Thermal expansion of gehlenite, Ca2Al[AlSiO7], and the related aluminates LnCaAl[Al2O7] with Ln = Tb, Sm |
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Authors: | L Peters K Knorr M Knapp W Depmeier |
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Institution: | 1. Institut für Geowissenschaften, Abt. Mineralogie/Kristallographie, Christian-Albrechts-Universit?t, Olshausenstra?e 40, 24098, Kiel, Germany 2. Institute for Materials Science, Darmstadt University of Technology, Petersenstra?e 23, 64287, Darmstadt, Germany 3. HASYLAB/DESY, Notkestr. 85, 22607, Hamburg, Germany
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Abstract: | The thermal expansion of gehlenite, Ca2AlAlSiO7], (up to T=830 K), TbCaAlAl2O7] (up to T=1100 K) and SmCaAlAl2O7] (up to T=1024 K) has been determined. All compounds are of the melilite structure type with space group
Thermal expansion data were obtained from in situ X-ray powder diffraction experiments in-house and at HASYLAB at the Deutsches
Elektronen Synchrotron (DESY) in Hamburg (Germany). The thermal expansion coefficients for gehlenite were found to be: α1=7.2(4)×10−6×K−1+3.6(7)×10−9ΔT×K−2 and α3=15.0(1)×10−6×K−1. For TbCaAlAl2O7] the respective values are: α1=7.0(2)×10−6×K−1+2.0(2)×10−9ΔT×K−2 and α3=8.5(2)×10−6×K−1+2.0(3)×10−9ΔT×K−2, and the thermal expansion coefficients for SmCaAlAl2O7] are: α1=6.9(2)×10−6×K−1+1.7(2)×10−9ΔT×K−2 and α3=9.344(5)×10−6×K−1. The expansion mechanisms of the three compounds are explained in terms of structural trends obtained from Rietveld refinements
of the crystal structures of the compounds against the powder diffraction patterns. No structural phase transitions have been
observed. While gehlenite behaves like a ‘proper’ layer structure, the aluminates show increased framework structure behavior.
This is most probably explained by stronger coulombic interactions between the tetrahedral conformation and the layer-bridging
cations due to the coupled substitution (Ca2++Si4+)–(Ln
3++Al3+) in the melilite-type structure.
This article has been mistakenly published twice. The first and original version of it is available at . |
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Keywords: | Gehlenite Melilite Coupled substitution Thermal expansion |
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