Transition metal oxides with low dimensional interactions

The close relationship between the crystal structure and the pysical properties (electric conductivity, magnetism) of a compound is a well known and characteristic aspect of electronically low dimensional systems. Such (quasi) 1D systems are the task of intense research especially in solid state physics, as new aspects for the description of super-conductivity (conduction of electric energy without resistance) in low - doped high - temperature superconducters are to be expected. The proposed project deals with a thoroughful detailed structural charaeterisation of such electronically and structurally low dimensional compounds, primarily with X-ray diffraction an single crystals. The combination with spectroscopic methods (Mössbauer-, Raman, Infrared spectroscopy) will allow a comparison between average and local structural properties of the compounds under investigation. The compounds, necessary for the planned investigations, will be synthesised in the laboratory at high temperature (up to 1500C) and high pressure (up to 3 GPa). For the investigations, two classes of compounds have been selected, which can be derived from mineral groups with high relevance in geoscience. These substance classes are (i) the clinopyroxenes, ABSi206, where Si 4 + is replaced by Ge` and (ii) the brownmillerite family A2B20 5 . Thought their high relevance in solid state research and material science, there is a distinct lack of exact structural data, especially at elevated temperatures. However, it is the knowledge of exact structural data, which is of fundamental importance for e.g. any theoretical treatment of there systems. The central point of interest in the proposed project is the detailed investigation of the variation of the crystal structure and the physical properties (magnetism) of the compounds in question within the parameter field: "chemical composition" - "temperature". Therefore measurements will be performed in-situ and the measuring temperatures will be varied between -200C and 900C. Also the chemical composition of the samples will be varied by the focused exchange of elements an orte or several lattice sites. It will be investigated, if and in which way the atomic arrangement (crystal structure) of the compound reacts to the altered extrinsic (temperature) and intrinsic circumstands and what will happen in detail at the phase transitions, expected.