Barium titanate (BaTiO3) 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 BaTiO3 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 BaTiO3 powders exhibited small strains. Differential scanning calorimetry showed a decrease in enthalpy of transition (ΔH) values with particle size. The particle size dependence on ΔH 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.

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The sintering behavior of hydrothermally synthesized cubic and tetragonal BaTiO3 powders was studied as a function of temperature. In addition, the dielectric properties of the sintered samples were examined from room temperature to 200°C at a frequency of 1 kHz. The influence of powder characteristics and sintering temperature on the microstructure development and dielectric properties were investigated. It was found that tetragonal powders showed limited grain growth and higher final density upon sintering, whereas the cubic powder exhibited abnormal grain growth and lower density. This was attributed to more disperse and homogeneous particles in the tetragonal powders with fewer defects, as compared to the cubic powder. Correlations between the microstructure and the dielectric properties were developed. As expected, samples with finer grain size and higher density exhibited higher dielectric constant and lower loss.

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