Abstract
Distinct calcium and oxygen doping effects were studied in the ${\mathrm{C}\mathrm{u}(\mathrm{B}\mathrm{a}}_{0.8}{\mathrm{Sr}}_{0.2}{)}_{2}({\mathrm{Yb}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}){\mathrm{Cu}}_{2}{\mathrm{O}}_{6+z}$ $(\mathrm{Cu}\ensuremath{-}1212:P)$ system by means of neutron diffraction and superconducting quantum interference device experiments in the wide substitution ranges of $0l~xl~0.35$ and $0lzl1.$ The effectiveness of the two different ways to introduce holes into the ${\mathrm{CuO}}_{2}$ planes was compared both in respect to the capability to increase ${T}_{c}$ and in terms of the hole production as estimated from neutron-diffraction data via bond-valence-sum calculation. Oxygen doping was found to increase the hole concentration less efficiently, and further, at a certain hole concentration value higher ${T}_{c}$ values were obtained with calcium substitution than with oxygen doping. The two different hole-doping methods exhibited also different ${T}_{c}$ vs Cu-O bond length relations. As a conclusion, the possible roles of the hole distribution in the in-plane Cu-O bond and the flatness of the ${\mathrm{CuO}}_{2}$ planes in determining the superconducting properties were recognized.
Published Version
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