Effect of Ga addition to Y${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$

The effect of Ga substitution for Cu in $\mathrm{Y}{\mathrm{Ba}}_2{\left({\mathrm{Cu}}_{1-x}{\mathrm{Ga}}_x\right)}_3{\mathrm{O}}_y$ has been investigated for nominal compositions $x\le 0.10$. Samples are tetragonal for $x>\mathrm{}0.03\mathrm{}$. For $x\ge 0.05$, evidence for second phase appears in x-ray-diffraction diagrams. Superconducting transition temperature $T_c$ falls systematically with increasing $x$. The systematic variations in $T_c$ and lattice parameters with nominal $x$ suggest that Ga solid solution may extend to $x=0.05\mathrm{}$. However, electron microprobe results indicate that Ga incorporation into the superconducting phase is extremely limited; the Ga content $x$ of the superconducting phase appears to be $x\le 0.01$. A Ga-rich second phase is also observed by microprobe for $0.01\le x\le 0.10$.