Acta Crystallographica Section B

Structural Science

Volume 64, Part 3 (June 2008)

research papers

Acta Cryst. (2008). B64, 272-280 [ doi:10.1107/S0108768108005119 ]

Vacancy-ordering effects in AlB₂-type ErGe_{2 - x} (0.4 < x 0.5)

J. Christensen, S. Lidin, B. Malaman and G. Venturini

Abstract: In the Er-Ge system, the compostion range ErGe₂ to Er₂Ge₃ has been investigated. Eight samples were produced by arc melting of the elements, and analyzed using X-ray powder diffraction. Nine crystal structures were found to be present in the samples. The structures are described as a homologous series and presented within the superspace formalism using the superspace group X2/m( [alpha] 0 [gamma] )0s, X representing the centring vector (½, ½, 0, ½). In this description the modulation vector q = ( [alpha] a* + [gamma] c*) is shown to be a direct measure of the Ge content as ErGe_2 - ( [alpha] falls in the range $1\over 3$ to ½). The large composition range is achieved by extended vacancy ordering in the planar 6³ net of Ge with subsequent relaxation.

Keywords: modulation; rare-earth germanides; vacancy ordering.


	Rietveld powder data file (CIF format) (220.5 kbytes) [ doi:10.1107/S0108768108005119/ck5030Isup2.rtv ] Contains datablock I

	Rietveld powder data file (CIF format) (444.4 kbytes) [ doi:10.1107/S0108768108005119/ck5030IIsup3.rtv ] Contains datablock II

	Rietveld powder data file (CIF format) (444.4 kbytes) [ doi:10.1107/S0108768108005119/ck5030IIIsup4.rtv ] Contains datablock III

	Rietveld powder data file (CIF format) (504.5 kbytes) [ doi:10.1107/S0108768108005119/ck5030IVsup5.rtv ] Contains datablock IV

	Rietveld powder data file (CIF format) (504.5 kbytes) [ doi:10.1107/S0108768108005119/ck5030Vsup6.rtv ] Contains datablock V

	Rietveld powder data file (CIF format) (504.5 kbytes) [ doi:10.1107/S0108768108005119/ck5030VIsup7.rtv ] Contains datablock VI

	Rietveld powder data file (CIF format) (504.5 kbytes) [ doi:10.1107/S0108768108005119/ck5030VIIsup8.rtv ] Contains datablock VII

	Rietveld powder data file (CIF format) (504.5 kbytes) [ doi:10.1107/S0108768108005119/ck5030VIIIsup9.rtv ] Contains datablock VIII

	Rietveld powder data file (CIF format) (504.5 kbytes) [ doi:10.1107/S0108768108005119/ck5030IXsup10.rtv ] Contains datablock IX

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