Étude structurale par rayonnement synchrotron de superréseaux d'oxydes pérovskites

Abstract
Perovskite oxides are analyzed by using high resolution synchrotron radiation diffraction. The diffraction profiles are fitted, taking into account the structural and chemical disorders which depart from the ideal defect-free superlattice. Two types of superlattices, (BaTiO₃/SrTiO₃)₁₅ and (La_0.7Sr_0.3MnO₃/SrTiO₃)₁₅, are synthesized by metal-organic chemical vapor deposition (MOCVD) on oriented Nb-doped SrTiO₃ substrates. High-angle diffraction data show the excellent crystallinity and epitaxy of the films. For the (BaTiO₃/SrTiO₃)_n multilayers we observe a pseudo tetragonal symmetry with no difference between a and b axes, and they present a significant strontium/baryum interdiffusion. The (La_0.7Sr_0.3MnO₃/SrTiO₃) multilayers and their substrates almost have the same a=b parameter. Along the c axis, La_0.7Sr_0.3MnO₃ and SrTiO₃ have different lattice parameters. The crystallographic coherence of the stacking is higher in these samples.