Characterization of Submicron Particles of Tetragonal BaTiO₃

Barium titanate (BaTiO 3 ) powders of varying particle sizes were grown under hydrothermal conditions at a temperature of 240 °C. This was accomplished by varying the hydroxide concentration of the reaction medium as well as the time required for synthesis. The spectroscopic, thermal, and microscopic characteristics of three BaTiO 3 powders with average particle sizes 0.09, 0.3, and 0.5 μm were examined. Transmission electron microscopy indicated that all the particles were of single domain. The powder with smallest particle sizes (0.09 μm) contained unreacted titanium dioxide, whereas the larger particles (0.3, 0.5 μm) were pure barium titanate. The Raman spectra showed that all these crystals were tetragonally distorted. Infrared spectra showed primarily Frohlich modes, whose intensities also decreased with particle size. Analysis of the broadening of the powder diffraction patterns suggested that the BaTiO 3 powders exhibited small strains. Differential scanning calorimetry showed a decrease in enthalpy of transition (Δ H ) values with particle size. The particle size dependence on Δ H is attributed to the transition from a polar to a nonpolar state which occurs due to the bulk dipoles disordering due to interaction with the surface dipoles.