The high-pressure diffraction studies of potassium and complex carbonates: structural trends and stability
- Dr. Sergey RASHCHENKO
- Dr. Sergey DEMENTIEV (Institute of geology and mineralogy SD RAS)
- Dr. Sergey GORYAINOV (Institute of geology and mineralogy SD RAS)
- Dr. Pinelli S.R. PRASAD (National Geophysical Research Institute, Hyderabad (India))
- Mr. Alexey ANCHAROV (Institute of Solid State Chemistry and Mechanochemistry SB RAS)
The interest to carbonates is determined by their obvious practical importance, as well as their abundance in the Earth’s interior and a key role in magma generation, plume upwelling and diamond growth . Despite the structural trend of the high-temperature phases of all alkaline carbonates is well understood , almost nothing is known about high-pressure behavior of these compounds. In this work we use a combination of the high-pressure diffraction experiments in diamond anvil cell (4th beamline of the VEPP-3 storage ring of the SSTRC, Novosibirsk) and ab-initio calculations to determine the crystal structure of the high-pressure phase of K2CO3 at 3.1 GPa. Among the structures founded in our calculations, the Р21/с-structure shows relevant matching with the experimental pattern (Fig. 1). The comparison with the experimental data on Li2CO3 allows to reconstruct the common structural trend, which is consistent with the simple rule that the structure of the high-pressure polymorph is the same as the ambient structure of a heavier element compound from the same group of the periodic table. We also report on the compressibility and structure behaviour of thaumasite Ca3Si(OH)6(CO3)(SO4)•12Н2О, a unique known mineral that possesses Si coordinated by six hydroxyl groups and stable at ambient P/Tconditions . Our data show a strong dependence of its high-pressure stability limit on the nature of compressing medium. This work is supported by the Russian Foundation for Basic Research (grant No 15-55-45070) and the Ministry of Education and Science of Russian Federation (# 14.B25.31.0032).
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