Synthetic norsethite, BaMg(CO<sub>3</sub>)<sub>2</sub>
- Author(s)
- Herta Silvia Effenberger, Thomas Pippinger, Eugen Libowitzky, Christian Lengauer, Ronald Miletich-Pawliczek
- Abstract
The crystal structure of synthetic BaMg(CO
3)
2 whose mineral name is norsethite was re-investigated by single-crystal X-ray diffraction. Complementary in situ high-and lowerature studies by means of vibrational spectroscopy (Raman, IR), powder X-ray diffraction techniques and thermal analyses were performed. Diffraction images (298 K) revealed weak superstructure reflections caused by the displacement of the O atoms in the earlier considered R3m structure model (a = 5.0212(9), c
new = 2c
old = 33.581(6) Å, R3c, Z = 6, R1 = 0.011, sinθ/λ < 0.99 Å
-1). Thermal analyses reveal decarbonatization in two decomposition steps above 750 K, and the heat-flow curves (difference scanning calorimetry) give clear evidence of a weak and reversible endothermal change at 343±1 K. This agrees with a discontinuity in the IR and single-crystal Raman spectra. The changing trend of the c/a ratio supports this discontinuity indicating a temperature-induced structural transition in the range between 343 and 373 K. As the change of the unit-cell volume is almost linear, the character of the transition is apparently second order and matches the mechanism of a subtle displacement of the oxygen atom position. The apparent instability of the R3c structure is also evidenced by the remarkably larger anisotropic displacement of the oxygen atom.
- Organisation(s)
- Department of Mineralogy and Crystallography
- Journal
- Mineralogical Magazine
- Volume
- 78
- Pages
- 1589-1611
- No. of pages
- 23
- ISSN
- 0026-461X
- DOI
- https://doi.org/10.1180/minmag.2014.078.7.05
- Publication date
- 12-2014
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 105116 Mineralogy, 104017 Physical chemistry, 104011 Materials chemistry, 105113 Crystallography
- Keywords
- ASJC Scopus subject areas
- Geochemistry and Petrology
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/synthetic-norsethite-bamgco32(c3b20626-7d23-4e27-a66f-5fb021746a94).html