SYNTHESIS AND STRUCTURE OF THE CALCIUM COPPER OXYFLUORIDE, CA2CUO2F2+DELTA

The synthesis of the copper oxyfluoride, Ca2CuO2F2+delta, by reaction of Ca2CuO3 with elemental F-2 at low temperatures (240 degrees C) is r eported. Preliminary structure refinement of powder neutron diffractio n data suggests that Ca2CuO2F2+delta is structurally related to Nd2CuO 4, rather than to the La2CuO4 structure observed for the related coppe r oxyfluoride, Sr2CuO2F2+delta. The proposed change in structure type is attributed to the decrease in the size of the alkaline-earth cation . Madelung energy calculations support the view that fluorine insertio n causes O/F interchange to give CuO2 planes with the fluorine atoms l ocated between the Ca bilayers. Although the structure could potential ly support superconductivity, no evidence for superconductivity has so far been found in this phase down to 4 K.