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University of Kiel The Faculties Faculty of Mathematics and
Natural Sciences Organizations Institute of Geosciences Crystallography
Research Profile The Team Projects Publications
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A choice of project summaries underlining the directions of research in the group Crystallography:
Current projects:
Completed projects
Crystallographic effects on microbial pyrite leaching
Projectleader: Prof. Dr. W. Depmeier
Grant: DFG
Time: since 2005
Dr. J. Toporski, Dr. A. Mutter, Dr. K. Etzel
 The relevance of microbial mineral leaching processes has resulted in a large number of studies by which microbial leaching of a wide variety of minerals by pure and mixed cultures of Bacteria and Archaea were experimentally examined. These lead to good understanding of biogeochemical processes that occur as effect of microbial metabolic activities.
The project described here aims to enhance our understanding of effects of parameters such as time, varied metabolism, direct or indirect leaching, and crystallographic orientation on microbial leaching of pyrite surfaces. Systematic assessment of highly characterized surfaces before and after exposure to the microbial cultures will result in quantification of the leaching processes. This will lead us to determine whether varied crystallographic orientation results in varied surface leaching features. The long-term goals of the study are to establish means that allow the controlled manipulation of pyrite and other metal sulfide surfaces.
We present issues related to possible effects of crystallographic orientation of pyrite surfaces on the leaching efficacy and resulting leaching surface features as a function of microbial activity. We devise microbial leaching experiments on pyrite surfaces of different orientation, including (100), (111) and (210). The experiments are performed using strains of mesophilic Bacteria and thermophilic Archaea. Six different microbial strains were tested initially, three mesophilic Bacteria (Thiobacillus sphaeroides, Acidithiobacillus ferrooxidans, Thiobacillus prosperus) and three thermophilic Archaea (Sulfolobus metallicus, Metallosphaera sedula, Sulfolobus spp.). In addition to the crystallographic orientation and nature of microbial species, parameters such as pH, temperature, and time may affect the leaching process. Epifluorescens microscopy observations show, that some microbial strains attach to the mineral surface whereas others remain planktonic in the liquid growth medium. Systematic studies addressing the effect of time are accomplished in time spans between one day and six weeks. Cell attachment commences after few days attaining a surface cell density that remains stable after approximately two weeks. Scanning Electron Microscopy (SEM) studies have shown that leaching effects become visible within few days of incubation. Surface alteration produces structures such as channels, inverse pyramids following crystallographic orientation, rectangular or round pits in the 10s to 100s um size range. Epifluorescens microscopy and SEM analysis has show that surface alteration as result of microbial activity occurs first at weaknesses in the surface, such as micro-scratches and possibly at crystallographic defects (e.g. screw and edge dislocations). Leaching occurs due to microbial activity, which results in lowering pH-values from 2.5 in the growth medium to approximately 1.5 in local micro-environments. To test whether microbial activity has a direct bearing on surface alteration, or whether abiotic acid leaching produces similar results, we devise experiments using sulfuric acid etching to compare features of surface alteration.
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Life Marker Chip development
Dr. J. Toporski
Following the successful MarsExpress
mission, Europe is gearing up for surface Mars exploration. The
ExoMars mission, currently scheduled to launch in 2011, will deliver a
rover to the surface of Mars that will be able to investigate the
Martian surface and shallow subsurface for its structure and
composition. A suite of complementary analytical instruments will
specifically engage on the search for organic substances, aiming to
characterize the habitability potential of the red planet or even
assess possible evidence of past or present habitation. The so called
Life Marker Chip (LMC) instrument is one of the instruments dedicated
to carry out this task. Employing biosensor concepts and
biotechnological approaches, this instruments is designed to recognize
complex organic substances. As part of an international team based in
the UK, The Netherlands, USA and Germany, we develop and test
instruments components in preparation for this challenging endeavor.
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BIOPAN flight opportunity
Dr. J. Toporski
Individual molecular and hardware components of the Life Marker
Chip instrument will be tested in a real space flight scenario, the
ESA BIOPAN flight opportunity. BIOPAN is a pan-like structure with a
bottom and lid plate that carries multiple experiment frame for
biological experiments under space conditions in low Earth
orbit. Launched on a Russian FOTON-M3 capsule it orbits Earth for
approximately two weeks, during which the BIOPAN opens and the
experiments are exposed to space conditions (microgravity, low
pressure, temperature, radiation,…). Our team (as above) will use this
opportunity in preparation of the Life Marker Chip instrument for
Space flight qualification.
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Al-rich microporous structures
Projectleader: Prof. Dr. W. Depmeier
Grant: DFG
Time: since 10/2002
Dr. L. Peters.
Dr. N.-S. Rahmoun.
 A commonly used rationale in the structural chemistry of aluminosilicates is known as Loewenstein'sche Rule (aluminium avoidance rule). The rule describes the fact that in structures of cornerconnected TO4 tetrahedra (T = Si, Al) direct linkages of AlO4 tetrahedra are energetically unfavourable and hence avoided. For ratios Al:Si = 1.0, this leads to an alternation of SiO4 and AlO4 tetrahedra in aluminosilicate structures. This rule particularly holds for framework silicates of general framework composition [AlxSi1-xO2]x- and is very popular, e.g., in the Zeolite community. An additional characteristic of Al/Si-substitution series in aluminosilicate structures is their remarkable asymmetry: While aluminosilicates with 0 ≤ Al:Si ≤ 1 are very common and can be found in huge, geologically relevant amounts, those with 1 < Al:Si ≤ ∞ are very, very rare. This particularly holds for structures which contain one topologically distinct type of tetrahedra, only. In this project, we aim at obtaining reproducible preparation "recipes" for such phases. Subsequently they should be characterised with modern analytical techniques, to gather information about their structures and properties. Possibilities for the preparation of different Al-rich microporous structures should be explored. Peters, L., Knorr, K., Knapp, M., and Depmeier, W. (2005) Thermal expansion of gehlenite, Ca2Al[AlSiO7], and the related aluminates (LnCa)Al[AlSiO7], Ln: Tb, Sm. Physics and Chemistry of Minerals, 32, 460-465.
Peters, L., Knorr, K., Schmid-Beurmann, P., and Depmeier, W. (2006) On the volume of solid solutions: An anisotropic approach. Physics and Chemistry of Minerals, in print.
Peters, L., Knorr, K., and Depmeier, W. (2006) Structural Variation in the Solid-Solution Series (LnxCa2-x)Al[Al1+xSi1-xO7] with 0<1 and Ln: La, Eu, Er. Zeitschrift für Anorganische und Allgemeine Chemie, 632, p. 301-306.>
Peters, L., Knorr, K., Katzke, H., Knapp, M., and Depmeier, W. (2006) The transformation mechanism of the sodalite to melilite-topology: Thermal expansion and decomposition of bicchulite to melilite-type compounds. Zeitschrift für Kristallographie, 221(3), in print.
Peters, L., Knorr, K., Fechtelkord, M., Appel, P., and Depmeier, W. (2006) Structural variations in the solid solution series of sodalite-type |(EuxCa2-x)4(OH)8|[(Al2+xSi1-x)4O24]-SOD with 0<1, determined by X-ray powder diffraction and 27Al MAS NMR spectroscopy. Zeitschrift für Kristallographie, submitted.>
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Anion substitution in sodalites
Projectleader: Prof. Dr. W. Depmeier
Grant: DFG, Special Program "Substitutionsmischkristalle"
Time: since 11.2002
Greys Vega Flores, M.Sc.,
Aim of this project is to study the influence of an anion subsitution in selected examples of the sodalite structure type on their structure, phase transitions, phase diagrams and selected properties.
The examinations should contribute to the knowledge of the influence of this cage-guest anion substitution on on the complex competitive interactions between framework and guest anions, framework and guest cations, and guest anions and cations.
Their impact on the formation of (ordered) modulated or statistically disordered phases is to be analysed.
The compressibilities of selected aluminosilicate sodalites as a function of their state of loading shall be probed using high-pressure diffraction.
The critical concentration at which the framework starts to collapse under pressure is to be determined.
Thermal expansion of some sodalites containing large cage cations shows a discontinuity with respect to temperature.
The reason for this is not clear yet and still a matter of debate. Experiments at higher pressures should enable us to support or discard some of the differing suggestions.
- Depmeier, W.: The Sodalite Family - A Simple Architecture, but
Versatile Framework Structure. In: G. Ferraris & St. Merlino (eds.):
Micro- and Mesoporous Mineral Phases, Washington, Reviews in
Mineralogy and Geochemistry Vol. 57, 203 - 240 (2005)
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CarbidoNitrido
Project leader:
Prof. Dr. B. Winkler, Frankfurt,
Prof. Dr. W. Schnick, München,
PD. Dr. K. Knorr
Grant: DFG, Special program "Substitutionsmischkristalle"
Time: since 11.2002
Dr. A. Friedrich (2002-2005),
Dipl. Chem. A. Lieb (2002-2006),
Dr. E. Juarez seit 2005,
Nitridosilicates and Oxonitridosilicates (Siones) can be thougth of as a subclass
of Oxonitridoalumosilicates (Sialones), in which nitrogen atoms are partially substituted for by oxygen
and tetrahedra-centres (Si) by Al. There are several examples for this class of materials which allow for a considerable amount of cation and anion substitutions of this type.
Using exemplary nitridosilicates, oxonitridosilicates and oxonitridoaluminosilicates, factors should be identified which bias the aimed synthesis of these materials.
In addition, limits for the miscibility should be determined such that controlled synthesis of materials with a defined composition becomes possible.
In parallel, the influence of cation- and anion-substitution on selcted physical properties, in particular
mechanical and optical properties, are investigated quantitatively. Since pressure induced structural variations are typically much larger then those induced by "chemical pressure"
, i.e. internal pressure caused by substitutions of atoms / structural units with varying spatial requirements, in-situ high-pressure investigations are envisioned to complement the substitutional work.
Aside from pressure- and temperature dependent in-situ investigations, parameter-free quantummechanical calculations regarding structure-property realtionships in nitridosilicates, oxonitridosilicates and oxonitridoaluminosilicates are planned.
Determination of bond-strengths and -types, elastic poperties and structural variations in dependence on composition and pressure will allow for a deeper insight
into substitution effects in this class of materials. This will mark a crucial step forward regarding aimed syntheses of materials with "tailored" properties.
Basis for these investigations are the project leaders' significant contributions towards preparation of nitridosilicates, oxonitridosilicates and oxonitridoaluminosilicates.
The established synthesis methods should be instrumentally and methodically improved. For this purpose, time-resolved experiments are envisioned, and the Kiel-Berlin-cell and a newly developed resistance-furnace will be used
- Friedrich, A., Haussühl, E., Morgenroth, W., Lieb, A., Winkler,
B., Knorr, K., and Schnick, W. (2006) Crystal structure of the
high-pressure phase of the oxonitridosilicate chloride
Ce4[Si4O3+xN7-x]Cl1-xOx, x=0.2. Acta Crystallogr. B, 62(2) 205-211.
- Juarez-Arellano, E.A., Friedrich, A., Knorr, K., Lieb, A.,
Winkler, B., Amboage, M., Hanfland, M., and Schnick, W. (2006)
Compressibility of the nitridosilicate SrYb[Si4N7] and the
oxonitridoaluminosilicates MYb[Si4-x]AlxOxN7-x (x=2, M=Sr, Ba). Acta
Crystallographica B, in print.
- Friedrich, A., Knorr, K.,
Lieb, A., Rath, S., Hanfland, M., Winkler, B., and Schnick, W. (2005)
Bulk modulus and phase transition of the oxonitridosilicate chloride
Ce4[Si4O3+xN7-x]Cl1-xOx, x = 0.2 at high pressures up to 28 GPa
Zeitschrift für Kristallographie, 220(2,3), 245-249.
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Instrumentation at PETRA III
Project leader PD. Dr. K. Knorr
Time: since 2004
Coordination of a grant proposal for construction of a beamline for experiments at extreme conditions (p
Mbar, T > 2000 K)
New opportunities for science under extreme conditions are
becoming possible through the PETRA III storage ring at DESY, Hamburg,
which will undergo a major upgrade starting in 2007. As a result,
there will be a 3rd generation synchrotron available in Germany, that
will be comparable to or even superior to the current facilities at
the ESRF.
High brilliance hard X-rays are essential for diffraction
experiments at extreme conditions in order to penetrate various kinds
of sample containment (diamond anvil cells (DAC), large volume
Paris/Edinburgh-type cells, furnaces and cryostats). In order to
achieve ultra-high pressures in the Mbar regime, micrometer sized
samples (about 10 microns) are required. At routinely accessible pressures (to
50 GPa) such a spot size allows higher resolution since a sample
volume in the pressure cell having smaller pressure and/or temperature
gradients can be investigated. Studies with monochromatic X-rays go
beyond simple phase and cell-parameter determination by measurements
of reliable diffraction intensities being the prerequisite for
solution and refinement of complex crystal structure at extreme
conditions. A high signal/noise ratio is mandatory for the measurement
of low-Z materials and the analysis of slight structural distortions,
which manifest themselves in small intensity changes, weak
superstructure reflections etc. All this is only possible at 3rd
generation synchrotron sources.
The installation of a high-energy micro focus experiment dedicated
to X-ray diffraction at extreme conditions is proposed for
PETRA-III. These extreme conditions include simultaneously pressures
from ambient to the megabar range and temperatures ranging from 4 to
above 2500 K.
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Uranium compounds
Project Leaders: Prof. Dr. W. Depmeier, PD. Dr. H. Katzke, Prof. Dr. S. Krivovichev, St. Petersburg, Moscow
Grant: DFG, DAAD
Time: since 2005
Dr. Evgeny Alekseev, Dipl. Min. Evgeny Nazarchuk
Text to come ...
- Krivovichev, S.V., Cahill, C.L., Nazarchuk, E.V., Burns, P.C., Armbruster, T. & Depmeier, W.: Chiral open-framework uranyl molybdates. 1. Topological diversity: synthesis and crystal structure of [(C2H5)2NH2]2[(UO2)4(MoO4)5(H2O)](H2O). Microporous Mesoporous Materials 78, 209 - 215 (2005)
- Krivovichev, S.V., Burns, P.C., Armbruster, T., Nazarchuk, E.V. & Depmeier, W.: Chiral open- framework uranyl molybdates. 2. Flexibility of the U:Mo = 6:7 frameworks: syntheses and crystal structures of (UO2)0.82[C8H20N]0.36[(UO2)6(MoO4)7(H2O)2](H2O)n and [C6H14N2][(UO2)6(MoO4)7(H2O)2](H2O)m. Microporous Mesoporous Materials 78, 217 - 224 (2005)
- Krivovichev, S.V., Armbruster, T., Chernyshov, D. Yu., Burns, P.C., Nazarchuk, E.V. & Depmeier, W.: Chiral open-framework uranyl molybdates. 3. Synthesis, structure and the C2221 ? P212121 low-temperature phase transition of [C6H16N]2[(UO2)6(MoO4)7(H2O)2](H2O)2 Microporous Mesoporous Materials 78, 225 - 234 (2005)
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Determination of pore volumes, pore shapes and migration paths in microporous crystals
Prof. Dr. F. Liebau, Prof. Dr. H. Küppers, Prof. Dr. A.L. Spek, Utrecht, NL
 Volumes and shapes of pores are important characteristics with regard to syntheses and technical applications of zeolites and other microporous ma-terials. Present methods give only insufficient approximations of pore vol-umes, pore shapes and porosity.
In the present project Spek's existing program system PLATON, which contains an option SOLV that is primarily developed to study organic struc-tures, is extended for studies of crystalline microporous materials with inor-ganic host frameworks. The extended PLATON/SOLV program allows not only to determine, from crystal structure data, volumes and shapes of pores and the porosity of a material with high accuracy. It also determines the di-mensionality of each pore as function of the radius of a spherical guest atom or molecule, thus deciding whether the material is a clathrate or a zeoate with regard to this guest. In addition, diffusion paths for spherical guests of a given size can be determined and mapped.
So far we have applied the PLATON/SOLV program to several micro-porous materials, in particular to the zeolite afghanite (Fig). To demonstrate the potency of the program other microporous materials will be studied.
Atom valences and bond valences
Prof. Dr. F. Liebau, Prof. Dr. X. Wang, Houston, Texas, USA
 Based on the stoichiometry of normal valence compounds, each element is assigned one or several different atom valences. This stoichiometric valence (oxidation number) has positive or negative integer number values.
According to Pauling, the valence of an atom is distributed between the bonds to its neighbours. Provided that all neighbours of an atom are of the same element, the valence of a bond is the higher the shorter the bond. This is the basis of the well known bond valence model (BVM). For the majority of inorganic compounds, bond valence sums calculated with the BVM are within 0.1 valence units (v.u.) equal to the Values of the stoichiometric atom valences. However, our studies have shown that calculated bond valence sums for cations with one lone electron pair (LEP) deviate by up to 1.0 v.u. from their stoichiometric valences. These deviations are the larger the more distorted their coordination polyhedra, due to the stereochemical activity of the LEP. This suggests that, at least for cations with one LEP, bond valence sums calculated from crystal structure data are good approximations of a structural valence. The relationship between (positive and negative) stoichiometric and structural valence values is very similar to the relationship between ionisation energy and electron affinity on the one hand and electronegativity on the other. Future studies will have to prove whether this concept of two distinct valence properties can be extended to other atoms. Layered chalcogenides ResearchGroup
 The Crystallography Group in Kiel initiated and co-ordinated the interdisciplinary ResearchGroup on layered chalcogenides.
Project leader: Prof. Dr. W. Depmeier
Grant: DFG
Time: since 07.1999
Co-ordination of the DFG-RearchGroup on layered chalcogenides: „Wachstum und Grenzflächeneigenschaften von Sulfid- und Selenid-Schichtstrukturen“. Funding included a public relation post (Dr. Karin Griewatsch).
Chalcogenide-Misfit-Compounds: Preparation, structural characterisation, high-pressure- and computer-experiments.
Project leader: Prof. Dr. W. Depmeier
Grant: DFG
Time: since 07.1999
PD Dr. B. Winkler, Dr. M. Hytha, Dipl.-Min L. Ehm.
Selected representatives of misfit-compounds, general formula [(M1-yTyS)]1+x [(TS2)mTz] (M ist z.B. Sn, Pb, Bi, Sm, Gd, Ho; T = Ti, V, Cr, Nb, Ta; m = 1 - 3), were investigated, in accordance with the aims of the ResearchGroup. The interfaces between the layers and the cation-distribution were of special interest. Main experimental techniques were diffraction under high-pressure conditions and ab initio computer experiments.
[Translate to englisch:] Untersuchungen zur Synthese, Strukturen und strukturellen
Änderungen von Chalcophosphaten AIMIIPQ4 (Q =
S, Se)
Projektleitung: Prof. Drs. W. Depmeier; W. Bensch, Anorg. Chem. CAU
Förderung: DFG
Laufzeit: seit 17.09.2001
In Koop. mit: Prof. Dr. I. Belkyal, Dept. Chimie, Universite Cadi Ayyad, Marrakech.
In diesem Projekt sollen die Strukturen und eventuelle
Phasenumwandlungen der bei Raumbedingungen bekannten Thiophosphate KNiPS4
und KPdPS4 bei variablen Drücken und Temperaturen mit Hilfe von
Röntgenbeugung, spektroskopischen und thermoanalytischen Verfahren untersucht
werden. Diese Untersuchungen sollen durch Computerexperimente unterstützt und
ergänzt werden, wobei die modernsten uns zur Verfügung stehenden quantenmechanischen
ab initio Methoden zum Einsatz kommen sollen. An beiden Verbindungen sollen
auch Substitutions-, bzw. Interkalationsexperimente durchgeführt werden. Für
noch nicht bekannte Thiophosphate AIMIIPS4
(z.B. A = K, Rb; M = Sn, Pb, Zn, Cd) sollen Synthesewege erforscht und die
Produkte im Erfolgsfall wie oben charakterisiert werden. Eventuell anfallende
Thiophosphate anderer Stöchiometrie sollen zumindest strukturell aufgeklärt
werden. Zusätzlich sollen geeignete physikalische Eigenschaften, nicht zuletzt
im Hinblick auf eventuelle Anwendungsmöglichkeiten, gemessen werden. Die
binationale Kooperation soll dazu dienen, die marokkanischen
Kooperationspartner mit modernen festkörperanalytischen Methoden bekannt zu
machen. Die Installation eines Pulverdiffraktometers in Marrakech hat dort den
Keim für den Aufbau eines lokalen Kompetenzzentrums für Strukturaufklärung und
Phasenanalyse gelegt.
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[Translate to englisch:] Wirt/Gast-Wechselwirkungen in Bassanit: Labor- und
Computerexperimente
Projektleitung Prof. Dr. W. Depmeier, Prof. Dr. B. Winkler, Uni Frankfurt
Förderung: DFG
Laufzeit: beendet
Beteiligte Wissenschaftler: Dipl.-Min. H. Voigtländer
Trotz der großen technischen Bedeutung von
Calciumsulfat-Halbhydrat, CaSO4•0,5H2O, (Mineralname
Bassanit), sind Struktur und Dynamik der in die Kanäle (Ø ~ 4Å) der Struktur
eingebauten Wassermoleküle und ihre Wechselwirkung
mit der Wirtsstruktur (i.w. die Struktur des sogenannten γ-Anhydrits) noch
weitgehend unverstanden. Nach älteren Angaben liegt das Wasser geordnet und
durch schwache Wasserstoffbrücken an die Kanalwände gebunden vor. Eigene
neutronenspektroskopische Untersuchungen legen nahe, dass die Wassermoleküle
bei RT dynamisch fehlgeordnet sind; bei tiefen Temperaturen erfolgt ungeordnete
Kondensation an den Kanalwänden. Die Hydratation und Dehydratation verlaufen
ähnlich wie in Zeolithen. Fragen zu Existenz und Eigenschaften von Subhydraten
sind noch weitgehend ungeklärt. Hohe Drücke sollten die Wechselwirkungen
zwischen Wirt und Gästen in den Verbindungen CaSO4·xH2O
verstärken.
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[Translate to englisch:] Realbau von Mineralen und anderen Festkörpern
Projektleiter: Prof. Dr. M. Czank
In Koop. mit: Prof. Dr. A.G. Castellanos-Guzman, Laboratorio
de investigacion en materiales, Uni Gaudalajara, Mexiko; Prof. Dr. F. Faupel,
Techn. Fak., CAU, Kiel; Dr. K.
Friese, Dep. Física Materia Condensada, Uni Pais Vasco, Bilbao, Spanien; Dr. M. Pósfai, Dept. Earth &
Environm. Sci., Uni Veszprém, Ungarn; Dr. G. Simon, Min. Staatssammlg.,
München; Prof. Dr. G. van Tendeloo, EMAT,
Uni Antwerpen, Belgium.
In den Arbeiten wurde vor allem die
Transmissionselektronenmikroskopie zur Bestimmung und Charakterisierung des
Realbaus von Mineralen und synthetischen Festkörpern eingesetzt:
- Bestimmung und
Charakterisierung der Realbau: Die Kenntnis des Realbaus (z.B.:
Baufehler, incommensurable Modulationen, Domänenstruktur) von Mineralen und
synthetischen Festkörpern ermöglicht Rückschlüsse auf deren Entstehung- bzw.
Synthesebedingungen.
- In-situ
temperaturabhängige TEM-Untersuchungen: Phasenumwandlungen sowie
Änderungen im Realbau werden unter direkter Beobachtung, vornämlich durch
Elektronenbeugung, zwischen 100K und 1100K verfolgt.
- „Elektronen-Kristallographie“ von Meso- und Nanokristallen: Bestimmung der
kristallographischen Daten (Elementarzelle, Raumgruppe, wenn möglich auch
Atomlagen) von äußerst kleinen Kristalliten, die mit anderen Methoden nicht
zugänglich sind.
- Aktuelle Untersuchungen
- „Amphiboloide“: eine neue
homologe strukturelle Reihe mit den Endgliedern Amphibole und Howieite.
- Cancrinite: inkommensurable Überstruktur.
- Charoite: Strukturbestimmung
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[Translate to englisch:] Struktur-Eigenschaftsbeziehungen und Hochdruckpolymorphie von
Fluoriden
Projektleitung: Prof. Dr. Björn Winkler, Uni Frankfurt, Dr. K. Knorr
Förderung: DFG
Laufzeit: 2000-2002
Beteiligte Wissenschaftler: A. Dubinin
[Translate to englisch:] In strukturell einfachen Difluoriden können die Kationen über einen sehr weiten Konzentrationsbereich (bis zu 30 mol%) substituiert werden, während F-Ionen auf Zwischengitterplätzen eingebaut werden können. Ziel der Arbeiten ist es, die Änderungen der makroskopischen Eigenschaften zu quantifizieren und zu verstehen. Dazu sollen quantenmechanische Modelle eingesetzt werden, um die Struktur-Eigenschaftsbeziehungen von Idealkristallen zu bestimmen. Diese Ergebnisse sollen dann mit experimentellen in situ Hochdruck- und Hochtemperatur-Beugungsuntersuchungen an Realkristallen verglichen werden, um so die induzierten Änderungen zu verstehen.
[Translate to englisch:]
- Dubinin, A., Winkler, B., Knorr, K., and Milman, V. (2004) Lattice
dynamics and elastic properties of PbF2 and BaF2 from
quantum mechanical calculations. European Physical Journal B, 39, 27-33.
- Ehm, L., Knorr, K., Mädler, F., Voigtländer, H.,
Busetto, E., Cassetta, A., Lausi, A., and Winkler, B. (2003)
High-Pressure X-ray diffraction study on alpha-PbF2. J. Phys. Chem.
Sol., 64, p. 919-925.
- Winkler, B., Knorr, K., and Milman, V. (2003) Prediction of the
structure of LaF3 at high pressures. Journal of Alloys and Compounds,
349, 111-113.
- Diploma thesis: L. Peters (2002) Thermogravimetrische und roentgenographische Untersuchungen an LaF3 zwischen Raumtemperatur und 1273 K.
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[Translate to englisch:] Struktur-Eigenschaftsbeziehungen von
Übergangsmetallphosphiden,-carbiden und -nitriden
Projektleitung: Prof. Dr. Björn Winkler, Uni Frankfurt, Dr. K. Knorr
Förderung: DFG, BMZ
Laufzeit: 2001-2004
In Koop. mit: Prof. Dr. M. Avalos Borja, UNAM, Ensenada, Mexiko.
Beteiligte Wissenschaftler: V. Soto, M.Sc.; L. Lopez de la
Torre, M.Sc.
[Translate to englisch:] Struktur-Eigenschaftsbeziehungen von Phasen, die bei der katalytischen Entschwefelung von Erdöl eine Rolle spielen, sollen mit einer Kombination von quantenmechanischen Rechnungen, in situ Röntgenhochdruckuntersuchungen und Elektronen-Energie-Verlust-Spektroskopie untersucht werden. Konkret sollen hier Übergangsmetall-Carbide, -Phosphide und -Nitride untersucht werden, die als Nebenprodukte bei der, auf der Reaktion mit Sulfiden beruhenden, konventionellen, katalytischen Entschwefelung entstehen. Ziel der Untersuchungen ist es, ein tieferes Verständnis der interatomaren Wechselwirkungen in diesen strukturell und chemisch einfachen Phasen zu erreichen. Dies soll die Grundlage für ein besseres Verständnis ihrer katalytischen Eigenschaften liefern, und so die Verbesserung von Katalysatoren ermöglichen.
[Translate to englisch:]
- Lopez de la Torre, L., Winkler, B., Schreuer, J., Knorr, K., and
Avalos-Borja, M. (2005) Elastic Properties of tantalum carbide, TaC. Solid State
Communications, 134, 245-250.
- Soto, V., Knorr, K., Ehm, L., Baehtz, C., Winkler, B., and
Avalos-Borja, M. (2004) High-pressure and high-temperature powder diffraction on
molybdenum diphosphide, MoP2. Zeitschrift für Kristallographie, 219,
p. 309-313.
- Winkler, B., Knorr, K., Hytha, M., Milman, V., Soto,
V., and Avalos, M. (2003) Crystal chemistry of molybdenum phosphides from
density functional theory calculations. Journal of Physics and Chemistry of
Solids, 64, 405-411.
- Ph.D. thesis: V. Soto (2004) CICESE, Ensenada, Mexico; L. Lopez de la Torre (2006) CICESE, Ensenada, Mexico.
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[Translate to englisch:] Struktur-Eigenschaftsbeziehungen von Protonenleitern des Typs
MHXO4 und M3H(XO4)2
Projektleitung Dr. K. Knorr, Prof. Dr. W. Depmeier
Förderung: DFG
Laufzeit: seit 02.2001
Beteiligte Wissenschaftler: G. Lentz
 [Translate to englisch:] Die Kristallstrukturen und die Dynamik von ausgewählten Vertretern der protonenleitenden Substanzklassen mit den allgemeinen Formeln MHXO4 und M3H(XO4)2 (M: Alkalimetallkationen oder Ammonium, X: Se, S) sollen untersucht werden. Mittels Hochdruck/ Hochtemperatur-Röntgen- und Neutronenbeugung soll der Einfluss interatomarer Abstände auf die strukturellen Mechanismen der Protonenleitung untersucht werden. Es sollen die Protonenleitungspfade mit Fourier- und Maximum-Entropie-Methoden aus Beugungsdaten rekonstruiert und deren Geometrie sowie Änderungen der Geometrie in Abhängigkeit von Druck und Temperatur analysiert werden. Die Probenauswahl konzentriert sich zunächst auf Kalium- und Ammoniumverbindungen bei welchen, auf Grund der speziellen Werte der Ionenradien, das Vorliegen kritischer Abstände, die für den Übergang zu guter Protonenleitung verantwortlich sein sollen, vermutet wird. Weiterhin soll durch den Vergleich der Kalium- und Ammoniumverbindungen der etwaige Beitrag der Protonen der Ammoniumgruppe zur Protonenleitung studiert werden. Der Einfluss von Voll- und Teildeuterierung auf Strukturen, Phasensequenzen, Umwandlungscharakteristika etc. ist zu studieren. Neben der kristallographischen Charakterisierung ist ein weiterer Schwerpunkt die Untersuchung des Einflusses struktureller Änderungen, welche durch die Variation von Druck und Temperatur hervorgerufen werden, auf physikalisch/ chemische Eigenschaften und die Dynamik.
[Translate to englisch:]
- Bagdassarov, N., Lentz, G.Y. (2005) High pressure behaviour of KHSO4 studied by electrical impedance spectroscopy. Solid State Communications 136, 16-21.
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