Mechanochemistry of Oxide and Fluoride Nonequilibrium Phases: Mechanosynthesis, Solid State Kinetics and Spectroscopic Properties

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The project deals with the directed mechanochemical synthesis and structural characterization of new crystalline oxide and fluoride non-equilibrium phases. While in the first period mainly systems crystallizing with the perovskite, olivine, garnet, fluorite, and spinel structure were investigated, in the second period, the research will be extended to more complex materials such as (i) oxides with the mullite-type structure with general composition Bi2X4O9/10 (X = Ga3+, Fe3+, Al3+, Mn3+, Mn4+), (ii) the pyroxene-type compounds, e. g., Li-containing pyroxenes LiYSi2O6 (Y = Fe3+, Al3+, Cr3+), and (iii) the Li2ZSiO4 family of oxides (Z = Fe2+, Mn2+, Co2+, Ni2+). Also other fluoride systems like BaSnF4, BaMgF4, and metastable composites based on SnF2 will be investigated. Complex problems regarding the metastable structural configurations in several systems investigated in the first period will be processed in cooperation with theoretically-oriented groups.The main focus will be given to the investigation of the mechanisms and kinetics of the formation of metastable compounds involving studies concerning their thermal stability, especially their local atomic and electronic structures. Primarily, complementary nuclear methods such as NMR- and Mössbauer spectroscopy will be used, which allow to follow the relaxation paths of the as-prepared phases to the equilibrium state and associated kinetics at the local scale. Besides the determination of the local structure of the non-equilibrium phases the investigation of the dynamic, electric and magnetic properties is the second priority of the project. The project shall contribute to an understanding of the structure-forming factors which govern the formation mechanisms of the mechanosynthesized non-equilibrium phases, in order to manipulate them in a directed way for the synthesis of new functional materials.