Equilibrium of 1:2:3 CLBLCO superconductors with oxygen: effect of cooling upon the oxygen content and the homogeneity of its distribution Original Research Article

Liquid nitrogen, liquid oxygen and liquid argon were tested as coolers for quenching performed after equilibrium of (CaxLa1−x)(Ba1.75−xLa0.25+x)Cu3Oy (x=0.1 or 0.4) with oxygen has been attained. This compound has been previously denoted as CLBLCO, CLBCO or CaLaBaCuO. Absorption of O2 during quenching in liquid oxygen was found and measured. Such samples are oxygen inhomogeneous. The transition to superconductivity is wide and begins 20 K higher than for a homogeneous sample having the same oxygen content. Liquid nitrogen, which is usually used as an external cooling agent containing 2–3% of oxygen, also leads to notable oxygen absorption. Only quenching in oxygen free liquid argon or in oxygen free liquid nitrogen does not cause oxygen absorption and may be used for the preparation of homogeneous samples of CLBLCO after equilibration at any temperature in the range from 300 to 950 °C.