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Structural properties in RFe2O4 compounds (R = Tm, Yb, and Lu)

AutorBlasco, Javier; Lafuerza, Sara; García, Joaquín; Subías, G.
Fecha de publicación2014
EditorAmerican Physical Society
CitaciónPhysical Review B 90: 094119 (2014)
ResumenWe report a complete characterization of the crystal structure between 400 and 80 K for RFe2O4 (R = Rm, Yb, and Lu) compounds using high resolution x-ray synchrotron powder diffraction. The three samples have a hexagonal structure (space group R3¯m) characterized by a sequence of double layers of mixed valence iron and oxygen atoms forming two-dimensional triangular layers separated by a single R-O layer along the c axis. This structure is stable down to 80 K for TmFe2O4 and YbFe2O4 though a sudden expansion in the c axis is observed at around 300 K coupled to a variation in the electrical properties. However, LuFe2O4 exhibits two structural transitions upon cooling. The splitting of some reflections and the occurrence of superstructure peaks below 320 K reveal a structural phase transition. The unit cell is monoclinic (space group C2/m), and there are four nonequivalent Fe sites with a maximum charge disproportionation of 0.5 e. The hexagonal to monoclinic transition is characterized by a sudden expansion of the c axis on cooling, and it seems to be driven by the condensation of Y2 modes. At lower temperatures (~170 K) additional splitting of several peaks indicate that the unit cell is no longer monoclinic but triclinic (space group P1¯). This transition is characterized by a contraction of the monoclinic ab plane, while the c axis remains almost unchanged. There are six nonequivalent Fe sites in the triclinic cell, and the charge disproportionation magnitude is little affected.
DescripciónUnder the terms of the Creative Commons Attribution License 3.0 (CC-BY).
Versión del editorhttp://dx.doi.org/10.1103/PhysRevB.90.094119
Identificadoresdoi: 10.1103/PhysRevB.90.094119
issn: 1098-0121
e-issn: 1550-235X
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