Valence State of Cu in Nd_2-xCe_xCuO₄ System

Abstract

We present XPS studies of semiconducting Nd 2- x Ce x CuO 4 (0≦ x ≦0.20) and superconducting Nd 1.85 Ce 0.15 CuO 4- y to clarify the location of the electron carriers. Examination of the Ce3 d spectra shows that the Ce ions are donors of electron carriers. From the analysis of the Cu2 p spectra, the Cu + concentration is found to increase with the Ce concentration x . A definite increase in the Cu + concentration due to the reduction procedure is found for the superconducting sample. The present results suggest that the conduction of the electron carriers takes place in the CuO 4 square plane in this system.