Large and high-quality single-crystal growth of cuprate superconductor Bi-2223 using the traveling-solvent floating-zone (TSFZ) method*

In high superconducting transition temperature (high-$T_{\mathrm{c}})$ cuprates, it is empirically known that $T_{\mathrm{c}}$ increases on increasing the number of CuO$_{\mathrm{2}}$ planes in a unit cell n from 1 to 3. Bi-family cuprates are ideal for investigating the microscopic mechanism involved. However, it is difficult to grow tri-layered Bi-2223, probably owing to its narrow crystallization field. Here, we report improved crystal growth of this compound using the TSFZ method under conditions slightly different from those in an earlier report [J. Cryst. Growth 223, 175 (2001)]. A Bi-rich feed-rod composition of Bi$_{\mathrm{2.2}}$Sr$_{\mathrm{1.9}}$Ca$_{\mathrm{2}}$Cu$_{\mathrm{3}}$O$_{\mathrm{y}}$ and a slightly oxygen-reduced atmosphere (mixed gas flow of O$_{\mathrm{2}}$ (10{\%}) and Ar (90{\%})) were adopted for the crystal growth. In addition, to increase the supersaturation of the melts, we applied a large temperature gradient along the solid-liquid interface by shielding a high-angle light beam using Al foil around the quartz tube. In this way, we succeeded in preparing large ($2\times 2\times 0.05$mm$^{\mathrm{3}})$ and high-quality (almost 100{\%} pure) Bi-2223 single crystals.