X-ray identification of the superconducting high-Tcphase in the Y-Ba-Cu-O system

The phase responsible for superconductivity above 90 K in the Y-Ba-Cu-O system has been tentatively identified as the ${\mathrm{La}}_{3\mathrm{-}\mathrm{x}}$ ${\mathrm{Ba}}_{3+\mathrm{x}}$ ${\mathrm{Cu}}_6$ ${\mathrm{O}}_{14+\mathrm{y}}$-type structure through a combination of x-ray diffraction and superconducting transport measurements.