On the room-temperature aging effects in YBa 2 Cu 3 O 6+δ

Abstract

a b s t r a c tThe aging effects in YBa 2 Cu 3 O 6+d have been investigated on the low-speed quenched samples in contrast to other similar studies where the high-speed quenched samples were examined. In the framework of the investigation, XPS analysis has been conducted for the samples stored after quenching for the specified times s and a detailed experimental dependence of the YBa 2 Cu 3 O 6+d lattice parameters a, b, and c on both d and s has been obtained. The regime of low-speed quenching results in a threefold increase in the aging effect magnitude. Particular cases of the c(d; s) dependence are well described by a second-order polynomial with applying different coefficients for different s. The behavior c has been explained on the basis of a simple model of the Coulomb interaction between the CuO 2 and CuO d structural planes, in which the hole charge transfer from CuO d to CuO 2 takes place providing the standard level of T c in YBa 2 Cu 3 O 6+d (this level is characterized by a maximum T c of 93 K at d = 0.9). It has been demonstrated that the c(d; s) dependence is a good alternative to assessing the hole concentration in YBa 2 Cu 3 O 6+d . By analyzing the c(d; s) experimental dependence as well as the data on the hole localization in the pairs CuAO obtained by XPS, the authors have made a conclusion about the nature of observed aging effects. The latter are likely to be related to the transition of the Cu 3d 9 L À1 electron configuration to Cu 3d 8 for copper in the basal plane of YBa 2 Cu 3 O 6+d at RT.

Distance to Massive Metal Body—a Paradoxical Parameter that Regulates the Intensity of the Hydration of YBa2Cu3O6.75

“…One can state that the YBCO phase is rather contracted after exposure to air. The lattice parameters of exposed YBCO correspond to the maximally oxidized state of YBCO [9]. On the other hand, our study has not revealed radical changes in the structure that would be evidence of the transformation of YBCO under the action of absorbed water into the pseudo-YBa 2 Cu 4 O 8 phase, as had been observed in [10], or into another phase.…”

Relationship Between Electronic and Crystal Structure in Nd 1 + x Ba 2 − x Cu 3 O 6 + δ

“…phases, occurring in Nd-123ss at   6.6 [13]. Meanwhile, the  dependence of these parameters is rather weak compared to the same dependence of c. It corroborates the result of [4] on the influence of charge in the CuO 2 planes namely on the distance between structural layers, that is reflected in equation (1).…”

“…To obtain samples with different oxygen content, additional annealing in air at temperatures of the range 470-940C following by quenching was conducted. More detailed information on this procedure is contained in [4]. The oxygen content was monitored by the change in mass of the sample during additional 1 h -oxidation at 470 C in air, counting on this treating to give rise to (6+) = 6.953 [13].…”

“…(or its modification given below) with accounting for the charge carriers concentration in the CuO 2 planes to be a linear rising function of [4]. As we can see inFig.…”

“…Hence, in the case of application of the model to other members of the RBa 2 Cu 3 O 6+ family, coefficient A has to vary around the value of 0.345, reflecting uncertainty in parameter  33 estimates. According to [4], the change in coefficient A with  is negligible.…”