Conference Schedule

Day1: June 4, 2018

Keynote Forum

Biography

Werner Paulus is exploring low temperature oxygen diffusion mechanisms in transition metal oxides. Oxygen doping, via topotactic reaction mechanisms while proceeding at ambient temperature is a powerful tool to access structural and electronic complexity in a controlled way. It also allows to better explore the underlying diffusion mechanisms on an atomic scale, having huge importance in solid state ionics, e.g. for the optimisation of battery materials, fuel cell membranes/electrolytes or sensors. Research activities cover synthesis methods from powder to large single crystals and to explore oxygen intercalation reactions in especially dedicated electrochemical cells on single crystals and polycrystalline electrodes by neutron and X-ray diffraction (synchrotron & laboratory), spectroscopy (XAFS, Raman, INS, IXS, NMR) combined with 18O/16O oxygen isotope exchange reactions and sophisticated data analysis (Maximum Entropy, twinning).

 


Abstract

Transition Metal Oxides with strongly correlated electrons have been studied intensively due their interesting physical properties. This includes colossal magnetoresistance (CMR) where huge variations in resistance are achieved just by small changes in the applied magnetic field, or high temperature superconductivity (HTC) to name two of them [3-6]. These materials are characterized by the existence of several competing states such as charge, spin and orbital ordering, interacting in a synergetic way and leading to fairly complex phase diagrams. Thereby the physical properties can be tuned in a wide range via hole doping, e.g. by cation substitution as is the case for RE2-xSrxMO4.

An alternative way of hole doping presents oxygen intercalation, generally proceeding at ambient temperature via a topotactic oxygen uptake along shallow potential diffusion pathways. Contrary to the cation substitution, requiring high reaction temperatures, oxygen intercalation reactions allow the controlled synthesis of strongly correlated oxides far away from thermodynamic equilibrium, essentially resulting in kinetically stabilized and thus metastable phases.

Low temperature reactivity of solids may thus be used as a concept, to investigate the limits of available structural and electronic complexity in transition metal oxides. The reaction pathway to insert oxygen at low temperatures in solid oxides becomes a decisive parameter to tune correlations, leading to extremely complex phase relations as physical and structural properties are not only depending on the overall stoichiometry, but decisively on the sample history. Taking these oxides as oxygen ‘sponges’ operating at low reaction temperatures down to ambient, structural and electronic correlation lengths could then be influenced by the reaction conditions and kinetics. We here discuss here the challenges, low temperature solid state reactivity implies for the synthesis of new complex oxides but equally the current understanding of the relying oxygen diffusion mechanisms, having a huge fundamental and technological interest.

 

Biography

Professor Mingxing Zhang has his expertise in crystallography of phase transformations in solids and crystallography of grain refinement of cast metals.  His research focuses on development of new metallic materials and their processing in order to improve the properties of the alloys.  He is also an expert on surface engineering of engineering metallic materials. He is one of the two inventors of the well-known edge-to-edge matching model and proposes the research theme on crystallography of grain refinement for cast metals.  He is currently a professor in materials science and engineering in the School of Mechanical and Mining Engineering, the University of Queensland. (orcid.org/0000-0001-8363-6968)


Abstract

Properties of materials are governed by their microstructures, which in turn are controlled by the phase transformations at a given composition. To obtain the desired microstructure, it is essential to understand the phase transformations that occur in the material. Crystallography of phase transformations defines the morphology of microstructures, explains the actual phase transformation process at an atomic level and describes the relationship between the new phase and the parent phase.  Hence, the crystallography controls the final properties of materials.  In the past decades, although a number of theories/models have been developed to understand the crystallography of phase transformations, none of them can be used to design new materials and processes until the edge-to-edge matching (E2EM) model became available [1].

Development of the E2EM model was based on the principles that the nature of a coherent or semi-coherent interface and the associated crystallographic relationships are governed by minimisation of interfacial energy between two crystals; and that the necessary and sufficient condition for minimisation of the interfacial energy is to maximize the atom matching. The best and most effective approach to achieve the maximum atom matching is the matching of atom rows that are close packed or nearly close packed and are contained in the matching planes that are arranged to meet in the “edge to edge” manner as shown in following figure.

Major advantage of the E2EM model over all other previous models is its predictive capacity from the first principle.  Thus, it can be used to design new alloys and processes.  In this presentation, after briefly reviewing the success of this model in predictions of the crystallographic features of diffusion controlled phase transformations in solids [1], its applications in development of new and more effective grain refiners for cast metals, including magnesium alloys [2], zinc alloys [3] and steels [4], are introduced.  Predictions of the textures and growth features of epitaxial growth and crystalline nanowires [5] are also presented.

 

Biography

Dr. Martin Meven received his PhD in natural sciences at the Institute of Crystallography at RWTH Aachen University in 2001. Aside from his scientific work on HT superconductors during this time he gained experience in scattering methods with X-ray diffractometry including instrument development. He extended his expertise as postdoc at Munich, where he developed a new single crystal diffractometer for hot neutrons at the neutron source FRM II of the Heinz Maier-Leibnitz Zentrum (MLZ) in Garching, Germany. Since then he has been working as instrument scientist on various topics in the fields of crystallography, solid state chemistry and solid matter physics and material sciences. He has served as a board member of various scientific conferences and scientific referee at review panels at various neutron sources in Europe. He is the speaker of the Special Interest Group on Neutron Scattering (SG # 7) of the German Society of Crystallography (DGK) and organizes workshops on neutron scattering techniques for crystallographers to young scientists on a regular basis. (orcid.org/0000-0002-8079-5848)


Abstract

The unique features of Neutrons make them a valuable tool for many crystallographic studies on hot topics in physics, chemistry, biology and material sciences. Their interaction with nuclei yields not only high penetration depths but also interaction strengths that differ significantly from the those well known for X-rays, e.g. some light elements (H, O) show relative large scattering cross sections compared to many heavy elements while neighbored elements can differ strongly.

Therefore, Neutron imaging can be used to perform in situ radiography of engines to study the different moving parts and liquids involved in its operation. In the area of energy applications are the non-destructive spacial reconstruction of the distribution of elements inside new battery types during charge-discharge-cycles. This can be combined with neutron diffraction studies on the underlying chemical processes to develop new materials, e.g. for Li-ion or sodium metal halide batteries [1, 2]. The sensitivity of neutrons for light elements plays also an important role, e.g. for the understanding of energy relevant compounds like ionic conductors based on layered perovskites [3]. This holds true also for for detailed studies on complex H bonds in minerals (phosphates, silicates, etc.) or organic matter/biological systems in life sciences, e.g. antibiotics [4]. The magnetic moment of neutrons allows detailed insights into magnetic order and related phase transitions. This feature is widely used in recent studies on multiferroics but also on modern high temperature superconductors based on cuprates [5] or iron arsenides [6] and played also an important role in the discovery of skyrmions [7].

The successful contribution of neutrons to various scientific applications has been made possible by advances in methods and instrumentation at existing neutron sources (e.g. in Europe ILL, MLZ, ISIS, etc.) in recent years. This and the installation of the new European Spallation Source ESS will support this trend also for the future.

Tracks

  • Chemical Crystallography | Advanced Crystallography | Crystal Growth | Nuclear Magnetic Resonance Crystallography | Advances in Neutron Diffraction | Biological Structure Determination | Application of Modern Chemistry
Location: Bleriot- 2

Henrich H. Paradies

Jacobs-University, Germany

Chair

Vijeesh Padmanabhan

The Cochin College, India

Co Chair