“…T c , the superconducting phase transition temperature, as a function of oxygen content x is known to display the prominent 60 K and 90 K plateaus for RE = Yb, Y and Er [6], i.e., the compounds of comparatively small RE ionic radii. The analog of the 60 K plateau is less pronounced for RE = Gd [7], and the plateaus are practically absent for the REBCO compounds with RE = Nd [6,7] and La [8]. The distribution of chain lengths in the CF ensemble allows one to estimate the concentration of holes leaving the chains, n h , which is usually assumed to be proportional to T c , unless one is in the underdoping (n h < 0.05) and overdoping (n h > 0.25) regimes.…”