Evidence of intergrowth in SrBi2Nb2O9 (SBN) thin films grown by PLD on (1 0 0)SrTiO3 in relation with the composition

Thin films of the fatigue-free ferroelectric material SrBi2Nb2O9 (SBN) have been epitaxially grown by pulsed laser deposition on SrTiO3(1 0 0) substrates. These films are fully c-axis oriented and show in-plane orientation as shown by X-ray diffraction in θ–2θ and ϕ-scan modes, as well as reflection high energy electron diffraction and electron channeling patterns. We have evidenced that the epitaxial growth is strongly affected by the Bi content of the target, and then of the film. A specific intergrowth mechanism is encountered in the case of Bi deficient films; it is based on the random stacking along the growth direction of layers with different c unit-cell constants. Cross-section high resolution transmission electron microscopy confirms this mechanism and shows that the two types of layers involved correspond essentially to the compounds with m=2 and 3 in the usual Aurivillius phases notation (Bi2O2)2+ (Srm−1NbmO3m+1)2−. By contrast, in near-stoichiometric films, a few stacking faults are observed whereas in both cases a quite perfect in-plane orientation is evidenced.