Mössbauer Studies of the SrTiO3:Fe57System

Mössbauer studies of the SrTi${\mathrm{O}}_3$: ${\mathrm{Fe}}^{57}$ system used as an absorber have shown that iron enters the SrTi${\mathrm{O}}_3$ lattice substitutionally at the ${\mathrm{Ti}}^{4+}$ site in its high-spin ferric state and is usually associated with a charge-compensating oxygen vacancy in agreement with the EPR evidence. On firing these samples in hydrogen, the quadrupole-split spectrum of ${\mathrm{Fe}}^{3+}$ associated with an oxygen vacancy transforms into a Zeeman-split spectrum with hf field and isomer shift characteristic of iron metal, indicating the formation of colloidal iron. Vacuum firing of the original air-fired samples tends to convert part of the ${\mathrm{Fe}}^{3+}$ ions into ${\mathrm{Fe}}^{2+}$ through the creation of more oxygen vacancies. The stages through which atomically dispersed ${\mathrm{Fe}}^{3+}$ ions are converted into colloidal iron on hydrogen firing and vice versa have been indicated.