SYNTHESIS AND CHARACTERIZATION OF SUPERCONDUCTING YBBA2CU3O7-DELTA AND Y1-XLUXBA2CU3O7-DELTA (0.0 LESS-THAN X LESS-THAN 0.75) - LOWER LIMIT OF THE RARE-EARTH ION RADIUS TOLERATED IN THE 123-CUPRATE SYSTEM

YbBa2Cu3O7-δ with a Tc (zero-resistance) of 89K has been prepared without contamination of Yb2BaCuO5. Monophasic LuBa2Cu3O7-δ cannot be prepared. Solid solutions of the type Y1 xLuxBa2Cu3O7-δ (0.0 < x ≤ 0.75) are, however, stable and superconducting (zeroresistance Tc, 89K). It appears that the lower limit of the rare earth ion radius tolerated by the 123 cuprate structure is close to that of Yb3+ (0.985 Å). © 1990.