3d-metal doping of the high-temperature superconducting perovskites La-Sr-Cu-O and Y-Ba-Cu-O

Abstract

The structural, magnetic, and superconducting properties of the mixed compounds ${\mathrm{La}}_{1.85}{\mathrm{Sr}}_{0.15}{\mathrm{Cu}}_{1-x}{M}_x{\mathrm{O}}_4$ ($0<x<\mathrm{}0.3\mathrm{}$) ($M=\mathrm{Ni}\mathrm{or}\mathrm{Zn}$) and $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_{3-x}{\mathrm{Ni}}_x{\mathrm{O}}_{7-y}$ ($x=0.25\mathrm{} or 0.5$) 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 ($x=0\mathrm{}$) to 50 K ($x=0.5\mathrm{}$). At higher nickel contents, the phase does not form. The upper critical field $B_{c2\mathrm{}}\mathrm{}\left(T\right)\mathrm{}$ of the nickel-doped samples was measured near $T_c$ in dc fields to 23 T. Resistive midpoint transitions yield $\frac{d{B}_{c2\mathrm{}}}{\mathrm{dT}}=4.5\mathrm{} \mathrm{and} 1.77$ T/K for the Ni-doped La-Sr-Cu-O ($x=0.025\mathrm{}$) and Y-Ba-Cu-O ($x=0.5\mathrm{}$) systems, respectively. We compare doping results for magnetic and nonmagnetic ions, and discuss the origin of the depression in $T_c$.