Europium-based high-temperature superconductors studied by x-ray diffraction and Eu151 Mössbauer spectroscopy

J. Lindén*, J. Hietaniemi, E. Ikonen, M. Lippmaa, I. Tittonen, T. Katila, T. Karlemo, M. Karppinen, L. Niinistö, K. Ullakko

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

15 Citations (Scopus)

Abstract

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.

Original languageEnglish
Pages (from-to)8534-8541
Number of pages8
JournalPhysical Review B
Volume46
Issue number13
DOIs
Publication statusPublished - 1992
MoE publication typeA1 Journal article-refereed

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