Compressional behavior of the aragonite-structure carbonates to 6 GPa.

Abstract

The behavior of aragonite (CaCO3), strontianite (SrCO3 ), cerussite (PbCO3) andwitherite (BaCO3 ) at increasing pressure have been studied up to 6 GPa using density func-tional theory with plane waves. A parallelism of the orthorhombic carbonates with theclosed-packed AsNi structure is considered in our analysis, being the CO2− groups not3centered in the interstice of the octahedron. The decomposition of the unit cell volume intoatomic contributions by using the Quantum Theory of Atoms in Molecules has allowed theanalysis of the bulk modulus in atomic contributions. The bulk, axes, interatomic distancesand atomic compressibilities are calculated. The largest compression is on the c crystallo-graphic axis and the c linear modulus has a linear function with the mineral bulk modulus(K0 ). Many of the interatomic distances moduli of the alkaline earth (AE) carbonates show linear functions with the bulk modulus; however, the whole series (including cerussite) onlygives linear functions when K 0 is related either with the CC distances modulus or the mod-ulus of the distances of the C to the faces of the octahedron perpendicular to c. These lastdistances are the projections of the Metal-Oxygen (MO) distances to the center of the octa-hedron. K 0 AE carbonates also show linear functions with the atomic moduli of their cations,however, the whole series show a linear relation with the atomic modulus of C atoms. There-fore, the whole series highlight the importance of the C atoms and their interactions in themechanism of compression of the orthorhombic carbonate series.