Acta Crystallographica Section B

Structural Science, Crystal Engineering and Materials

Volume 69, Part 2 (April 2013)


research papers



Acta Cryst. (2013). B69, 137-144    [ doi:10.1107/S2052519213003126 ]

Anisotropic thermal expansion of Lan(Ti,Fe)nO3n + 2 (n = 5 and 6)

A. Wölfel, P. Dorscht, F. Lichtenberg and S. van Smaalen

Abstract: Crystal structures are reported for two perovskite-related compounds with nominal compositions La5(Ti0.8Fe0.2)5O17 and La6(Ti0.67Fe0.33)6O20 at seven different temperatures between 90 and 350 K. For both compounds no evidence of a structural phase transition in the investigated range of temperatures was found. The thermal expansions are found to be anisotropic, with the largest thermal expansion along a direction parallel to the slabs of these layered compounds. The origin of this anisotropy is proposed to be a temperature dependence of tilts of the octahedral (Ti,Fe)O6 groups. It is likely that the same mechanism will determine similar anisotropic thermal behaviour of other compounds AnBnO3n + 2. The crystal structures have revealed partial chemical order of Ti/Fe over the B sites, with iron concentrated towards the centers of the slabs. Local charge compensation is proposed as the driving force for the chemical order, where the highest-valent cation moves to sites near the oxygen-rich borders of the slabs. A linear dependence on the site occupation fraction by Fe of the computed valences leads to extrapolated valence values close to the formal valence of Ti4+ for sites fully occupied by Ti, and of Fe3+ for sites fully occupied by Fe. These results demonstrate the power of the bond-valence method, and they show that refined oxygen positions are the weighted average of oxygen positions in TiO6 and FeO6 octahedral groups.

B-IncStrDB reference: 6872EpvgNl

Keywords: perovskites; thermal expansion; phase transitions; order; bond-valence method.


hkldisplay filedownload file

Structure factor file (CIF format) (353.5 kbytes)
[ doi:10.1107/S2052519213003126/bp5048n5_090Ksup2.hkl ]
Contains datablock n5_090K


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Structure factor file (CIF format) (198.5 kbytes)
[ doi:10.1107/S2052519213003126/bp5048n5_150Ksup3.hkl ]
Contains datablock n5_150K


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Structure factor file (CIF format) (322.5 kbytes)
[ doi:10.1107/S2052519213003126/bp5048n5_200Ksup4.hkl ]
Contains datablock n5_200K


hkldisplay filedownload file

Structure factor file (CIF format) (324.5 kbytes)
[ doi:10.1107/S2052519213003126/bp5048n5_250Ksup5.hkl ]
Contains datablock n5_250K


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Structure factor file (CIF format) (257.1 kbytes)
[ doi:10.1107/S2052519213003126/bp5048n5_295Ksup6.hkl ]
Contains datablock n5_295K


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Structure factor file (CIF format) (312.5 kbytes)
[ doi:10.1107/S2052519213003126/bp5048n5_320Ksup7.hkl ]
Contains datablock n5_320K


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Structure factor file (CIF format) (626.7 kbytes)
[ doi:10.1107/S2052519213003126/bp5048n5_350Ksup8.hkl ]
Contains datablock n5_350K


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Structure factor file (CIF format) (812.9 kbytes)
[ doi:10.1107/S2052519213003126/bp5048n6_090Ksup9.hkl ]
Contains datablock n6_090K


hkldisplay filedownload file

Structure factor file (CIF format) (819.2 kbytes)
[ doi:10.1107/S2052519213003126/bp5048n6_140Ksup10.hkl ]
Contains datablock n6_140K


hkldisplay filedownload file

Structure factor file (CIF format) (810.4 kbytes)
[ doi:10.1107/S2052519213003126/bp5048n6_200Ksup11.hkl ]
Contains datablock n6_200K


hkldisplay filedownload file

Structure factor file (CIF format) (818.9 kbytes)
[ doi:10.1107/S2052519213003126/bp5048n6_250Ksup12.hkl ]
Contains datablock n6_250K


hkldisplay filedownload file

Structure factor file (CIF format) (800.2 kbytes)
[ doi:10.1107/S2052519213003126/bp5048n6_295Ksup13.hkl ]
Contains datablock n6_295K


hkldisplay filedownload file

Structure factor file (CIF format) (791.7 kbytes)
[ doi:10.1107/S2052519213003126/bp5048n6_320Ksup14.hkl ]
Contains datablock n6_320K


hkldisplay filedownload file

Structure factor file (CIF format) (816.2 kbytes)
[ doi:10.1107/S2052519213003126/bp5048n6_350Ksup15.hkl ]
Contains datablock n6_350K


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