Exchange interactions and the state of iron atoms in Bi3Nb1−xFexO7−δ

• Published in: Journal of solid state chemistry Vol. 247; pp. 8 - 12
• Main Authors: Chezhina, N.V., Korolev, D.A., Zhuk, N.A., Lutoev, V.P., Makeev, B.A.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.03.2017
• Subjects: Bismuth niobate; ESR; Magnetic susceptibility; Phase transition; Superexchange; Bismuth niobate; Superexchange; ESR; Phase transition; Magnetic susceptibility
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/j.jssc.2016.12.019

On the basis of the results of magnetic susceptibility and ESR studies of the Bi3Nb1−xFexO7−δ solid solutions iron atoms in the solid solutions of cubic modification of bismuth niobate were found to exist as Fe(III) monomers and exchange bound Fe(III)-O-Fe(III) dimers with antiferro- and ferromagnetic type of superexchange. The exchange parameters and the distribution of monomers and dimers in the solid solutions were calculated as a function of paramagnetic atom content. The study of the Bi3Nb1−xFexO7−δ solid solutions showed that the introduction of iron atoms into the structure of Bi3NbO7 stabilizes the cubic structure of bismuth niobate making the phase transition tetragonal ↔ cubic structure irreversible. In the Bi3Nb1−xFexO7−δ solid solutions we observe the formation of dimers with antiferro- and ferromagnetic exchange. Such clusters are partially retained even at the infinite dilution of the solid solution, which testifies for their rigidity. A sufficiently high parameter of ferromagnetic exchange in a dimer (+53cm−1) seems to result from iron atoms being located in the vicinity of oxygen vacancy. [Display omitted] •The reversible transition cubic – tetragonal modifications in Bi3NbO7 becomes irreversible.•Only cubic modification of Bi3Nb1-xFexO7-δ is stable due to clusters of Fe atoms.•These clusters are sufficiently strong and retained even at the infinite dilution.•The calculations of magnetic susceptibility give the distribution of the clusters and single atoms.