90 K PHASE-FORMATION IN Y-BA-CU-O SYSTEM IN AMBIENT AIR THROUGH MERCURY SUBSTITUTION

In this communication we report the formation of the 90 K superconduct ing phase in a composition Y1Ba2-xHgxCu3O7-delta while the material is sintered in ambient air. A T-c0 (zero resistivity) of 90 K is obtaine d for a value of x = 0.01. Present studies confirm our earlier inferen ce that HgO dissociates (into Hg and O-2) during the reaction, providi ng a high oxygen activity ambient which might change the oxygen balanc e in favour of high Cu-valence state, as well as oxygen stoichiometry favourable to the formation of superconducting phase. Hg escapes the m atrix without influencing crystal structure.