Fluorination of La2NiO4 and La2CuO4+δ

We have carried out fluorination on La2NiO4 and La2CuO4+δ. Only a small fraction of fluorine enters the bulk; the rest resides on the surface. The cuprate after fluorination exhibits greater departures from tetragonal symmetry than the parent material and transforms at ∼40 K to the superconducting state. By contrast, the nickelate deviates less from tetragonal symmetry upon fluorination; no superconductivity was observed down to 4.2 K.