Dept. of Materials Science and Engineering
Oregon Graduate Center
Polytitanates in the BaO- TiO2 system with Ba:Ti ratios ranging from 1:2 to 1:5 were prepared using a low temperature technique developed by Pechini. The samples were heated at 600 to 1300Â°C in oxygen. Room temperature Raman spectroscopy was used to investigate the phase relations in this system. Results of this study indicate the following: except for BaTi4O9, the powders of these compounds were amorphous when heated at 600Â°C for 4hrs; the compound BaTi2O5 is a low temperature stable phase; Ba6Ti17O40 forms only at temperatures above 1100Â°C; Ba4Ti13O30 does not form below 1000Â°C; the single phase BaTi4O9 structure was observed at 1200Â°C'; the Ba2Ti9O20 phase is obtained only after long heat treatment at 1200Â°; BaTi5O11 was stable up to 1200Â°C, at which it decomposes into Ba2Ti4O20 and TiO2. After determination of stability relationships in this system, the electrical conductivities of these compounds were examined as a function of temperature and oxygen partial pressure. For all the temperatures (850-1150Â°C) studied, the conductivities of these compounds increased with decreasing oxygen partial pressure resulting in n-type properties throughout the whole P[subscript O2] range (10[superscript -19 - 1atm). The P[subscript O2] dependencies of the electrical conductivity were found to be linear for an extensive range of oxygen partial pressures. On the basis of structural considerations the conductivity data was described by a majority defect model consisting of both singly and doubly ionized oxygen vacancies. For lower oxygen partial pressure values a drastic change in the electrical conductivity was observed. This is believed to result from increasing defect interaction for larger departures from stoichiometry. A defect model based on this interaction is proposed to account for the observed sharp change in the electrical conductivity values.
Javadpour, Jafar, "Phase stability and defect structure determination of polytitanate compunds in the BaO-TiO2 system" (1988). Scholar Archive. 252.