X-ray powder diffraction studies and thermal behaviour of NaK2B9O15, Na(Na.17K.83)2B9O15, and (Na.80K.20)K2B9O15

R. Bubnova, B. Albert, M. Georgievskaya, M. Krzhizhanovskaya, K. Hofmann, S. Filatov

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10 Scopus citations

Abstract

The crystal structures of NaK2B9O15 (a = 9.1158 (1) Å, b = 6.6246 (1) Å, c = 20.6812 (3) Å, β = 94.080 (1) °, Rp = 0.047, Rwp = 0.059, RB = 0.026), Na(Na.17K.83)2B9O15 (a = 9.0559 (1) Å, b = 6.6170 (1) Å, c = 20.5833 (3) Å, β = 94.228 (2) °, Rp = 0.053, Rwp = 0.068, RB = 0.026), and (Na.80K.20)K2B9O15 (a = 9.1534 (1) Å, b = 6.6296 (1) Å, c = 20.7422 (3) Å, β = 94.071 (1) °, Z = 4, Rp = 0.041, Rwp = 0.052, RB = 0.023) were refined in the monoclinic space groups P21/c(Z = 4) using X-ray powder diffraction data and the Rietveld method. These nonaborates are isostructural to K3B9O15. Their crystal structure consists of a three-dimensional open framework built up from three crystallographically independent triborate groups. The alkali metal cations are located on three different sites in the voids of the framework. High-temperature X-ray diffraction studies show that NaK2B9O15 decomposes at about 700 °C in accordance with the peritectic reaction NaK2B9O15↔K5B19O31+liquid. The thermal expansion of NaK2B9O15 and Na(Na.17K.83)2B9O15 is highly anisotropic. A similarity of the thermal and compositional (Na-K substitution) deformations of NaK2B9O15 is revealed: heating of NaK2B9O15 by 1 °C leads to the same deformations of the crystal structure as increasing the amount of K atoms in (Na1-xKx)3B9O15 by 0.04 at% K.

Original languageEnglish
Pages (from-to)2954-2963
Number of pages10
JournalJournal of Solid State Chemistry
Volume179
Issue number9
DOIs
StatePublished - 1 Sep 2006

Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Condensed Matter Physics
  • Physical and Theoretical Chemistry
  • Inorganic Chemistry
  • Materials Chemistry

Keywords

  • Borate
  • Compositional deformation
  • Rietveld structure refinement
  • Solid solution
  • Thermal deformation

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Dive into the research topics of 'X-ray powder diffraction studies and thermal behaviour of NaK<sub>2</sub>B<sub>9</sub>O<sub>15</sub>, Na(Na<sub>.17</sub>K<sub>.83</sub>)<sub>2</sub>B<sub>9</sub>O<sub>15</sub>, and (Na<sub>.80</sub>K<sub>.20</sub>)K<sub>2</sub>B<sub>9</sub>O<sub>15</sub>'. Together they form a unique fingerprint.

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