A++/Ti Nonstoichiometry in Alkaline Earth Titanates, ATi03
Ternary oxides offer the possibility of variations in the ratios of the two metallic constituents as well as in the metal-nonmetal ratios. The extent of this cation-cation nonstoichiometry, and its effect on material properties, is of interest because numerous useful ferroelectric, piezoelectric, magnetic, and electrooptic materials are found among the ternary oxides. When significant cation-cation nonstoichiometry is tolerated in the single phase system, the resulting changes in ionic defect concentrations can affect charge and mass transport and oxidation-reduction equilibria. If the tolerance for nonstoichiometry is exceeded, second phases will be present that can also profoundly affect the material properties, e.g., if the second phase is liquid at the sintering temperature, densification rates and the resulting microstructure will be strongly influenced. This paper will discuss the cation-cation nonstoichiometry of the alkaline earth titanates having the perovskite structure, BaTi03, SrTi03, and CaTiO3. These compounds share the generic formula ABO3, and the structure is characterized by having two very different types of cation sites, a large, 12-coordinate A site, occupied by the alkaline earth ions, and a smaller, 6-coordinate, octahedral B site, occupied by the titanium. In the ideally pure, stoichiometric compounds, all equivalent lattice sites are completely occupied by the appropriate species.
KeywordsAlkaline Earth Perovskite Structure American Ceramic Society Ternary Oxide Acceptor Impurity
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