Elastic distortion determining conduction in BiFeO3 phase boundaries. Issue 47 (27th July 2020)

• Record Type: Journal Article
• Authors: Holsgrove, Kristina M.; Duchamp, Martial; Moreno, M. Sergio; Bernier, Nicolas; Naden, Aaron B.; Guy, Joseph G. M.; Browne, Niall; Gupta, Arunava; Gregg, J. Marty; Kumar, Amit; Arredondo, Miryam
• Is Part Of: RSC advances. Volume 10:Issue 47(2020)
• Page Start: 27954
• Page End: 27960
• Publication Date: 2020-07-27
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/d0ra04358c
• Languages: English
• ISSNs: 2046-2069

Abstract

Abstract : The localized crystallography of conducting and non-conducting phase boundaries in mixed-phase BiFeO3 is directly compared using scanning transmission electron microscopy techniques. Abstract : It is now well-established that boundaries separating tetragonal-like (T) and rhombohedral-like (R) phases in BiFeO3 thin films can show enhanced electrical conductivity. However, the origin of this conductivity remains elusive. Here, we study mixed-phase BiFeO3 thin films, where local populations of T and R can be readily altered using stress and electric fields. We observe that phase boundary electrical conductivity in regions which have undergone stress-writing is significantly greater than in the virgin microstructure. We use high-end electron microscopy techniques to identify key differences between the R–T boundaries present in stress-written and as-grown microstructures, to gain a better understanding of the mechanism responsible for electrical conduction. We find that point defects (and associated mixed valence states) are present in both electrically conducting and non-conducting regions; crucially, in both cases, the spatial distribution of defects is relatively homogeneous: there is no evidence of phase boundary defect aggregation. Atomic resolution imaging reveals that the only significant difference between non-conducting and conducting boundaries is the elastic distortion evident – detailed analysis of localised crystallography shows that the strain accommodation across the R–T boundaries is much more extensive in stress-written than in as-grown microstructures; this has a substantial effect on the straightening of local bonds within regions seen to electrically conduct. This work therefore offers distinct evidence that the elastic distortion is more important than point defect accumulation in determining the phase boundary conduction properties in mixed-phase BiFeO3 .