Enhancement of Tc of CyCu1-yBa2Ca2Cu3O x from 61 K to 120 K by reduction treatments

CHAILLOUT, C.; LE FLOCH, S.; GAUTIER, E.; BORDET, P.; ACHA, C.; FENG, Y.; SULPICE, A.; THOLENCE, J.L.; MAREZIO, M.

PHYSICA C - SUPERCONDUTIVITY

ELSEVIER SCIENCE BV

Año: 1996 vol. 266 p. 215 - 222

0921-4534

The Tc of the CyCu1-yBa2Ca2Cu3O 8+δ (y ≈ 0.5) phase, synthesized under high pressure, has been raised from 67 K to about 120 K by heat-treatments under reducing conditions. An increase of both a and c lattice parameters occurs concomitantly with that of Tc (before: a = 3.858 (1), c = 14.766 (9) Å, after: a ≈ 3.862(1), c ≈ 14.825 (3) Å). Subsequent heat-treatments under oxygen atmosphere lead, reversibly, to a decrease of Tc and of the lattice parameters. Consequently, the increase of Tc has been associated with an oxygen loss. Measurements of the resistivity under high pressure indicate that after reduction the overdoped as-prepared samples go towards the optimal doping. A structural model is proposed about the position of the mobile oxygen in the basal plane of the structure.