Evolution structurale et proprietes physiques des phases AXMO2 (A = Na, K; M = Cr, Mn, Co) (x ⩽ 1)

The structures of the AXMO2 (x ⩽ 1) phases may be classified in three main groups. The layer structures are the most common, their anionic packing varies with the nature of the alkali element and its insertion rate. The tunnel structures are observed only for manganese and small values of x. Cristobalite derived structures characterize the KMO2 oxides for small size M3+ cations. Whereas the AxCrO2 and AxMnO2 phases are semi-conductors, the AxCoO2 oxides have a metallic behaviour, the small Co-Co distances allowing t2g orbital overlaping through the common edges of adjacent octahedra. The influence of the structure on magnetic properties is discussed.