Acta Crystallographica Section B

Structural Science

Volume 59, Part 3 (June 2003)

research papers

Acta Cryst. (2003). B59, 337-352 [ doi:10.1107/S0108768103009017 ]

Sodium carbonate revisited

M. Dusek, G. Chapuis, M. Meyer and V. Petricek

Abstract: We present the structure of anhydrous sodium carbonate at room temperature (phase [bold gamma] ) and 110 K (phase [bold delta] ) based on single-crystal X-ray diffraction data. The incommensurate phase was determined almost 30 years ago in the harmonic approximation using one modulation wave and first-order satellites. In our work we use satellites up to fifth order and additional harmonic waves to model the anharmonic features of the structure. The commensurate phase [bold delta] is presented for the first time. Using the superspace approach, both phases are compared in order to find common trends in the whole range of the sodium carbonate phases. We present arguments supporting the hypothesis that the driving force of the phase transitions may originate in the unsaturated bonding potential of one of the Na ions.

Keywords: modulated structure; aperiodic structure; phase transition; commensurate refinement.


	Structure factor file (CIF format) (530.8 kbytes) Contains datablock I

	Structure factor file (CIF format) (177.7 kbytes) Contains datablock II

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