ISSN 1062-8738, Bulletin of the Russian Academy of Sciences: Physics, 2007, Vol. 71, No. 8, pp. 1104–1106. © Allerton Press, Inc., 2007. Original Russian Text © L.G. Mamsurova, N.G. Trusevich, N.B. Butko, A.A. Vishnev, 2007, published in Izvestiya Rossiiskoi Akademii Nauk. Seriya Fizicheskaya, 2007, Vol. 71, No. 8, pp. 1139–1141. 1104 The previous X-ray and Mössbauer data [1–3] sug- gest that fine-grained high-temperature superconduc- tors (HTSCs) of the YBa 2 Cu 3 O y type are unique objects in which the carrier density in superconducting planes can be changed not only through variation of the total oxygen content but also as a result of partial oxygen redistribution between different layers of the crystal structure. It was of interest to obtain experimental evi- dences for this suggestion. The YBa 2 Cu 3 O y (y ≈ 6.92, T C ≈ 92 K) samples under study, with micron and submicron average grain sizes, are characterized by a certain type of structural disorder [1, 2] at which, in view of the nonequilibrium synthesis conditions and, in particular, high-speed mechanism of structure formation, only some part of cations occupy equilibrium positions. In some part of unit cells, inter- change between Y 3+ and Ba 2+ cations occurs, which leads to oxygen redistribution. The oxygen content increases in chain CuO δ planes and decreases in super- conducting CuO 2 planes. The smaller the average grain size in a sample, the higher the concentration of dis- torted unit cells and the larger the deviation of the aver- age unit-cell volume 〈V〉 from its equilibrium value for a given y . It is noteworthy that the scale of change in the vol- ume V is nanoscopic, i.e., smaller than such character- istic parameters as the coherence length ξ ab (0) and the magnetic field penetration depth λ ab (0). Hence, the quantity 〈V〉 acquires a certain physical meaning. Its deviation from the equilibrium value characterizes the degree of structural disorder in the same way as the measured parameter δ (determination of the latter was described in detail in [1, 2]). Figure 1 demonstrates the increase in the oxygen δ amount in chain planes and the decrease in the degree of orthorhombic distortion with a deviation of the aver- age unit-cell volume 〈V〉 from the optimal value V opt , which is characteristic of equilibrium samples with Û = 6.92. Figure 1 shows also the values of y and T C for the samples studied; the weak variation in these parameters does not correlate with the changes in 〈V〉. Figure 2 shows the experimental dependences of the temperature-independent contribution χ 0 and the coher- ence length ξ ab (0) (obtained for samples of the same series from the analysis of the magnetic susceptibility of the normal state [4]) and the magnetization å (mea- sured in the field H = 6 kOe at T = 0.9T C ) on 〈V〉. As was shown in [5, 6], the temperature-indepen- dent contribution χ 0 includes several parts: electronic diamagnetism of the atomic core, orbital van Vleck paramagnetism, and spin paramagnetism of conduction electrons. The first two parts are independent of the oxygen content y , they are comparable in magnitude but have opposite signs. As a result, they compensate each other to a great extent (with a slightly superior diamag- netic part). In sum, the experimentally observed value χ 0 consists predominantly of the spin (Pauli) suscepti- bility of conduction electrons, which is determined by the density of states N(0) near the Fermi level: ~ N(0). Figure 2a demonstrates an almost linear dependence of the temperature-independent contribution to χ 0 on 〈V〉 for the samples studied. The value of χ 0 increases with a decrease in 〈V〉. Previously, a similar change in χ 0 was observed for equilibrium YBa 2 Cu 3 O y samples with an increase in the total oxygen content Û [5]. It is known [7] that such an increase in y is accompanied by χ 0 P Effect of the Nanoscale Structural Inhomogeneity on the Magnetic and Superconducting Characteristics of Fine-Grained YBa 2 Cu 3 O y HTSCs L. G. Mamsurova, N. G. Trusevich, N. B. Butko, and A. A. Vishnev Semenov Institute of Chemical Physics, Russian Academy of Sciences, ul. Kosygina 4, Moscow, 119991 Russia e-mail: mamsurova@chph.ras.ru Abstract—It has been experimentally established that the nanoscale structural inhomogeneity, inherent in fine- grained (0.4 ≤ 〈D〉 ≤ 2μ m) high-temperature superconductors YBa 2 Cu 3 O y (y ≈ 6.92, T C ≈ 92 K) and manifesting itself in partial interplane redistribution of oxygen [1, 2], changes the density of states near the Fermi level and decreases the coherence length and density of superconducting carriers in CuO 2 planes. The revealed relation- ship between the changes in these characteristics with respect to their equilibrium values corresponds to the relationship that might occur for conventional superconductors. DOI: 10.3103/S1062873807080163