<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mn>3</mml:mn><mml:mi>d</mml:mi></mml:math>-metal doping of the high-temperature superconducting perovskites La-Sr-Cu-O and Y-Ba-Cu-O

The structural, magnetic, and superconducting properties of the mixed compounds ${\mathrm{La}}_{1.85}{\mathrm{Sr}}_{0.15}{\mathrm{Cu}}_{1\ensuremath{-}x}{M}_{x}{\mathrm{O}}_{4}$ ($0&lt;x&lt;0.3$) ($M=\mathrm{Ni}\mathrm{or}\mathrm{Zn}$) and $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3\ensuremath{-}x}{\mathrm{Ni}}_{x}{\mathrm{O}}_{7\ensuremath{-}y}$ ($x=0.25 or 0.5$) were studied. dc resistance, meissner, and shielding measurements have shown that both magnetic Ni and diamagnetic Zn ions destroy the superconductivity in the La-Sr-Cu-O system. Within the Y-Ba-Cu-O system, the replacement of copper by nickel depresses ${T}_{c}$ from 93 K ($x=0$) to 50 K ($x=0.5$). At higher nickel contents, the phase does not form. The upper critical field ${B}_{c2}(T)$ of the nickel-doped samples was measured near ${T}_{c}$ in dc fields to 23 T. Resistive midpoint transitions yield $\frac{d{B}_{c2}}{\mathrm{dT}}=4.5 \mathrm{and} 1.77$ T/K for the Ni-doped La-Sr-Cu-O ($x=0.025$) and Y-Ba-Cu-O ($x=0.5$) systems, respectively. We compare doping results for magnetic and nonmagnetic ions, and discuss the origin of the depression in ${T}_{c}$.

Not yet translated