Résumé
We have used x-ray diffraction and Raman spectroscopy over a broad temperature range (90K⩽T⩽900K) to study the structural and dynamical behavior of [PMN(1−x)Λ/(PbTiO3)xΛ]10 superlattices (x=0.2,0.5,0.8) (where PMN is PbMg1∕3Nb2∕3O3), which were epitaxially grown with a nominal wavelength Λ of 130Å by pulsed laser deposition on MgO substrates buffered with La0.5Sr0.5CoO3. We present a comparison of the results obtained on these superlattices with the temperature evolution of three fictitious superlattices constructed using the temperature-dependent data obtained on individual PbTiO3 and PbMg1∕3Nb2∕3O3 epitaxial thin films. From this study, we conclude that the PMN layers in superlattices retain the structural characteristics, including the tetragonal distortion, of relaxor thin films. The PbTiO3 layers exhibit in-plane polar orientation at all temperatures. X-ray diffraction shows the stabilization, due to biaxial stress, of the ferroelectric order up to at least 873K in the PbTiO3 layers (TC=763K in bulk). The tetragonal symmetry and ferroelectric order of the PbTiO3 layers, as well as the relaxorlike behavior of the PMN layers, are confirmed by Raman spectroscopy.