Europium-based high-temperature superconductors studied by x-ray diffraction and 151Eu Mössbauer spectroscopy

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School of Chemical Technology | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
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Physical Review B, Volume 46, Issue 13
Isotropic powders and magnetically aligned crystallites of EuBa2Cu3O7−δ (1:2:3) and europium-doped Bi2Sr2CaCu2O8 (2:2:1:2) were studied by means of x-ray diffraction and Eu151 Mössbauer spectroscopy. The degree of crystallite orientation of the samples and the values of the lattice constants were determined by x-ray diffraction. The Mössbauer spectra were analyzed considering the full hyperfine Hamiltonian of the nuclear states of the 21.5-keV γ transition. The Mössbauer hyperfine parameters obtained from the superconducting and semiconducting phases are presented. A small change is seen in the Eu151 isomer shift when the oxygen deficiency δ of the 1:2:3 compound is varied. The shift can be explained by a decrease in the s-electron density due to lattice expansion. The changes in the oxidation state of the copper atoms with varying δ were determined from the Mössbauer data: The Cu(2) atoms retain their oxidation state, whereas the Cu(1) atoms adjust their valence according to the value of δ. In the 2:2:1:2 samples, the Eu concentration clearly affected the value of the electric-field gradient at the Eu nucleus. Using a standard procedure, magnetically aligned 2:2:1:2 samples were prepared. The preferred direction of the crystal c axis changed from parallel to perpendicular alignment with the external magnetic field, when the Eu concentration exceeded 20% of the Ca atoms.
Mössbauer spectroscopy, superconductors, europium
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Lindén, J. & Hietaniemi, J. & Ikonen, E. & Lippmaa, M. & Tittonen, I. & Katila, T. & Karlemo, T. & Karppinen, Maarit & Niinistö, L. & Ullakko, K. 1992. Europium-based high-temperature superconductors studied by x-ray diffraction and 151Eu Mössbauer spectroscopy. Physical Review B. Volume 46, Issue 13. 8534-8541. ISSN 1550-235X (electronic). DOI: 10.1103/physrevb.46.8534.