Crystal structure, thermal and compositional deformations of β‐CsB5O8

Abstract

AbstractThe 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, ρcalc = 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: αa = 53, αb = 16, αc = 14 · 10‐6/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. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)