TY - JOUR

T1 - X-ray powder diffraction studies and thermal behaviour of NaK2B9O15, Na(Na.17K.83)2B9O15, and (Na.80K.20)K2B9O15

AU - Bubnova, R.

AU - Albert, B.

AU - Georgievskaya, M.

AU - Krzhizhanovskaya, M.

AU - Hofmann, K.

AU - Filatov, S.

PY - 2006/9/1

Y1 - 2006/9/1

N2 - 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.

AB - 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.

KW - Borate

KW - Compositional deformation

KW - Rietveld structure refinement

KW - Solid solution

KW - Thermal deformation

UR - http://www.scopus.com/inward/record.url?scp=33747198042&partnerID=8YFLogxK

U2 - 10.1016/j.jssc.2006.06.020

DO - 10.1016/j.jssc.2006.06.020

M3 - Article

AN - SCOPUS:33747198042

VL - 179

SP - 2954

EP - 2963

JO - Journal of Solid State Chemistry

JF - Journal of Solid State Chemistry

SN - 0022-4596

IS - 9

ER -