Metastability and crystallisation of metamict minerals

在自然界中，变质矿物暴露于α辐照，破坏了结构的周期性，导致一种持续的短程有序状态，但违反了长程有序。这种材料是在异质、无定形或准无定形基质中的晶体簇的混合物，与它们的有序对应物相比，具有显著改变的材料性质。在热处理过程中，亚稳相可以恢复，并且取决于其结构损伤的原始状态，材料在局部直至宏观长度尺度上显示成核和再结晶特征。原子重排，动力学行为和重组的多面体基团的连接，以远程订单，以及在一些选定的变质矿物（烧绿石和钛铁矿与不同的杂质和程度的变质）的原位有序将进行研究。对局部长度尺度敏感的方法和综合实验技术将用于显示和分析结构重排和有序的细节，以便将局部现象与宏观材料行为相关联，并模拟材料的结晶和平衡特征。

In nature metamict minerals are exposed to alpha-irradiation which destroys the structural periodicity and leads to a state with persisting short-range order but violated long-rage order. Such materials are a mixture of crystalline clusters in a heterogeneous, amorpous or quasi-amorphous matrix with drastically altered material properties compared with their ordered counterparts. During thermal treatment the metastable phase can recover and depending on its original state of structural damage the material shows nucleation and recrystallisation features on the local up to the macroscopic length scale. The atomic rearrangement, the kinetic behaviour and restructuring of the connectivity of polyhedral groups up to long-range oder as well as the in-situ ordering in some selected metamict minerals (pyrochlore and titanite with different impurities and degrees of metamictisation) will be studied. Methods sensitive on the local length scale and integrating experimental techniques will be used to display and characterise details of the structural rearrangement and ordering, in order to correlate local phenomena with the macroscopic materials behaviour and to model crystallisation and equilibration features of the materials.