抄録
The stability of several compounds in the system BaO-TiO2 coprecipitated from the alkoxides were investigated. The samples in which the mole ratios of BaO to TiO2 were 2/1, 1/1, 1/2, 1/3, 1/4, 2/9, 1/5 and 1/9 were prepared by the simultaneous hydrolysis of barium isopropoxide and titanium isopropoxide. On the as-prepared specimens, only 1/1 specimen crystallized as a single phase of cubic BaTiO3, 2/1 was composed of cubic BaTiO3 and Ba(OH)2·H2O, and all others in the TiO2-rich region were of amorphous forms. It is suggested that Ba2+ in the 1/1 solution reacts as a strong Lewis acid and directly combines with Ti(OiPr)62-, and a double alkoxide, Ba[Ti(OiPr)6] is formed in isopropanol solution. In the TiO2-rich region, the polymerization takes place on the formation of Ti-O-Ti bridge following the hydrolysis of Ti(OiPr)4, resulting in the precipitation of amorphous phase.
By heating at 800°C of 1/2 and 1/5 specimens, the single phases of BaTi2O5 and BaTi5O11 were formed respectively. Thus far the single phases of these compounds have not been obtained. Since BaTi2O5 and BaTi5O11 begin to decompose above 1200°C, they are considered to be a low temperature form or a metastable form.
