X-ray powder diffraction studies and thermal behaviour of NaK{sub 2}B{sub 9}O{sub 15}, Na(Na{sub .17}K{sub .83}){sub 2}B{sub 9}O{sub 15}, and (Na{sub .80}K{sub .20})K{sub 2}B{sub 9}O{sub 15}
- Grebenshchikov Institute of Silicate Chemistry, RAS, St. Petersburg, 199155 (Russian Federation)
- Eduard-Zintl-Institut fur Anorganische und Physikalische Chemie, Technische Universitaet Darmstadt, 64287 Darmstadt (Germany)
- Department of Crystallography, St. Petersburg State University, St. Petersburg 199034 (Russian Federation)
The crystal structures of NaK{sub 2}B{sub 9}O{sub 15} (a=9.1158(1)A, b=6.6246(1)A, c=20.6812(3)A, {beta}=94.080(1){sup o}, R{sub p}=0.047, R{sub wp}=0.059, R{sub B}=0.026), Na(Na{sub .17}K{sub .83}){sub 2}B{sub 9}O{sub 15} (a=9.0559(1)A, b=6.6170(1)A, c=20.5833(3)A, {beta}=94.228(2){sup o}, R{sub p}=0.053, R{sub wp}=0.068, R{sub B}=0.026), and (Na{sub .80}K{sub .20})K{sub 2}B{sub 9}O{sub 15} (a=9.1534(1)A, b=6.6296(1)A, c=20.7422(3)A, {beta}=94.071(1){sup o}, Z=4, R{sub p}=0.041, R{sub wp}=0.052, R{sub B}=0.023) were refined in the monoclinic space groups P2{sub 1}/c(Z=4) using X-ray powder diffraction data and the Rietveld method. These nonaborates are isostructural to K{sub 3}B{sub 9}O{sub 15}. 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 NaK{sub 2}B{sub 9}O{sub 15} decomposes at about 700deg. C in accordance with the peritectic reaction NaK{sub 2}B{sub 9}O{sub 15}-bar K{sub 5}B{sub 19}O{sub 31}+liquid. The thermal expansion of NaK{sub 2}B{sub 9}O{sub 15} and Na(Na{sub .17}K{sub .83}){sub 2}B{sub 9}O{sub 15} is highly anisotropic. A similarity of the thermal and compositional (Na-K substitution) deformations of NaK{sub 2}B{sub 9}O{sub 15} is revealed: heating of NaK{sub 2}B{sub 9}O{sub 15} by 1 deg. C leads to the same deformations of the crystal structure as increasing the amount of K atoms in (Na{sub 1-x}K{sub x}){sub 3}B{sub 9}O{sub 15} by 0.04at% K.
- OSTI ID:
- 20905464
- Journal Information:
- Journal of Solid State Chemistry, Vol. 179, Issue 9; Conference: 15. international symposium on boron, borides and related compounds, Hamburg (Germany), 21-26 Aug 2005; Other Information: DOI: 10.1016/j.jssc.2006.06.020; PII: S0022-4596(06)00343-4; Copyright (c) 2006 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0022-4596
- Country of Publication:
- United States
- Language:
- English
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