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PD Dr. Tom Nilges
WWU Münster
Institut für Anorganische
und Analytische Chemie
Corrensstraße 30
D-48149 Münster
Phone:
+49 (251) 83-36645
Fax:
+49 (251) 83-36002
e-mail:
nilges at
uni-muenster dot de
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Today ion conductors play a key role in high-technology devices like solid state batteries,
chemical sensors, solar cells or solid oxide fuel cells. Within the
SFB 458 "Ionenbewegung in
Materialien mit ungeordneten Strukturen- vom Elementarschritt zum makroskopischen Transport" the
development of ion conducting materials and the understanding of the transport phenomena of these
materials are of great interest. We focus our research activities on the synthesis and characterisation
of new ion conducting copper, silver and lithium compounds as well as the optimisation of present
ion conducting materials by chemical modification of the non mobile part of the structures. A wide
range of analytic, spectroscopic and diffraction methods will be applied to the materials in order to
get a detailed insight in the chemical and physical properties. Starting with the crystal structure
determination and the determination of the electrical properties we try to optimise the materials in
terms of long time stability, conductivity and polymorphism. Various methods like DSC (Differential
scanning calorimetry), DTA (Differential thermal analysis) are used to get detailed information about
the thermal properties. Spectroscopic methods like IR and Raman spectroscopy and solid state NMR
techniques are additional applications to support the optimisation process.
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| Thermoelectrics and Energy Materials |
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The discovery of the new class of coinage metal polychalcogenide halides uncovered a new set of materials
with promising properties. An extremely low thermal diffusivity in combination with high mobility and
redox activity of structure units in the solid state are common features of this compounds. A linear and
mobile chalcogen chain is responsible for a reversible switching of the electric properties from a p-conducting
via an n-conducting state back to p-conduction by a simple change of temperature in one compound. Such a
reversible redox-reaction (formation and breaking of covalently-bonded Te dumbells) within the chalcogenide
substructure can have a certain impact in data storage applications due to its local resistivity switch in
the sub-nano regime. The high mobility of the coinage metal and the polychalcogenide substructure lead to an
highly efficient scattering of phonons and therefore an extremely low thermal diffusivity and thermal conductivity.
Some compounds reach the thermal conductivity of nanostructured materials and superlattices known to be the best
available thermoelectrics at the moment. Our activities will be focused on the optimization of the thermoelectric
properties to challenge the problems in energy production in the future. There are still major aspects in terms
of the efficiency and the stability of thermoelectrics, especially in bulk samples without nano-structuring,
which need to be solved soon.
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| Polymorphism and phase transitions |
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Polymorphism is a common feature in solid state ionics. It is of fundamental interest to learn something about the
formation, the stability and the kinetics of phases and their phase transitions. In cooperation with PD Dr. P. Schmidt,
TH Dresden, and Dr. R. Weihrich, University Regensburg, we will try to create a bottom up approach with the aid of
new synthesis strategies, the modulation of phase formation and growth and the examination of thermodynamics
and kinetics of crystal formation and crystal growth. We will focus on reactions via the gas phase and try to explain
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Recently we started to discover new semiconducting transition metal - main group polyphoshides.
Variations in the polyphosphide substructure from 0 dimensional molecular units, polymeric 1 dimensional
strands and 2 dimensional layers can be stabilized combining group 11 and group 14/15 elements.
New building units like M3Sn heteroclusters (M = Au) and the first inorganic material with
covalent Sb-P interactions have been prepared by main group halide mineralization reactions at elevated
temperatures. One key finding is the new and effective route to black phosphorus which makes this allotrope
now available for large scale applications. Due to their physical properties these polyphosphides are potential candidates for electrochemical
applications.
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| Non-harmonic refinements of crystal structures |
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In the scientific field of structure determination based on X-ray or neutron diffraction the refinement
of atomic positions using a non harmonic approach is a method to examine systems showing high dynamic
or static disorder. Disorder is a major aspect in the field of solid state ionics and is directly
connected to ion dynamics and transport phenomena in solid electrolytes. Based on the potential of
this method, like the calculation of joint probability density functions (jpdf) and one particle
potentials (opp), we try to get a better insight in the structural features of materials and their
physical properties. Directly connected to this method is the 3D - visualisation and analysis of the
jpdf data using modern visualization programs.
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| RE-T-Pnictide oxides (RE = Rare Earth metals; T = Transition metals) |
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Pnictide oxides of various compositions (ternary alkaline earth pnictide oxides,
quaternary rare earth - transition metal pnictide oxides and actinide - transition metal pnictide
oxides) have been structurally characterised. Those materials are build up from
alternating metal-oxide and metal-phosphide layers which are separated by metal
ions in some cases. Apart from the crystal structures the physical properties are only barely
characterised. In addition to the preparation of new materials we are interested in the determination
of the physical properties like magnetic susceptibility, Hall effect, electrical and
magneto resistivity and their optical and magnetooptical behaviour.
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