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Tetrapotassium pyrophosphates γ- and δ-K4P2O7

Published online by Cambridge University Press:  13 March 2013

Armel Le Bail ,
Thomas Hansen  and
Wilson A. Crichton
Armel Le Bail*
Affiliation:
Institut des Molécules et des Matériaux du Mans, CNRS UMR 6283, Université du Maine, Avenue O. Messiaen, 72085 Le Mans, France
Thomas Hansen
Affiliation:
Institut Laue Langevin, 38042 Grenoble, France
Wilson A. Crichton
Affiliation:
European Synchrotron Radiation Facility, BP 220, 38043 Grenoble, France
*
a)Author to whom correspondence should be addressed. Electronic mail: armel.le_bail@univ-lemans.fr
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Abstract

The structures of γ- and δ-K4P2O7 are solved by X-ray powder diffraction (conventional laboratory X-ray and synchrotron data, respectively), both in hexagonal symmetry (aγ = 5.9645(3) Å, cγ = 14.4972(8) Å, Vγ = 446.64(4) Å3 at 300 °C, Zγ = 2, space group P63/mmc; aδ = 10.211 45(7) Å, cδ = 42.6958(4) Å, Vδ = 3855.59(7) Å3 at room temperature, Zδ = 18, space group P61) with cell–supercell relations $a_\delta \approx a_\gamma \sqrt{3}$ and cδ ≈ 3 cγ. In the experimental conditions, the expected β/γ transition previously announced at 486 °C is not observed; the γ-form is stable at least up to the maximum temperature of our measurements (700 °C). In the γ-form, similar to the orthorhombic form of Na4P2O7, idealized, the pyrophosphate group is in eclipsed conformation, the K+ cations occupying three different coordinations. In the δδ-form, two of the three different [P2O7]4− groups are staggered and one eclipsed, the K+ cations occupying 12 independent sites.

Keywords

tetrapotassium pyrophosphatepowder diffractioncrystal structureab initio

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Type
Technical Articles
Information
Powder Diffraction , Volume 28 , Issue 1 , March 2013 , pp. 2 - 12
Copyright
Copyright © International Centre for Diffraction Data 2013 

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