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Structural and microstructural features of functional materials based on cuprates and manganites

“…1] should be pointed out. This component is characteristic 119,127 only of annealed samples of the Nd213 : Fe solid solution with superstructural ordering of neodymium and barium atoms.…”

“…4 are convenient for establishment of correspondence between parameters of MoÈ ssbauer spectra and particular types of coordination polyhedra of the iron atoms occupying positions of copper atoms. 119,120 With heterovalent substitution of neodymium for barium the isomer shifts of the corresponding components increase (see Fig. 4) owing to stabilisation of the Fe 3+ ions occupying the Cu1 positions in the substitutional solid solutions characterised by charge transfer between the dielectric block and the superconducting planes.…”

“…116 ± 120 These components originate from replacement of neodymium atoms by barium atoms. 118,119 The Fe(IV) Cu1 O 6 octahedra are distorted owing to asymmetry of the second coordination sphere comprised of Ba atoms occupying their proper positions and Nd atoms occupying positions of Ba atoms. An increase in the formal oxidation state of iron atoms (decrease in isomer shift) can be explained by the formation of an associate of defects, Fe(IV) Cu1 O 6 7Nd Ba (Fig.…”

Thermal instability of a cation-disordered NdBa2Cu3O7 superconductor

“…A special two-step procedure was used to prepare pseudocubic Nd123 samples. [6][7][8] The first stage consisted in the preliminary annealing of 5 mm pellets of the oxide precursor at 750 °C for 15-70 h in air. The second step was re-grinding, pressing and short-term (2-5 h) annealing at 950-1000 °C on MgO plates in air followed by quenching in liquid nitrogen.…”

“…This is a sign of cation re-distribution within a crystal lattice, as we detected earlier by EXAFS, XRD and Raman scattering spectroscopy. 4,[6][7][8] An intermediate low-temperature treatment may predetermine a low T c in Nd123 samples, especially for chemically homogenised submicron-particle precursors. The two-stage treatment described above allowed us to obtain for the first time intentionally and reproducibly pseudocubic neodimium-barium cuprates with the 1:2:3 stoichiometry.…”