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)相图往往比较复杂，其中A=镁、钙、铁、锶。这种复杂性在一定程度上是由于CO32-基团在高温下动态无序的可能性。然而，CO32-基团的动态无序的作用只在CaCO3-方解石中被研究过，结果并不确定。人们对其他碳酸盐中的动态无序知之甚少。在这里，我们建议用高分辨非弹性x射线散射、热扩散散射、微量热和基于互补密度泛函理论的模型计算来研究ACO3碳酸盐的晶格动力学和热力学。实验研究将涵盖很大的组成、温度和压力范围。在常压下，这种无序将被研究到分解温度。为了研究其在高温高压下的行为，将采用外部加热的金刚石顶压室，以达到Pmax=20 Gpa，Tmax=800K。对于高压和更高温度(Tmax和lt；2.000 K)的研究，将使用新开发的紧凑型激光加热系统。研究的结果将是更深入地理解相图和相变的拓扑结构，并解决对先前结果的相互矛盾的解释。这些发现可能会被转移到相关系统，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.