チタン酸バリウム微粉末の表面吸着種

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The submicron samples of barium titanate were prepared by (1) the hydrolysis of titanium iso-propoxide in barium hydroxide solution (BT-I), (2) the simultaneous hydrolysis of barium iso-propoxide and titanium iso-propoxide (BT-II), and (3) the grinding of barium titanate prepared from barium carbonate and titanium oxide (BT-III) in iso-propyl alcohol or in air, and the species adsorbed on their surface were examined by means of TGA, DTA and IR spectroscopy.
On the as-prepared BT-I having the particle size of 100 to 300Å, the surface species identified were the hydrogen-bonded hydroxyl group, iso-propyl or iso-propoxy groups, the carboxyl group and the carbonate ion. Adsorbed alcohol began to be removed at about 200°C and all species disappeared completely above 800°C.
On the as-prepared BT-II having the particle size of about 100Å, the concentration of the iso-propoxy group and the carboxyl group seemed to be higher than those of as-prepared BT-I. Since the carbonate ion was not found on the as-prepared surface but appeared on heating it at 500°C, it is suggested that the carbonate ion would be formed from the carboxyl group.
When the BT-III was ground in iso-propyl alcohol, its IR spectra were similar to those of the as-prepared BT-I, but when ground in air, the large broad doublet spectra appeared in the stretching vibration region of carbonate salt, suggesting the monodentate bonding of the carbonate ion on the barium ion site.
The difference of the surface species and of the bonding character are considered to be related to the preparation method, the character of the surface ions, and the surface activity or the space charge layer near the surface of ferroelectric fine powder.