Oxides RBa2Cu3O6+δ(R=Y, Nd) subjected to mechanical activation in AGO-2 mill have been studied by X-ray photoelectron spectroscopy (XPS), thermal analysis, and magnetometry. It has been shown that mechanoactivation accelerates chemical degradation under the impact of H2O and CO2in YBa2Cu3O6+δsamples. Degradation occurs in the standard way. Investigation of mechanically activated NdBa2Cu3O6+δhas revealed other results. It has been suggested that CO2can diffuse into its structure more freely than in YBa2Cu3O6+δ; as a result, carbonization may proceed directly in the volume of NdBa2Cu3O6+δand independently of the hydrolysis process. In addition, the mechanism of interaction between the oxide and water is not active and not “traditional” for the homologous series REBa2Cu3O6+δ(where RE = rare earth and Y)—the characteristic “color” phase (Nd2BaCuO5) is not formed during hydrolysis. It is known that high-temperature treatment of NdBa2Cu3O6+δoxide results in partial substitution of cations Ba by Nd; which is accompanied by decrease in the superconducting transition temperature and formation of the impurity phase Ba2Cu3O5+y. According to our data, mechanical activation of the resulting solid solution Nd1+xBa2−xCu3O6+δunexpectedly has led to the reverse redistribution of cations, which has been manifested in the complete disappearance of the impurity phase and increase inTc.

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.

A generalization of expressions for the anisotropic exchange interaction is developed forPaCCMi3TpkiBaeTCII 0606we~kie BbIBOAa AJIH aHki30TpOn~Or0 06MeHHOr0 B~~H M O -AetCTBHH AJXH WY ¶aH HepaBHbIX CnHHOB B OCHOBHOM ki BOa6yM~eHHbIX COCTOHHUIIX. the case of nonequal spins of separate ions for the ground and excited states.

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