Acta Crystallographica Section C

Crystal Structure Communications

Volume 61, Part 12 (December 2005)

inorganic compounds

Acta Cryst. (2005). C61, i113-i116 [doi:10.1107/S010827010503249X]

Powder neutron diffraction of Tl₂BeF₄ at six temperatures from room temperature to 1.5 K

I. da Silva, C. González-Silgo, J. González-Platas, J. Rodríguez-Carvajal, M. L. Martínez-Sarrión and L. Mestres

Abstract: The structure of thallium fluoroberyllate, Tl₂BeF₄, has been analysed by the Rietveld method on neutron diffraction patterns collected at 1.5, 50, 100, 150, 200 and 300 K, with the aim of detecting low-temperature instabilities. Atomic parameters based on the isomorphic [beta] -K₂SO₄ crystal in the paraelectric phase were used as the starting model at room temperature; no evidence for any phase transition has been detected at lower temperature. The structure was determined in the orthorhombic space group Pnma. All the atoms (except one F atom) occupy sites with m symmetry. We have compared the structure with those of other compounds of the [beta] -K₂SO₄ family, at room temperature, in order to gain insight into their observed instabilities. The irregular coordination of the cations may indicate stereochemical activity of the Tl^I lone pair but does not indicate a possible structural instability.

Formula: Tl₂BeF₄


	Rietveld powder data file (CIF format) (169.4 kbytes) Contains datablock I_300K

	Rietveld powder data file (CIF format) (169.2 kbytes) Contains datablock I_200K

	Rietveld powder data file (CIF format) (169.2 kbytes) Contains datablock I_150K

	Rietveld powder data file (CIF format) (169.2 kbytes) Contains datablock I_100K

	Rietveld powder data file (CIF format) (169.2 kbytes) Contains datablock I_50K

	Rietveld powder data file (CIF format) (169.2 kbytes) Contains datablock I_1.5K

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