  The aging effects in YBa2Cu3O6+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 t and a detailed experimental dependence of the YBa2Cu3O6+d
lattice parameters a, b, and c on both d and t 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; t) dependence are well described by a
second-order polynomial with applying different coefficients for different t.
The behavior c has been explained on the basis of a simple model of the Coulomb
interaction between the CuO2 and CuOd structural planes, in which the hole
charge transfer from CuOd to CuO2 takes place providing the standard level of
Tc in YBa2Cu3O6+d (this level is characterized by a maximum Tc of 93 K at d =
0.9). It has been demonstrated that the c(d; t) dependence is a good
alternative to assessing the hole concentration in YBa2Cu3O6+d. By analyzing
the c(d; t) experimental dependence as well as the data on the hole
localization in the pairs Cu-O 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 3d9L-1 electron configuration to Cu 3d8
for copper in the basal plane of YBa2Cu3O6+d at RT.
