Metastability and crystallisation of metamict minerals

在自然界中，变质岩矿物受到α -辐照后，其结构周期性被破坏，形成了一种短期有序而长期无序的状态。这种材料是在非均质、非晶或准非晶基质中的晶体团簇的混合物，与有序的材料相比，材料性质发生了巨大的变化。在热处理过程中，亚稳相可以恢复，并且根据其原始结构损伤状态，材料在局部到宏观长度尺度上表现出成核和再结晶特征。本文将研究不同杂质和不同变质程度的辉绿石和钛矿的原子重排、多面体基团的动力学行为和连系的重构以及原位有序。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描述结构重排和排序的细节，以便将局部现象与宏观材料行为联系起来，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.