Synthesis and structure of the calcium copper oxyfluoride, Ca2CuO2F2+δ
Abstract
The synthesis of the copper oxyfluoride, Ca2CuO2F2+δ, by reaction of Ca2CuO3 with elemental F2 at low temperatures (240 °C) is reported. Preliminary structure refinement of powder neutron diffraction data suggests that Ca2CuO2F2+δ is structurally related to Nd2CuO4, rather than to the La2CuO4 structure observed for the related copper oxyfluoride, Sr2CuO2F2+δ. 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 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 has so far been found in this phase down to 4 K.
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