Original positively charged nanoflakes by liquid exfoliation of layered oxybromide cobaltites
Résumé
For the synthesis of novel positively charged 2D-elementary blocks, we have focused on the exfoliation of recent mixed valent Co3+/4+ oxy-bromides, namely the 14H-Ba7Co6BrO17 and 18R-Ba6Co5BrO14 phases built on hexagonal-perovskite blocks separated by [Ba2O2Br](-)spacers. Here, we show that the exfoliation in butanol leads to positive nanoblocks in colloidal suspensions, as confirmed Zetametry measurements. Full structural characterization was performed by TEM, EDS, Raman and IR spectroscopies, AFM, X-ray absorption spectroscopy (XANES and DANES) and synchrotron X-ray diffraction (in-plane and out of plane). Combination of all these techniques results into a detailed description of crystalline flat particles (similar to 100 nm large and similar to 10 nm thick) where the Co3+/4+ mixed oxidation state, as well as the local Co environment, are preserved after the exfoliation process. In-plane and out of plane synchrotron X-ray diffraction confirms a strong preferred deposition (001) planes. The original bulk materials showing intrinsic ferromagnetism in the elementary blocks, the magnetic properties of the delaminated nanoparticles are also presented here. Finally, we have prepared new positive nanometric bricks based on hexagonal perovskite structure, rare objects in condensed matter.