Original positively charged nanoflakes by liquid exfoliation of layered oxybromide cobaltites

Abstract

For the synthesis of novel positively charged 2D-elementary blocks, we have focused on the exfoliation of recent mixed valent Co^3+/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 (∼100 nm large and ∼10 nm thick) where the Co^3+/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.