Chemical states, roles and interrelations of additives in BaTiO3 ceramics

Chemical states of Mn in BaTiO3 and interactions between Mn and other dopants were studied mainly by chemical analysis and ESR spectroscopy. Chemical analysis showed that the average valency of Mn doped into BaTiO3 was about 3.4, indicating the occurrence of a significant concentration of oxygen vacancy. The average valency of Mn was scarcely affected by codoping of an equimolar amount of La with Mn, but was markedly lowered by addition of Si. It was assumed that stabilization of La segregated to the grain-boundary region due to La-Mn interaction resulted in suppression of the cation vacancy formation and eventually in protection of adsorbed oxygen ions at the grain boundaries. ESR analysis showed that La3+-Mn3+ associate was a strong trap center compatible with Mn4+. The mean valency of Mn in the grain-boundary region of Mn- and La-codoped BaTiO3 was significantly lower than that in the grain interior.