Increase of Tc in the 1:2:3 superconductors YBCO and (CaxLa1−x)(LauBa1−u)2Cu3Oy after slow cooling or low temperature annealing

The well known phenomenon of the increase of Tc of YBCO after slow cooling or low temperature annealing without change of the oxygen content, was found also for the YBCO like tetragonal superconductors of (CaxLa1−x)(LauBa1−u)2Cu3Oy (this compound has been previously denoted as CLBLCO, CLBCO or CaLaBaCuO). It has been observed at 150 and 100 °C for oxygen underdoped, optimally- and overdoped ceramics. The products retain their tetragonal unit cells. The possible reasons of this phenomenon are discussed.