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 (00 l ) 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.