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Building Units and Intergrowths: Toward the Design of an Extended Family of Acentric Bi-Based Materials with Second Harmonic Generacy

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posted on 08.09.2009, 00:00 by Marielle Huvé, Marie Colmont, Julien Lejay, Patrick Aschehoug, Olivier Mentré
The concerted use of transmission electron microscopy and X-ray diffraction has been exploited to point out the existence of versatile 2D building units (BUs) able to organize in 3D regular intergrowths, on the basis of an extended series of new Bi oxophosphate materials. Here, the so-called BUs consist of ribbon-like polycations formed of the linkage of n O(Bi,M)4 tetrahedra along their width. Previous results about the relationships between short (n = 1 to 6) BUs and their specific HREM contrasts have been extended to longer BUs identified in this work (n = 8 to 12) in the inhomogeneous sample with the bulk-formula Bi6Li2Zn2P4O22. Seven new intergrowths between them (new materials), with PO4 interfacial species, have been fully rationalized, enabling the predictive design of future new materials. Finally, it is noteworthy that BUs with n = 3n′ + 2 are structurally polar from the point of view of their Bi3+ repartition. In the here-observed materials, it yields acentric intergrowths between BUs with a large deviation from centrosymmetry in term of electronic density repartition. The acentric space group was checked by preliminary second-harmonic generation (SHG). The mega-series corresponding to the intergrowths between the same ribbons has been rationalized as a function of n. One third of them should preferentially be acentric materials due to the most stable ferro-arrangement between the polar BUs.