Monoclinic symmetry of twin-free nanocrystals in the BiScO3 -PbTiO3 solid solution as revealed by aberration-corrected TEM
Résumé
Ferroelectric perovskite solid solutions with morphotropic phase boundary MPB have been studied extensively as best candidates for electromechanical transduction due to their exceptionally high piezoelectric coefficients. However, despite the high number of publications about these oxides, there is still ambiguity about the actual symmetry of the phases at the MPBs. Here, we present a detailed analysis of the crystalline structure of 0.39BiScO 3-0.61PbTiO 3 twin free nanocrystals, using the combination of aberration-corrected high-resolution electron microscopy and multislice simulations. Our study indicates the presence of a monoclinic symmetry for crystals with an average size of 15 nm. This is strong evidence in favor of the actual existence of this polymorph at the MPB, which has been recently questioned. It also shows that perovskite distortion is still present in nanocrystals, which is important from the point of view of the size limit of ferroelectricity and consistent with previous electrical measurements in nanostructured ceramics.
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