Superconductivity has been observed in originally semiconducting ceramic samples of ${\mathrm{La}}_2$${\mathrm{CuO}}_4$ following oxidation in an electrochemical cell at room temperature. After processing, the room-temperature resistivity is lowered by over an order of magnitude and, on cooling below 150 K, acquires a metallic temperature dependence. The superconducting transition occurs near 45 K. Magnetic-susceptibility measurements confirm the bulk nature of the superconductivity. Furthermore, by reversing the polarization of the cell, semiconducting ${\mathrm{La}}_2$${\mathrm{CuO}}_4$ can again be produced. The homogeneity of the processed samples was verified by x-ray powder diffraction and energy-dispersive x-ray elemental analysis.

• Received 27 February 1991

DOI:https://doi.org/10.1103/PhysRevB.44.2727