Esr of Iron Defects in Strontium-Titanate

Three new Fe defect complexes were identified by electron spin resonance in Fe doped crystals of SrTiO3. One of these, Fe(3+)rh, occurs, in the as-grown crystals and may be characterized as an Fe(3+) cubic center with rhombic fine structure splittings. When the Fe doped crystals were reduced the Fe(3+)rh centers disappear, and a new non-Kramers S=2 system in tetragonal symmetry was produced. This defect was identified as Fe(2+)-V sub O. Optical excitation of the reduced samples repopulated the Fe(3+)rh centers and produced a new Kramers S=3/2 system in tetragonal symmetry identified as Fe(1+)-V sub O. A simple model for the appearance of these multiple charges in the 3eV band gap based on the polarization of the oxygen ligands was investigated.