Understanding phase transitions in carbonates by investigation of their lattice dynamics by thermal diffuse scattering, high resolution inelastic x-ray scattering, microcalorimetry and density functional theory calculations

• Applicant: Professor Dr. Björn Winkler
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2014 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 258770031

The (pressure, temperature)-phase diagrams of carbonates ACO3, where A = Mg2+, Ca 2+, Fe2+, Sr2+ are often complex. This complexity is, in part, due to the possibility of the CO32--groups to become dynamically disordered at high temperatures. However, the role of dynamic disorder of the CO32- groups has only been investigated in CaCO3-calcite and the findings were inconclusive. Little is known about dynamic disorder in the other carbonates. Here, we propose to study the lattice dynamics and thermodynamics of ACO3 carbonates by high resolution inelastic x-ray scattering, by thermal diffuse scattering, by microcalorimetry and by complementary density functional theory based model calculations. The experimental studies will cover a large composition-, temperature andpressure-range. At ambient pressure, the disorder will be studied up to the decompositiontemperatures. In order to investigate the behavior at high pressure and high temperature, externally heated diamond anvil cells will be employed to reach Pmax = 20 GPa with Tmax = 800 K. For studies at high pressures and even higher temperatures (with Tmax < 2.000 K), a newly developed compact laser-heating system will be employed. The results of the study will be a deeper understanding of the topology of phase diagrams and phase transitions and the resolution of conflicting interpretations of earlier results. The findings will likely be transferable to related systems such as NaNO3.

• DFG Programme: Research Grants
• International Connection: France
• Participating Person: Dr. Alexei Bosak