Microstructure and local electrical behavior in [(Nd(2)Ti(2)O(7))(4)/(SrTiO(3))(n)](10) (n = 4–8) superlattices

Artificial [(Nd(2)Ti(2)O(7))(4)/(SrTiO(3))(n)](10) superlattices (n = 4 and 8) were successfully epitaxially grown on SrTiO(3) substrates by pulsed laser deposition using the in situ high energy electron diffraction reflection diagnostic. The crystallographic relationships between Nd(2)Ti(2)O(7) (NTO) and SrTiO(3) (STO) (layers and substrate) were: [100](NTO)//[001](STO), [010](NTO)//[1̄10](STO), and (00l)(NTO)//(110)(STO). Nanoscale current variation was detected on both superlattices, with the (NTO(4)/STO(4))(10) heterostructure showing a higher density. The (NTO(4)/STO(4))(10) sample did not show a piezoelectric response when measured by piezo-force microscopy (PFM), while ambiguous piezoactivity was observed on the (NTO(4)/STO(8))(10) superlattice. Scanning transmission electron microscopy energy dispersive spectroscopy analysis showed the diffusion of Nd(3+) cations on Sr(2+) sites in SrTiO(3) structure into the multilayers, which was more pronounced when the value of n was lower. These particular nanoscale electrical behaviors, evidenced by electrical conducting channels and misleading PFM signals, were mainly attributed to the presence of oxygen vacancies in the SrTiO(3) layers at higher concentrations near the interface and to the mixed valence state of the titanium (Ti(3+)/Ti(4+)). This work showed the strong influence of interface structure on nanoscale electrical phenomena in complex oxide superlattices.