Oxidation state of copper in optimally oxygen-doped 1:2:3 Ca-La-Ba-Cu-O superconductors

Abstract

This paper describes an investigation of the family ``CLBLCO'' of 1-2-3 superconductors CLBLCO $[({\mathrm{Ca}}_{x}{\mathrm{La}}_{1\ensuremath{-}x})({\mathrm{Ba}}_{c\ensuremath{-}x}{\mathrm{La}}_{2\ensuremath{-}c+x})({\mathrm{Cu}}_{1\ensuremath{-}z}{M}_{z}{)}_{3}{\mathrm{O}}_{y}],$ with values $x=0.1,$ 0.2, 0.3, and 0.4, $c=2.00,$ 1.75, and 1.55. The impurity M substituting for Cu was one of Zn, Ni, Co, and Ga, and the value of z was taken from zero to 0.1. Although the maximal value of the transition temperature ${T}_{c}$ occurs at different values of the oxygen content y, the average oxidation state of copper for maximal ${T}_{c}$ is found to be approximately constant. The data for Ni-doped CLBLCO suggest that the oxidation state of Ni in this system appears to be 3.