Structural characterization of thin films of the SrBi2Nb2O9 ferroelectric Aurivillius phase epitaxially grown on (110)SrTiO3

Aurivillius-phase SrBi(2)Nb(2)O9 (SBN) films grown by pulsed-laser deposition on (110)SrTiO3 are nearly (116) oriented as shown by their X-ray diffraction theta-2theta scans. A specific artifact, leading possibly to an erroneous deduction of a (115) and (116) mixture of orientations, has been highlighted. The films present a quite small mosaicity (omega-scan full width at half-maximum=0.2-0.5degrees). Sharp electron channeling patterns (ECPs) with the expected twofold symmetry are the signature of film epitaxy. These ECPs often display the superimposition of two individual patterns, rotated by 180degrees with respect to each other: two families of oriented SBN crystallites, rotated in the same way, coexist in the films. Indeed, from symmetry considerations at the film-substrate interface, these two families are a priori equiprobable. Similarly, two peaks, 180degrees shifted, are observed for the 0010 reflection phi scans and fully confirm this model. However, their relative intensity, which gives access to the quantitative distribution of the two families, shows that in many cases the two families do not present the same relative weight, in good correlation with the qualitative ECP observations, indicating a subtle asymmetrization at the nucleation or growth stage. The in-plane orientation is defined as: [(1) over bar 10](F) parallel to [001](S) and nearly [33 (1) over bar](F) or [(3) over bar(3) over bar1](F) parallel to [(1) over bar 10](S) (generating the two families). The film-substrate interfacial relationship is discussed, taking into account the possible facetting of the substrate surface and the occurrence of the (11 (7) over bar) SBN plane as twin boundary.