Local conductivity and the role of vacancies around twin walls of (001)−BiFeO3 thin films

Abstract

BiFeO3 thin films epitaxially grown on SrRuO3-buffered (001)-oriented SrTiO3 substrates show orthogonal bundles of twin domains, each of which contains parallel and periodic 71 o domain walls. A smaller amount of 109 o domain walls are also present at the boundaries between two adjacent bundles. All as-grown twin walls display enhanced conductivity with respect to the domains during local probe measurements, due to the selective lowering of the Schottky barrier between the film and the AFM tip (see S. Farokhipoor and B. Noheda, Phys. Rev. Lett. 107, 127601 (2011)). In this paper we further discuss these results and show why other conduction mechanisms are discarded. In addition we show the crucial role that oxygen vacancies play in determining the amount of conduction at the walls. This prompts us to propose that the oxygen vacancies migrating to the walls locally lower the Schottky barrier. This mechanism would then be less efficient in non-ferroelastic domain walls where one expects no strain gradients around the walls and thus (assuming that walls are not charged) no driving force for accumulation of defects.

Applications of piezoresponse force microscopy in materials research: from inorganic ferroelectrics to biopiezoelectrics and beyond

“…Using PFM, Catalan et al reported that ferroelectric domains in BFO thin films are not well described by the LandauLifschitz-Kittel scaling law satisfied by purely ferroelectric films, exhibiting a scaling behaviour closer to that of magnetic materials. 131 PFM has also been central in the studies on ferroelectric domain wall conduction 118,132 and photovoltaicity 119, 120 as a way to distinguish between the three types of domain walls present in BFO. The ferroelectric polarisation switching characteristics of BFO has been the focus of numerous studies, as discussed in Sect.…”

Nanoscale studies of ferroelectric domain walls as pinned elastic interfaces

“…The ability to non-invasively identify these very localised features at the domain walls could be especially interesting when coupled with an investigation of their functional properties [74]. In particular, given that oxygen vacancies [142,143] increase domain wall conduction, and dislocation cores are associated with a very high presence of oxygen vacancies [144,139], exploring the link between multi-affinity and domain wall current levels could be a promising research pathway.…”

Towards reversible control of domain wall conduction in Pb(Zr0.2Ti0.8)O3 thin films

“…11 Varying the growth conditions of such films to induce different oxygen vacancy densities was found to modulate the domain wall conductance by over an order of magnitude. 12,13 The defect states can also be photo-activated, temporarily inducing, or enhancing domain wall currents by supra-bandgap illumination. 14,15 Here, we show that by using a moderate temperature, ultrahigh vacuum (UHV) annealing and ambient exposure, domain wall currents in PZT thin films can be reversibly controlled, allowing either conductive or insulating behavior, stable over the multi-week period of measurement.…”