  Superconductivity in the electric field-effect doped infinite layer compound
CaCuO2 is considered. It is argued that in the superconducting CuO2 layer, next
to the insulating Al2O3 overlayer, the coordination of the Cu2+ ions by oxygens
is pyramidal rather than square planar. This view stems from existing NEXAFS
and the analysis of HRETM results, as well as chemical considerations, and is
discussed mainly for the hole doped but also the electron doped region of the
phase diagramm.
