Structure and Magnetism of New Cobalt Oxides and Oxy-halides

Cobalt-oxide based materials has attracted considerable interest in the last decade because of spectacular properties similar to those of the manganites and cuprates. In that field, our investigation of the Ba-Co-X (X =O, F, Cl, Br) systems has led to a number of new mixed-valent CoII/CoIII or CoIII/CoIV materials that has turned out to display complex physical properties1-3. Here, we present brand new results about their crystallographic characteristics (atomic/magnetic structures), their characterizations/physical properties and theoretical calculations by DFT. From the structural point of view, most of the isolated compounds can be deduced of each other by the reorganization of structural blocks isolated by anionic layers. It led to the rational prediction and formulation of the prepared materials using models available in the large family of hexagonal perovskites. As an example, the figure 1 shows the modification of the 5H- and 12H- BaCo3-Δ forms through the replacement of one [BaO2] layers by a [BaOX] layer (X=F, Cl). As we will show, further disconnections of the frameworks can be obtained using [Ba2O2X2] double layers while some common motifs have been evidenced in new Ba/Co oxides