Tc of overdoped YLa0.2Ba1.8Cu3O7.06+y and La1.2Ba1.8Cu3O7.2+y

Heat treatment of YLa0.2Ba1.8Cu3O7.06 at high oxygen pressure produces overdoped YLa0.2Ba1.8Cu3O7.06+y (y ≤ 0.7). Likewise, such treatment of La1.2Ba1.8Cu3O7.2 produces overdoped La1.2Ba1.8Cu3O7.2+y (y ≤ 0.8). With increasing y, Tc of the former rises from 50 K (y=0) to 90 K (y=0.3), then fluctuates somewhat between 87 and 90 K up to y=0.7. In the case of the latter, although Tc remains unchanged at 27 K with increase in y up to ∼0.2, the volume fraction of superconductivity is reduced to zero at y=0.2. (author)