Structure and Microstructure of Epitaxial Sr4Fe6O13(plus_minus) Films on SrTiO3

The crystal structure and the microstructure of epitaxial Sr4Fe6O13(plus_minus) thin films grown on a singlecrystal SrTiO3 substrate by PLD have been investigated. A combination of electron diffraction and high-resolution microscopy allows us to refine the structure and to identify an incommensurate modulation in the Sr4Fe6O13(plus_minus)(delta) films. The incommensurate structure (q =(alpha) am* 0.39(alpha)am*, superspace group Xmmm((alpha)00)0s0) can be interpreted as an oxygen-deficient modification in the Fe2O2.5 double layers. Moreover, it is shown that the experimentally determined component of the modulation can be used consistently to estimate the local oxygen content in the Sr4Fe6O13(plus_minus)(delta) films. The compound composition can therefore be described as Sr4Fe6O12+2 and the value = 0.39 corresponds to a Sr4Fe6O12.78 composition. The misfit stress along the Sr4Fe6O13(plus_minus) (delta)\SrTiO3 interface is accommodated via both elastic deformation and inelastic mechanisms (misfit dislocations and 90 rotation twins). The present results also suggest the existence of SrFeO3 perovskite in the Sr4Fe6O13(plus_minus)(delta) films.