Crystal structure, thermal and compositional deformations of β-CsB5O8 by R. Bubnova, R. E. Dinnebier, S. Filatov, and J. Anderson

Crystal Research and Technology

Cryst. Res. Technol. 42, 143 (2007) - Abstract -

Crystal structure, thermal and compositional deformations of β-CsB₅O₈

R. Bubnova, R. E. Dinnebier*, S. Filatov**, and J. Anderson**

Institute of the Silicate Chemistry Russian Academy of Sciences, Ul. Odoevskogo, 24/2, 199155, St Petersburg, Russia
*Max-Planck Institute for Solid State Research, Heisenbergstrasse 1, 70569 Stuttgart, Germany
**Saint Petersburg State University, University Emb., 7/9, 199034, St. Petersburg, Russia

Keywords	cesium pentaborate, crystal structure, Rietveld refinement, thermal expansion, compositional deformation
PACS	61.10.Nz, 61.66.Fn, 65.40.-b
DOI	10.1002/crat.200610787

The crystal structure of β-CsB₅O₈ has been determined from X-ray powder diffraction data using synchrotron radiation: Pbca, a=7.8131(3) Å, b=12.0652(4) Å, c=14.9582(4) Å, Z=8, ρ_calc = 2.967 g/cm³, R-p=0.076, R-wp=0.094. β-CsB₅O₈ was found to be isostructural with β-KB₅O₈ and β-RbB₅O₈. The crystal structure consists of a double interlocking framework built up from B-O pentaborate groups. The crystal structure exhibits a highly anisotropic thermal expansion: α_a =53, α_b =16, α_c =14x10^-6/K; the anisotropy may be caused by partial straightening of the screw chains of the pentaborate groups. The similarity of the thermal and compositional (Cs-Rb-K substitution) deformations of CsB₅O₈ is revealed: increasing the radius of the metal by 0.01 Å leads to the same deformations of the crystal structure as increasing the temperature by 35°C.

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