Raman spectroscopy and X-ray diffraction of sp3-CaCO3 at lower mantle pressures

Crystal structure prediction methods and first-principles calculations have been used to explore low-energy structures of carbon monoxide (CO). Contrary to the standard wisdom, the most stable structure of CO at ambient pressure was found to be a polymeric structure of Pna21 symmetry rather than a molecular solid. This phase is formed from six-membered (4 Carbon + 2 Oxygen) rings connected by C=C double bonds with two double-bonded oxygen atoms attached to each ring. Interest...

Recently discovered class of 2D materials based on transition metal phosphorous trichalcogenides exhibit antiferromagnetic ground state, with potential applications in spintronics. Amongst them, FePS$ _{3} $ is a Mott insulator with a band gap of $\sim$ 1.5 eV. This study using Raman spectroscopy along with first-principles density functional theoretical analysis examines the stability of its structure and electronic properties under pressure. Raman spectroscopy reveals two p...

The behaviour of alkaline carbonates at high pressure is poorly understood. Indeed, theoretical and experimental investigations of general trends of pressure induced structural changes appear in the literature only sporadically. In this article we use a combination of ab-initio calculations and high-pressure experiments in diamond anvil cell to determine crystal structures of high-pressure phases of K2CO3. The comparison with experimental data on Li2CO3 allows to reconstruct ...

A vast amount of Raman spectroscopic data, obtained using diamond anvil cell technique under in situ high pressure-temperature conditions, has been used for mapping the phase transitions of hydrogen in the temperature range of 300 K to 900 K and pressure up to 300 gigapascal, a pressure-temperature region in which most phase information was unknown previously. The isothermal and isobaric dependencies in frequency and peak width for intramolecular vibration Raman mode of hydro...

Based on crystal chemistry considerations and quantum density functional theory ground state calculations, rhombohedral rh-C3 and hexagonal h-C6 carbon allotropes are proposed and energetically calculated as new stable ultra-hard phases likewise lonsdaleite. Along the two kinds of carbon in linear C2-C1-C2 lattice, distorted tetrahedra C2(sp3) with an angle of 106.17{\deg} (smaller than ideal 109.4{\deg}) and C1(sp)-like hybridizations are inferred from charge density project...

Structures of calcium peroxide (CaO2) are investigated in the pressure range 0-200 GPa using the ab initio random structure searching (AIRSS) method and density functional theory (DFT) calculations. At 0 GPa, there are several CaO2 structures very close in enthalpy, with the ground-state structure dependent on the choice of exchange-correlation functional. Further stable structures for CaO2 with C2/c, I4/mcm and P21/c symmetries emerge at pressures below 40 GPa. These phases ...

We report a high-pressure study of tetragonal scheelite-type CaMoO4 up to 29 GPa. In order to characterize its high-pressure behavior, we have combined Raman and optical-absorption measurements with density-functional theory calculations. We have found evidence of a pressure-induced phase transition near 15 GPa. Experiments and calculations agree in assigning the high-pressure phase to a monoclinic fergusonite-type structure. The reported results are consistent with previous ...

Experimental studies established that calcium undergoes several counterintuitive transitions under pressure: fcc \rightarrow bcc \rightarrow simple cubic \rightarrow Ca-IV \rightarrow Ca-V, and becomes a good superconductor in the simple cubic and higher-pressure phases. Here, using ab initio evolutionary simulations, we explore the behavior of Ca under pressure and find a number of new phases. Our structural sequence differs from the traditional picture for Ca, but is simila...

We investigate the effect of pressure, temperature and acidity on the composition of water-rich carbon-bearing fluids at thermodynamic conditions that correspond to the Earth's deep Crust and Upper Mantle. Our first-principles molecular dynamics simulations provide mechanistic insight into the hydration shell of carbon dioxide, bicarbonate and carbonate ions, and on the pathways of the acid/base reactions that convert these carbon species into one another in aqueous solutions...

Solid CS$_{2}$ is superficially similar to CO$_{2}$, with the same $Cmca$ molecular crystal structure at low pressures, which has suggested similar phases also at high pressures. We carried out an extensive first principles evolutionary search in order to identify the zero temperature lowest enthalpy structures of CS$_{2}$ for increasing pressure up to 200\,GPa. Surprisingly, the molecular $Cmca$ phase does not evolve into $\beta$-cristobalite as in CO$_{2}$, but transforms i...