Stability of CO2 and carbonate materials under extreme conditions

Carbon dioxide (CO2) in its free and anionic forms (carbonates and bicarbonates) is an essential component of the Earth's carbon cycle and a major contributor to climate change. A detailed knowledge of CO2 dynamics and stability under high pressure and temperature is essential to understand the Earth's carbon cycle as well as to design new strategies for separation and capture of CO2. Despite this, our current knowledge of the pressure-temperature phase diagram of many geologically relevant carbonates is fragmentary. In this talk, we present a combined computational and experimental study of the phase stability of CO2 and various carbonates of geological relevance: hunitite (Mg3Ca(CO3)4), ankerite (CaFe(CO3)2), alstonite (BaCa(CO3)2), gaspeite (Ni3Mg(CO3)4), and others. This work has been carried out using laser-heating and diamond-anvil cell synchrotron X-ray diffraction in order to recreate the pressure and temperature that dominate in the interior of the Earth. Density-functional theory calculations are used to predict the stability and structure of these phases under arbitrary conditions of temperature and pressure. Conclusions are drawn regarding the general behavior of carbonates and CO2 under extreme conditions and their potential geological relevance.