Dielectric properties, Mössbauer study, ESR spectra of Bi2FeTa2O9.5 with pyrochlore structure

• Published in: Journal of alloys and compounds Vol. 903; p. 163928
• Main Authors: Zhuk, N.A., Sekushin, N.A., Semenov, V.G., Fedorova, A.V., Selyutin, A.A., Krzhizhanovskaya, M.G., Lutoev, V.P., Makeev, B.A., Kharton, V.V., Sivkov, D.N., Shpynova, A.D.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 15.05.2022; Elsevier BV
• Subjects: Dielectric loss; Dielectric loss tangent; Dielectric properties; Electrical properties; Electron paramagnetic resonance; Electron spin; Electron states; ESR; Ferric ions; Frequency ranges; Iron; Iron doping; Line spectra; Mossbauer spectroscopy; Mössbauer spectroscopy; Permittivity; Pyrochlore; Pyrochlores; Solid phase synthesis; Spectrum analysis; Spin resonance; Pyrochlore; Iron doping; Dielectric loss tangent; ESR; Permittivity; Mössbauer spectroscopy
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2022.163928

•Bi2FeTa2O9.5 were synthesized by the solid-phase reaction method.•In the Bi2FeTa2O9.5 ESR spectra a dipolar-broadened line (g⁓2.05) from Fe3+ ion clusters are observed.•The Mössbauer spectrum of Bi2FeTa2O9.5 demonstrates a slightly asymmetric doublet.•The doublet is reproduced by a superposition of a doublet (IS = 0.365 mm/s, QS = 0.604 mm/s) and a singlet IS=0.175 mm/s.•The permittivity and the dielectric loss tangent at 20 °C of Bi2FeTa2O9.5 were determined and are 57 and 0.003 (1 MHz). The pyrochlore with the composition Bi2FeTa2O9.5 was obtained by solid-phase synthesis. The electronic state and the nature of the local environment of iron atoms were studied by electron spin resonance (ESR) and Mössbauer spectroscopy. In the Bi2FeTa2O9.5 ESR spectra a dipolar-broadened line with g ∼ 2.05 from Fe3+ ion clusters are observed. This line is the superposition of components with widths of about 150 and 400 mT. On the low-field wing of the band, there is a feature with g ∼ 4.3 relating to trace amounts of isolated Fe3+ ions in an octahedral position with a strong rhombic distortion. The Mössbauer spectrum of the Bi2FeTa2O9.5 compound demonstrates a slightly asymmetric doublet. The form of the doublet is reproduced by a superposition of a doublet and a singlet. About 93% of the spectral area of the paramagnetic part of the spectrum falls on the Fe(III)-doublet with IS = 0.365 ± 0.0020 mm/s, QS = 0.604 ± 0.034 mm/s, correlated with Fe3+ ions in regular axial octahedral positions. The remaining part is represented by a Fe(III)-singlet with IS = 0.176 ± 0.0288 mm/s from Fe3+ ions in a symmetric environment. The electrical properties of the compound were studied at temperatures of 20 – 450 °C in the frequency range of 25 Hz – 1 MHz. It was found that synthesized ceramics exhibit dielectric properties. The permittivity and the dielectric loss tangent at 20 °C were determined and are 57 and 0.003 (1 MHz), respectively.