Mössbauer Effect forFe57in Ferroelectric BaTiO3. II. The Vacancy-Impurity Associated State

In the study of ferroelectric BaTi${\mathrm{O}}_3$ using the ${\mathrm{Fe}}^{57}$ Mössbauer probe, a variety of environments are encountered by the impurity probes. Velocity spectra have been analyzed to show that the ${\mathrm{Ti}}^{4+}$ substitution by the probe ${\left({\mathrm{Co}}^{57}\right)}^{2+}\to {\left({\mathrm{Fe}}^{57m}\right)}^{3+}$ or stable ${\left({\mathrm{Fe}}^{57}\right)}^{3+}$ results generally in localized charge-compensating oxygen vacancies. Polarization experiments show that the impurity-vacancy complexes are rotatable. The oxygen vacancies are believed to be of the axial type (OI oxygens) in tetragonal BaTi${\mathrm{O}}_3$. Large nonstoichiometry in reduced samples has been shown to induce an ${\mathrm{Fe}}^{2+}$ state.