Kristallogrpahie & Geomaterialforschung

Supervisors: Prof. Ella M. Schmidt/ Dr. Paul Klar

This project focuses on investigating aluminium phosphate (AlPO4) framework materials, particularly AlPO4-5 and AlPO4-11. These zeotype materials with trivalent and pentavalent cations are composed of interconnected tetrahedral units that form microporous structures, enabling important applications such as molecular sieving. At the same time, these structures exhibit significant flexibility, as the networks can easily undergo distortions. These structural distortions are very subtle disturbances of the ideal structure, but despite the small amplitude, their influence on macroscopic properties and hence applied aspects of the materials should not be underestimated. The key objective is to explore how this flexibility - driven by rigid unit modes (RUMs), which are zero- or low-energy structural distortions - changes with temperature, heteroatom substitution of network sites, and guest molecules in the pores. By employing advanced materials characterization techniques such as single-crystal diffuse X-ray scattering, the project aims to identify how and when these flexible distortions transform into ordered, modulated structures. Understanding this dynamic behaviour from a fundamental perspective will provide insights into how such materials can be engineered in the future for applications in catalysis, gas separation, and other areas where tailored porous materials are essential.

The solid solution series of Olivine (Fe_xMg_1-x)₂SiO₄ (0 < x < 1) and compounds with olivine structure are considered as a natural CO₂ storage material, a source of alkalinity during enhanced weathering and as a potential cathode material. Olivine with a composition of Fe_0.1Mg_0.9SiO₄ is the dominant phase of the upper mantle and one of the most abundant minerals on Earth. Members of the mineral group are present in igne-ous and metamorphic rocks of basaltic origin and a common constituent of chondritic and achon-dritic meteorites.
In the crystal structure, the divalent cations are distributed over two symmetrically independent octahedral layers. Additionally, 1/8 of the tetrahedral sites between the octahedra are occupied by Si⁴⁺. The overarching goal of this project is to understand possible local ordering principles in olivine and their relation to observable physical properties. It has been shown that different thermal hisotries of the sample material influence the cation partioning – an average structural propertie. However, we expect that correlations that presist only locally are much more sensitive to such envirnmental changes. Therefore, we aim at observing and manipulating different degrees of local order and use these as a more precice and probe of the sample history.