Coulometric determinations of valence of metal ions and oxygen content in YBa_2(Cu_(1-x)T_x)_3O_y (T chemical bounds Fe, Co and Ni)

摘要

Valence of the transition metal ion T and the oxygen content in YBa_2(Cu_(1-x)T_x)_3O_y were determined independently by using the coulometric titration technique for the cases of T chemical bounds Fe, Co and Ni. Here, the Cu ions in the Cu(1) chain site are mainly substituted by Fe and Co ions, while in the Cu(2) plane site by Ni. It was found that the increase of y with increasing x is compensated by increase of positive charge due to the increase of cation composition with larger valence than the of Cu and/or increase of valence of doped cations, resulting that the Cu valence does not change significantly and is almost independent of x, implying that the hole concentration in the sample does not change as a whole. The present results imply that the microscopic hole distribution and/or the localization of the holes in the Cu(1)-O chain and/or in the Cc(2)-O_2 plane due to the T-substitution may play an important role for superconducting properties in this system.