Characterization of Submicron Particles of Tetragonal BaTiO₃

Abstract

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.

Low temperature synthesis of tetragonal BaTiO3 by using molten salt

“…The T C was somewhat lower than the published value (132°C), 24) and this value agreed well with that for 500 nm size BT powder prepared by hydrothermal reaction. 8) These results suggest that tetragonal BT by this work has similar character to 500 nm size BT powder prepared by hydrothermal reaction. 8) It was reported that mixed salt (50 + 50) of BaCl 2 and Ba(NO 3 ) 2 melted at about 500°C.…”

“…8) These results suggest that tetragonal BT by this work has similar character to 500 nm size BT powder prepared by hydrothermal reaction. 8) It was reported that mixed salt (50 + 50) of BaCl 2 and Ba(NO 3 ) 2 melted at about 500°C. JCS-Japan that the morphology of the starting compound did not hold and cubic shape particles were formed during this method.…”

“…It was reported that the lattice parameters for ³30¯m size single crystal were a = 3.9998(8) and c = 4.0180(8) ¡ (c/a = 1.0046) which were determined by single crystal X-ray diffraction data. 23) Those for 430 nm size BT fine powder prepared from BaTiO(C 2 O 4 )·4H 2 O were a = 3.99900 (8) and c = 4.03265(9) ¡ (c/a = 1.00842) which were determined by high resolution powder neutron diffraction data. 24) The lattice parameters for BT powder obtained by this work were good agreement with those (a = 3.9940(3) and c = 4.0357(5) ¡ (c/a = 1.0104)) for 500 nm size BT powder prepared by hydrothermal reaction.…”

“…24) The lattice parameters for BT powder obtained by this work were good agreement with those (a = 3.9940(3) and c = 4.0357(5) ¡ (c/a = 1.0104)) for 500 nm size BT powder prepared by hydrothermal reaction. 8) From the chemical analysis no potassium atom was detected and the Ba/Ti ratio in the tetragonal BaTiO 3 was 1.00. As shown in Fig.…”

Crystallization, phase evolution and ferroelectric properties of sol–gel-synthesized Ba(Ti0.8Zr0.2)O3–x(Ba0.7Ca0.3)TiO3thin films

“…The cubic perovskite structure inherently has no Raman active modes, and eight Raman active modes are expected for the noncentrosymmetric tetragonal structure, 3A 1g + B 1g + 4E g . 31 The Raman spectra of the BZT-0.5BCT sintered at different temperatures are shown in The band at 520 cm À1 has been observed in both the cubic and tetragonal phases of BTO and was conclusively assigned to scattering from the fundamental transverse component of the optical (TO) mode of A1 symmetry. 32 Because rst-order Pm 3m Raman scattering is symmetry-forbidden in the centrosymmetric space group, the activation of these phonons has been attributed to the presence of non-centrosymmetric regions in which the titanium (zirconium) atom is displaced from the center of the TiO 6 (ZrO 6 ) octahedra.…”