Acta Crystallographica Section B

Structural Science

Volume 64, Part 6 (December 2008)

research papers

Acta Cryst. (2008). B64, 652-660 [ doi:10.1107/S0108768108026153 ]

Isosymmetrical phase transition in -YbV₄O₈

K. Friese, Y. Kanke, A. N. Fitch, W. Morgenroth and A. Grzechnik

Abstract: The structure of YbV₄O₈ is related to the CaFe₂O₄ structure type. VO₆ octahedra form a three-dimensional framework with tunnels in which the Yb³⁺ ions are incorporated. Two different polymorphs [alpha] and [beta] are known and differ mainly in the arrangement of the Yb ions within the framework. We studied the structure and magnetic properties of [alpha] -YbV₄O₈ as a function of temperature. At approximately 70 K [alpha] -YbV₄O₈ undergoes a first-order isosymmetrical phase transition (P2₁/n [rightwards arrow] P2₁/n). While in the high-temperature [alpha] phase the three V³⁺ and one V⁴⁺ are disordered over the four symmetrically independent octahedral sites, in the low-temperature [alpha] ' phase complete charge ordering is observed. The transition is accompanied by a paramagnetic-paramagnetic anomaly in the magnetic susceptibility data which can be interpreted on the basis of spin-gap formation. The transition mechanism in the [alpha] polymorph is very similar to that observed earlier in the [beta] polymorph at 185 K.

Keywords: phase transition; polymorphism; magnetic properties; charge ordering.


	Structure factor file (CIF format) (290.4 kbytes) [ doi:10.1107/S0108768108026153/sn5072Isup2.hkl ] Contains datablock I

	Structure factor file (CIF format) (290.0 kbytes) [ doi:10.1107/S0108768108026153/sn5072IIsup3.hkl ] Contains datablock II

	Structure factor file (CIF format) (289.4 kbytes) [ doi:10.1107/S0108768108026153/sn5072IIIsup4.hkl ] Contains datablock III

	Structure factor file (CIF format) (289.2 kbytes) [ doi:10.1107/S0108768108026153/sn5072IVsup5.hkl ] Contains datablock IV

	Structure factor file (CIF format) (262.2 kbytes) [ doi:10.1107/S0108768108026153/sn5072Vsup6.hkl ] Contains datablock V

	Structure factor file (CIF format) (262.7 kbytes) [ doi:10.1107/S0108768108026153/sn5072VIsup7.hkl ] Contains datablock VI

	Structure factor file (CIF format) (262.9 kbytes) [ doi:10.1107/S0108768108026153/sn5072VIIsup8.hkl ] Contains datablock VII

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