Multi-frequency and pulsed electron paramagnetic resonance provided a sensitive spectroscopic tool to elucidate the defect structure of transition-metal doped perovskite oxides, as well as to monitor dynamic processes of oxygen vacancies in these materials. In this regard, high-frequency electron paramagnetic resonance spectrometers and pulsed electron paramagnetic resonance techniques such as the hyperfine sub-level correlation experiment may now routinely be used for dedicated investigations, providing considerably more insight than the application of standard continuous-wave electron paramagnetic resonance. Recent results include the formation of defect complexes between acceptor-type transition-metal centers with either one or two oxygen vacancies for the reason of charge compensation. Furthermore, such defect complexes follow the domain switching upon poling ferroelectric compounds with correspondingly high electric fields. On the other hand, multivalent manganese functional centers provided trapping centers for electronic and ionic charge carriers such that valency altered acceptor states or defect complexes were formed. Additionally, the trapping of charge carriers at the intrinsic 'reduced' B-site ions, and , could be observed by means of electron paramagnetic resonance spectroscopy.

Structural and Dynamic Properties of Oxygen Vacancies in Perovskite Oxides -Analysis of Defect Chemistry by Modern Multi-Frequency and Pulsed EPR Techniques. R.A.Eichel: Physical Chemistry and Chemical Physics, 2011, 13[2], 368-84