Effects of Oxygen Stoichiometry on Superconducting Properties of the Ceramics ABa2Cu3O7-δ, With A = Yb, Y, Gd and La

From microscopic description to statistical mechanics of CuO chain fragments in high-Tc superconductors REBa2Cu3O6+x

“…In that figure, we also included Monte Carlo data for µ = 1.56, mimicing a REBCO compound where the rare earth ions would be even smaller than yttrium, like YbBCO (see table I). Indeed, it was shown experimentally [6] that the 60 K plateau in YbBCO is even more manifest than in YBCO, in accordance with the MC data.…”

“…µ = 1.59, 1.62 and 1.66. One readily sees, in accordance with the experiments, that the low-temperature plateau in T c versus x is expected to be much less pronounced in NdBCO [7,6] and absent in LaBCO [8]. In that figure, we also included Monte Carlo data for µ = 1.56, mimicing a REBCO compound where the rare earth ions would be even smaller than yttrium, like YbBCO (see table I).…”

“…For example, Cu (5) would appear, if an oxygen atom formed a 90 • configuration with two other oxygen atoms (all three are supposed to be adjacent to the same Cu atom). The energy loss due to a Cu (5) (Cu (6) ) ion would be 2V 1 (4V 1 ). From the simulations, the concentration of such ions is seen to be very small for all oxygen contents x.…”

“…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].…”

“…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.…”