The article describes Permian metapegmatite garnets from the Koralpe region (Eastern Alps, Austria) that contain abundant submicrometer- to micrometer-sized inclusions of rutile, corundum, Fe-Mn phosphate, ilmenite, xenotime, zircon, and apatite. Variations in the inclusion abundance, phase assemblage, habit, and size define sector and concentric zones in garnets, tracing low-indexed garnet facets. Zoning resulted from a process occurring at the garnet-melt interface, homogeneous along each facet, but sensitive to its crystallographic plane. Oriented interface nucleation seems to better explain the fact that the frequency of rutile-garnet CORs varies strongly not only between cores and rims but also between garnet core domains. Their formation explains observations commonly attributed to exsolution, making distinguishing between these two mechanisms a challenge. We suggest interface-dependence of SPOs and COR frequencies as criteria for identifying inclusion formation via oriented nucleation. The article is written based on past results and gives important guidelines for investigations in this project.
COBISS.SI-ID: 0000000
Today, ab-initio calculations are becoming a powerful tool to perform virtual experiments that have capacity to predict and to reproduce experimentally observed non-periodic features, such as interfaces, that are responsible for quantum properties of materials. In our paper we investigate 2D quantum-well structures, known as inversion boundaries (IB). Combining atomistic modeling, DFT calculations and HRTEM analysis we provide a fundamental insight into the structure and stability of Sb-rich basal-plane IBs in ZnO. DFT screening for potential IB model was based on stacking deviations in originating wurtzite structure. The key to the stability of IB structures has been found to lie in their cationic stacking. We show that the energies of constituting stacking segments can be used to predict new IB structures without the need of further ab-initio calculations. DFT optimized models of IBs accurately predict the experimentally observed IB structures with lateral relaxations down to a precision of ~1 pm. The refined structures will help to solve open questions related to their role in electron transport, phonon scattering, p-type conductivity, affinity of dopants to generate IBs and the underlying formation mechanisms, whereas the excellent match between the calculations and experiment demonstrated in our study opens new perspectives for prediction of such properties from first principles. The article is not directly related to the research topic of this project but gives important guideline in studying the origin of interfaces in garnets.
COBISS.SI-ID: 26023939