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Zeitschrift für Kristallographie - Crystalline Materials

Ed. by Antipov, Evgeny / Bismayer, Ulrich / Huppertz, Hubert / Petrícek, Václav / Pöttgen, Rainer / Schmahl, Wolfgang / Tiekink, E. R. T. / Zou, Xiaodong

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Sodium hydrogencarbonate (NaHCO3): coincidence-site lattice twinning and structure refinement

Michael E. Fleet1 / Xi Liu2

1 University of Western Ontario, Department of Earth Sciences, Ontario N6A 5B7, Kanada

2 Kanada

* Correspondence address: Richmond Street, N6A 5B7 London,

Citation Information: Zeitschrift für Kristallographie International journal for structural, physical, and chemical aspects of crystalline materials. Volume 224, Issue 3, Pages 144–150, ISSN (Print) 0044-2968, DOI: 10.1524/zkri.2009.1036, September 2009

Publication History:
Published Online:
2009-09-25

Abstract

Sodium hydrogencarbonate (NaHCO3) has been recrystallised hydrothermally using a cooling ramp from 250 °C to 190 °C at 0.069 GPa, and investigated by single crystal X-ray diffraction at room temperature and pressure. Representative crystal data are: monoclinic, space group P21/n, Z = 4, a = 7.4688(4), b = 9.6842(6), c = 3.4791(2) Å, β = 93.321(2)°, R = 0.026, and Dx = 2.221 g/cm3. The crystals investigated are complexly twinned by reticular pseudomerohedry, but give two coincidence-site lattices with pseudocell parameters: a = 3.4791(2), b = 9.6842(6), c = 29.875(2) Å, β = 93.321(2)°, twin axis [001], twin index (Σ) = 4; and, a = 8.4360(6), b = 9.6811(7), c = 24.941(2) Å, β = 99.109(5)°, twin axis [10-1], Σ = 8. The Σ = 4 and Σ = 8 twins occur in separate twinned crystals but in similar twin proportions (5.5 : 1), and are most likely secondary in origin. The two coincidence-site lattices are permitted in NaHCO3 because β corresponds closely to the theoretical value given by the positive root of [sin2 (β – π/2) = 3/912].

Keywords: Sodium hydrogencarbonate; Twinning; Coincidence-site lattices; Single crystal structure analysis; X-ray diffraction

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