Effect on superconductivity of high valence ions V4+ and Ni3+ substitution for Cu site in Pr1.85Ce0.15CuO4−δ system

Effects of high valence ions V4+ and Ni3+ substitution on superconductivity are studied systematically for the electron-doped superconducting Pr1.85Ce0.15CuO4−δ (PCCO) system. The results indicate that very small amount of V4+ substitution (x ⩽ 0.04) for Cu2+ site improves the superconductivity, but further substitution (x ⩾ 0.06) will depress the superconductivity. Contrasting with V4+, Ni3+ substitution shows a strong suppression on superconductivity, even for extremely small amount substitution of 0.01. Both the change of lattice parameters and the similar 3d electron structure of V4+ ion to the Cu2+ ion support the improvement of superconductivity while x ⩽ 0.04 in the V-substituted PCCO system. The results of Hall effect indicate that high valence ion substitution for Cu2+ increase the carrier concentration, which is also one reason for the improvement of superconductivity of V4+ substitution PCCO.