Growth and Characterization of Large YBa sub 2 Cu sub 3 O sub 7--x Single Crystals

Centimeter sized crystal plates of YBa sub 2 Cu sub 3 O sub 7--x have been obtained using a bulk composition and method described by Schneemeyer et al. modified for growth in a pure oxygen atmosphere. A porous MgO crucible and long soak time promote large crystals. Magnesium was not detectable in the crystals. Electron microbeam analysis using a 60 A monochromator crystal for the oxygen determination gave the composition: Y sub 1.05 Ba sub 2.02 Cu sub 2.94 O sub 6.52 plus/minus 0.06 . As-grown crystals from the melt surface exhibit a fairly sharp T sub c with zero resistance at 80K, and show complex twinning and crack patterns. Optical micrographs of a lightly polished surface normal to the c-axis of a approx 3 mm crystal delineate twinning and fine scale microcracking; this crystal surface now has a zero resistance at 68K. Microhardness measurements and micro-fracture observations indicate intrinsic properties that may inhibit or impede large scale manufacture of electronic ceramics. 14 ref.--AA