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Metastable (Bi, M)2(Fe, Mn, Bi)2O6+x (M = Na or K) Pyrochlores from Hydrothermal Synthesis

DOI: 10.1021/ic502411z DOI Help

Authors: Luke Daniels (Department of Chemistry, University of Warwick) , Helen Playford (ISIS Facility, Rutherford Appleton Laboratory) , Jean-marc Grenèche (Institut des Molecules et des Matériaux du Mans, UMR 6283—CNRS LUNAM Université du Maine) , Alex Hannon (ISIS Facility, Rutherford Appleton Laboratory) , Richard Walton (Department of Chemistry, University of Warwick)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Inorganic Chemistry , VOL 53 (24) , PAGES 13197 - 13206

State: Published (Approved)
Published: December 2014
Diamond Proposal Number(s): 8189

Abstract: The hydrothermal syntheses, structures, and magnetism of two new pyrochlore oxides of compositions (Na0.60Bi1.40)(Fe1.06Mn0.17Bi0.77)O6.87 and (K0.24Bi1.51)(Fe1.07Mn0.15Bi0.78)O6.86 are described. With preparation at 200 °C for 6 h in solutions of sodium or potassium hydroxide, the alkali metals introduced from these mineralizers are essential to the synthesis of the phases. The average long-range order of the pyrochlore structure, with space group Fd3m, was investigated and refined against X-ray and neutron diffraction data, and it was shown that disorder is present in both the metal and coordinating oxygen positions, along with metal-mixing across both the A and B sites of the structure. XANES analysis confirms the presence of Mn4+, mixed valence Bi3+ and Bi5+, and Fe3+, the last also verified by 57Fe Mössbauer spectroscopy. Magnetic measurements show a lack of long-range magnetic ordering that is typical of geometrically frustrated pyrochlores. The observed glasslike interactions occur at low temperatures, with the onset temperature depending upon the magnitude of the applied external field. Variable temperature X-ray diffraction shows that these pyrochlores are metastable and collapse on heating at ca. 395 °C, which suggests that their formation by conventional solid-state synthesis would be impossible.

Subject Areas: Chemistry


Instruments: B18-Core EXAFS

Added On: 06/02/2015 07:25

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