Superconductivity at 55 K in La0.7Sr1.3Cu(O,F)(4+delta) with reduced CuO2 sheets and apical anions

Superconducting copper fluoride La0.7Sr1.3Cu(O,F)(4+delta) with T-c=55 K had been synthesized via the solid phase fluorination of La0.7Sr1.3CuO3.25 with CuF2 at relatively low temperature. The fluoride is a derivative of its precursor, but its lattice constant a is expanded from 3.7547(5) to 3.9368(7) Angstrom, while its lattice parameter c is expanded from 12.896(3) to 13.075(4) Angstrom. The obvious difference in lattice parameters and crystal structure seems to distinguish this compound from the superconducting Sr2CuO2F4+delta reported in a recent study. It gives strong evidence for superconductivity with reduced CuO2 sheets while in the presence of apical oxygen or fluorine.