Synthesis and structure of the calcium copper oxyfluoride, Ca2CuO2F2+δ

Calcium copper oxyfluoride was synthesised by reaction of Ca2CuO3 with elemental F2 at low temperatures (240 C). Preliminary structure refinement of powder neutron diffraction data suggests that calcium copper oxyfluoride is structurally related to Nd2CuO4, rather than to the La2CuO4 structure observed for the related strontium copper oxyfluoride. The change in structure type is attributed to a decrease in size of the alkaline-earth cation. Madelung energy calculations support the view that fluorine insertion causes O/F interchange to give CuO2 planes with the fluorine atoms located between the Ca bilayers. Although the structure could potentially support superconductivity, no evidence for superconductivity was found in this phase down to 4 K. 13 refs.