On the crystal structures of Ln{sub 3}MO{sub 7} (Ln=Nd, Sm, Y and M=Sb, Ta)-Rietveld refinement using X-ray powder diffraction data

Journal Article · Tue Sep 15 00:00:00 EDT 2009 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2009.06.028· OSTI ID:21370576

IJdo, D J.W. ^[1]

---

1. Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, P.O. Box 9502, 2300 RA Leiden (Netherlands)

We have investigated, using X-ray powder diffraction data, the crystal structures of some fluorite derivatives with the formula Ln{sub 3}MO{sub 7} (Ln=lanthanide or Y and M=Sb and Ta). In these compounds ordering of Ln and M occurs, leading to a parent structure in Cmmm. Tilting of the MO{sub 6} octahedra causes doubling of one of the cubic axes, leading to a number of non-isomorphic subgroups, e.g. Cmcm, Ccmm and Cccm. We have identified an alternative space group Ccmm instead of C222{sub 1} for those compounds containing a medium sized lanthanide or Y and M being Sb or Ta. Interestingly this is an alternative setting for the space group of the structure obtained when Ln is large (Cmcm). However, there tilting of the octahedra is around the a-axis of the parent structure, rather than around the b-axis as it is found in the compounds which we are reporting on here. In one compound, Nd{sub 3}TaO{sub 7}, both tilts occur. The phase transition between the two possible structures is a slow and difficult process above 80 K, allowing both phases to coexist. - Graphical abstract: (a) A projected view of Ln{sub 3}MO{sub 7} along the a-axis showing the ordering of Ln and M cations in the fluoride lattice. Note that the unit cells of the fluorite (dashed line), the parent Cmmm (dashed line) and the Cmcm/Ccmm structures (continuous line) are indicated. (b) Schematic representations of the crystal structures of Y{sub 3}SbO{sub 7} showing SbO{sub 6} octahedra and Y. Oxygens that do not bond to M cations are also shown.

• OSTI ID: 21370576
• Journal Information: Journal of Solid State Chemistry, Vol. 182, Issue 9; Other Information: DOI: 10.1016/j.jssc.2009.06.028; PII: S0022-4596(09)00289-8; Copyright (c) 2009 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; ISSN 0022-4596
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ANTIMONY COMPOUNDS
CATIONS
NEODYMIUM COMPOUNDS
ORTHORHOMBIC LATTICES
OXIDES
PHASE TRANSFORMATIONS
SAMARIUM COMPOUNDS
SPACE GROUPS
TANTALUM COMPOUNDS
TEMPERATURE RANGE 0065-0273 K
X-RAY DIFFRACTION
YTTRIUM COMPOUNDS
CHALCOGENIDES
CHARGED PARTICLES
COHERENT SCATTERING
CRYSTAL LATTICES
CRYSTAL STRUCTURE
DIFFRACTION
IONS
OXYGEN COMPOUNDS
RARE EARTH COMPOUNDS
REFRACTORY METAL COMPOUNDS
SCATTERING
SYMMETRY GROUPS
TEMPERATURE RANGE
TRANSITION ELEMENT COMPOUNDS