate (BaTiO3) powders of varying particle sizes were grown under hydrothermal conditions at a temperature of 240 degrees C. This was accomplished by varying the hydroxide concentration of the reactio n medium as well as the time required for synthesis. The spectroscopic , thermal, and microscopic characteristics of three BaTiO3 powders wit h average particle sizes 0.09, 0.3, and 0.5 mu m were examined. Transm ission electron microscopy indicated that all the particles were of si ngle domain. The powder with smallest particle sizes (0.09 mu m) conta ined unreacted titanium dioxide, whereas the larger particles (0.3, 0. 5 mu m) were pure barium titanate. The Raman spectra showed that all t hese crystals were tetragonally distorted. Infrared spectra showed pri marily Frohlich modes, whose intensities also decreased with particle size. Analysis of the broadening of the powder diffraction patterns su ggested that the BaTiO3 powders exhibited small strains. Differential scanning calorimetry showed a decrease in enthalpy of transition (Delt a H) values with particle size. The particle size dependence on Delta H is attributed to the transition from a polar to a nonpolar state whi ch occurs due to the bulk dipoles disordering due to interaction with the surface dipoles.