Oxygen ordering and the 60 K plateau in the ortho-II phase of YBa2Cu3O6+x (0.48≤x≤0.62)

The dependence of critical temperature on oxygen concentration in YBa2Cu3O6+x in terms of the fragmented chain model

“…2 it also follows that if is set to be < 3 the ( ) function will be monotonically increasing over the 60 K plateau (OII phase), while for > 3 it will decrease. It should be noted that although some earlier experimental results have pointed to the T ( ) dependence as being strictly constant in the regime of the 60 K phase [5,7] (implying that both ( ) and ( ) functions are constant as well), a recent experimental study indicated that the 60 K plateau of T ( ) is not exactly a strictly horizontal plateau, but rather a sort of "quasi plateau", so that T ( ) in fact increases monotonically, though at a slow rate, over the regime of the plateau [9]. With this in mind we therefore used = 2 (< 3) to be inserted into (1) (i.e.…”

“…The problem of oxygen ordering in the oxygen deficient CuO (basal) planes and its influence on doping (number of holes per one Cu(2) ion) of the superconducting CuO 2 layers, and thus on the superconducting properties of the high-T YBa 2 Cu 3 O 6+ material, has been extensively studied for more than two decades [1][2][3][4][5][6]. By now it has been widely accepted that not only the variable oxy-gen concentration , but also the degree of oxygen order in CuO planes, controls the crystallographic structure as well as the electronic properties of the system, leading to an insulating antiferromagnetic state for approximately < 0 4, while for > 0 4 the material starts becoming a superconductor.…”

“…While the formation of the 90 K plateau is explained in terms of optimal doping of CuO 2 planes [15], appearance of the 60 K plateau is still the subject of scientific debates [6,16]. The first theories, that were suggested in order to account for the emergence of the 60 K plateau, associated this plateau with the formation of the Ortho II structural phase (characterized by long CuO chains) and peculiarities of the accompanying charge transfer [5,16], while some later theories involved other mechanisms [6,15,17].…”

Mechanical and Transport Properties of Argon Annealed Y1 − x Ca x :123 Superconductors

“…However, the different behavior of (ssqHpAr, sssLpAr) and (sssHpAr, ssqLpAr) samples, resulting from Ar heat treatment, may be indicative of an oxygen loss mechanism operating differently in the two different series. It is well known that Ar heat treatment on the pure Y:123 system leads to removal of oxygen from the CuO chains to the environment [10,18,19]. In the case of ssqHpAr and sssLpAr samples, the oxygen is removed from CuO chains, partially fills some of the existing oxygen vacancies in the CuO 2 planes, and is partially lost to the environment.…”

“…It is well known that Y: 123 oxygenated superconducting systems can lose oxygen from their Cu-O chains by argon heat treatment at a temperature of 450 • C for 12 h, and consequently the oxygen content of Y: 123 is decreased from 7 towards 6 along with a gradual decrease in T c [10], while the Cu-O 2 planes are supposed to stay unaffected by such Ar heat treatment. In contrast, Y 1 − x Ca x :123 superconducting samples have shown two different mechanisms of oxygen transfer through Ar heat treatment, and T c could be improved [11].…”