Structural and dynamic properties of oxygen vacancies in perovskite oxides—analysis of defect chemistry by modern multi-frequency and pulsed EPR techniques

Abstract

Multi-frequency and pulsed electron paramagnetic resonance (EPR) provides 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 EPR spectrometers and pulsed EPR techniques such as the hyperfine sublevel correlation experiment (HYSCORE) may now routinely be used for dedicated investigations, providing considerably more insight than the application of standard continuous-wave EPR. 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, multi-valent manganese functional centers provide trapping centers for electronic and ionic charge carriers (e', ) such that valency altered acceptor states or defect complexes are formed. Additionally, the trapping of charge carriers at the intrinsic 'reduced' B-site ions, and , can be observed by means of EPR spectroscopy.

Spectroscopic study of the electric field induced valence change of Fe-defect centers in SrTiO3

“…It should be mentioned that the Fe 4+ center created in the anodic region is a ''non-Kramers'' ion due to the large contribution of the d 4 configuration to the ground state, and therefore does not appear in the spectra. 25 There are no other EPR-active impurity centers with significant contributions to the EPR spectra.…”

Antiferroelectric-like properties and enhanced polarization of Cu-doped K0.5Na0.5NbO3 piezoelectric ceramics

“…13) and is subsequently confirmed by the EPR spectrum. 14,15 Non-switchable DCs that are aligned opposite to the spontaneous polarization (P s ) direction provide the driving force for domain backswitching after the removal of the external electric field, similar to the antiferroelectric behavior. For KNN10, the DCs would be quite mobile at temperatures above 130 C, and hence the external dc field resulted in a redistribution of the defects and the consequential development of E ib .…”

First-principles study of band gap engineering via oxygen vacancy doping in perovskiteABB′O3solid solutions

“…Although there have been a few recent spectroscopic breakthroughs in locating oxygen vacancies 9 , the atomic-scale resolution of oxygen vacancy positions is still difficult to achieve experimentally. This makes density functional theory (DFT) calculations a natural approach for studying vacancies, due to the combination of atomic scale resolution, computational efficiency, and accuracy.…”