On the problem of holes and electrons in Ce-doped Nd2CuO4

A new approach to the mechanism of Ce/Nd substitution in Nd2CuO4 is proposed. The approach is based on an assumption that the substitution does not involve an appropriate decrease of the oxidation state of the Cu-ions, but proceeds through an exchange of equivalent valences of Nd and Ce, rather than of equal atomic fractions of these elements. The outlined idea is experimentally verified by ac-magnetic susceptibility measurements of a few single-phase test samples. The results obtained allow the case of Ce-doped solid solution of the Nd2CuO4 phase to be treated as a hole-type superconductor, or as a two-band electron-hole type superconductor