Metastability and crystallisation of metamict minerals

点击翻译按钮获取中文摘要

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.