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

碳酸盐ACO3的（压力，温度）相图通常是复杂的，其中A = Mg2+, ca2 +, Fe2+, Sr2+。这种复杂性部分是由于CO32-基团在高温下可能变得动态无序。然而，CO32-基团的动态失序作用仅在caco3 -方解石中进行了研究，结果尚无定论。对其他碳酸盐岩的动态失序知之甚少。在这里，我们提出通过高分辨率非弹性x射线散射、热漫射散射、微量热法和基于互补密度泛函数理论的模型计算来研究ACO3碳酸盐的晶格动力学和热力学。实验研究将涵盖一个大的成分、温度和压力范围。在环境压力下，将研究直至分解温度的无序性。为了研究在高压和高温下的行为，将采用外部加热的金刚石砧细胞达到Pmax = 20 GPa, Tmax = 800 K。对于高压甚至更高温度（Tmax < 2.000 K）的研究，将采用新开发的紧凑型激光加热系统。这项研究的结果将是对相图和相变的拓扑结构的更深入的理解，以及对早期结果的相互矛盾的解释的解决。这些发现可能会转移到相关的系统，如NaNO3。

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.