Dc. Sinclair et al., OPTIMIZATION OF SUPERCONDUCTING CRITICAL-TEMPERATURES BY CONTROL OF CATION AND ANION STOICHIOMETRY IN BI2SR2CACU2O-DELTA-BASED SOLID-SOLUTIONS, Journal of Materials Science, 30(11), 1995, pp. 2743-2746
T-c data are reported for powders of cation-stoichiometric Bi2Sr2CaCu2
Odelta and for nonstoichiometric samples based on the three mechanisms
Bi reversible arrow Sr, Sr reversible arrow Ca a nd Sr vacancy. For e
ach, the T-c values depend critically on the final oxygen contents, wh
ich were varied by heating samples in either O-2 or N-2 at different t
emperatures. Stoichiometric Bi2Sr2CaCu2Odelta has the highest T-c, 92
K, obtained after heating in O-2 at similar to 820 degrees C. Heating
in O-2 at lower temperatures gives rise to overdoping and T-c decrease
s to 60 K. The other cation compositions show a smaller maximum T-c bu
t also less reduction in T-c on overdoping. Under-doped samples, with
reduced T-c values were obtained on heating in N-2. These data, togeth
er with selected literature results, lead to a unified picture of the
variation of T-c with cation composition and oxygen content.