Superconductivity of Nd_1.85Ce_0.15CuO_4-y by Electrochemical Oxidation

Superconductivity of n-type superconductor Nd_1.85Ce_0.15CuO_4-y(NCCO) by electrochemical oxidation is reported for the first time and the cyclic voltammogram curve for NCCO as working electrode is presented. Investifations indicate that after oxidation, superconductivity of NCCO is improved: T_c is raised from 20K up to 26K, the superconducting volume fraction is increased also. The valence electronic states of oxygen and copper in NCCO are studied by x-ray photoelectron spectroscopy. It is found that the Cu-2p_3/2 peak shifts to the higher binding energy side about 0.4eV, which indicates that the valence-state of copper ions is risen up after oxidation. These results imply that hole-carriers exist in n-type superconductor.