Date

January 1988

Document Type

Dissertation

Degree Name

Ph.D.

Department

Dept. of Materials Science and Engineering

Institution

Oregon Graduate Center

Abstract

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 1300°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 600°C for 4hrs; the compound BaTi2O5 is a low temperature stable phase; Ba6Ti17O40 forms only at temperatures above 1100°C; Ba4Ti13O30 does not form below 1000°C; the single phase BaTi4O9 structure was observed at 1200°C'; the Ba2Ti9O20 phase is obtained only after long heat treatment at 1200°; BaTi5O11 was stable up to 1200°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 (850-1150°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.

Identifier

doi:10.6083/M4DZ0688

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