Research

Our research is focused on a broad range of theoretical and experimental inorganic materials chemistry, like the crystal structures and electronic states of main group metal cluster compounds, preparation and physical characterization of materials with unusual mixed metal oxidation states, density functional theory calculations of electronic structure of solid materials, surfaces and  small molecule crystals.

This includes the preparation and characterisation of novel tin and antimony cluster compounds with promising materials properties and the calculation of band structures of solid-state compounds to investigate the crystal structure and the electronic structure. For the preparation of these compounds, quite a number of different methods are employed, from classical high-temperature sintering in evacuated quartz tubes for the synthesis of pure powder materials to the crystallisation from metal melt, or gas-phase reactions (chemical transport reactions) for the preparation of single crystals. For the identification of these compounds, we use X-ray single crystal or powder diffraction, Mössbauer spectroscopy, electron spin resonance, energy dispersive X-ray spectrometry (EDX), high-resolution electron microscopy (HREM), transmission electron microscopy (TEM), measurements of the temperature dependence of the magnetic susceptibility and the electrical resistance.

This work involves a large number of national and international collaborations with research groups on the different topics in inorganic materials and theoretical chemistry.

The group has wide experience in using the state-of-the-art equipment at the Australian Nuclear Science and Technology Organisation (ANSTO) for powder and single-crystal neutron diffraction experiments and the Australian Synchrotron for powder diffraction and X-ray absorption experiments.

We also support the School of Chemical Sciences and external collaborators with solving and refining crystal structures on X-ray single crystal and powder diffraction data as part of the Auckland Science Analytical Services (ASAS).

SHare Facility Microcharacterisation, Faculty of Science

Projects

 

CRYSTAL STRUCTURE AND ELECTRONIC STRUCTURE OF MIXED MAIN GROUP METAL / TRANSITION METAL CLUSTER COMPOUNDS
The search for novel inorganic compounds with interesting electrical and magnetic properties is one of the most exciting areas of current solid-state materials chemistry. For example, the discovery of new high-temperature superconductors has lead to immense activity in solid-state chemistry and physics. In this context, the mixed main group metal – transition metal cluster compounds, which have not been studied extensively in the past, seem to be especially promising. This group of compounds form novel clusters with a wide variety of different combinations of metals and resulting architectures. The goal of this project is to discover new compounds by replacing the Sn-matrix of the known cluster compounds partially or completely by an Sb or Pb matrix and to prepare new pure and mixed Sn / Sb and Pb cluster compounds. The aim is to succeed in the formation of original condensed cluster compounds with a higher coordination number than six as it has been found only in the case of the Bi-cluster compounds. Here coordination numbers are realised up to the number of 12. Furthermore, we expect to synthesize new Sb-compounds in the unusual +2 similarly to the +1 oxidation state for Sn. Mössbauer spectroscopy is an excellent probe for the investigation of local phenomena such as oxidation states and the coordination sphere and has been proven as an extraordinary tool for the characterisation of Sn cluster compounds. Our research group is collaborating intensively with the Mössbauer group at the Technical University in Munich, one of the world-leading groups in this field.

CHEMICAL TRANSPORT OF TERNARY AND QUATERNARY Cu-Sb-OXIDES AND HALIDES WITH MIXED OXIDATION STATES
This project is in the field of solid-state materials and deals with the preparation and characterization of copper compounds with mixed Cu oxidation states. We were able to isolate the first compound in this series of new structure types, a new ternary Cu/Sb/Si – oxide containing a mixture of five Cu2+ atoms in different coordination spheres in one compound. This is a unique and very promising compound and could potentially be used for partial oxidation and reduction of copper similar to Cu-containing high-temperature superconductors. One of the most promising methods to produce such materials is by chemical transport, which is particularly useful for materials in reduced oxidation states. The goal is to prepare novel compounds with different compositions in order to study the influence of doping on electric and magnetic properties.

INFLUENCE OF RELATIVISTIC EFFECTS OF THE CRYSTAL STRUCTURE OF BINARY OXIDES AND HALIDES
Another research area is the investigation of the electronic properties of inorganic materials of transition group metals with unusual properties and structures. Relativistic effects have a significant influence on the properties of compounds containing heavy elements. They also have an enormous influence on the symmetry in the solid state. It was shown for the first time that group 11 halides exhibit large relativistic effects responsible for the formation of certain crystal structures. The chain-like structures which are realized in Gold(I)-halides, can be found in groups 11 and 12 oxides as well. To obtain a deeper insight of the electronic properties including the identification of the different oxidation states we like to carry out computer simulations of the electronic structure and chemical bonding in real space (ELF) using the solid-state density-functional programs.

BONDING SITUATION IN INCOMMENSURATELY MODULATED CRYSTAL STRUCTURES
Incommensurately modulated crystal structures show beside quasi-crystals the most complicated crystal structures in solid-state compounds. The loss of three-dimensional symmetry leads to special conditions in the electronic structures of these compounds. The theoretical description helps to understand the formation of the incommensurately modulated structures. Therefore, electronic structures of incommensurately modulated crystal structures have been investigated additionally.

SOME FURTHER PROJECTS
Of further interest are electric field gradients of heavy transition metals like Ru, Ir and Au, which are of particular interest for Mössbauer investigations. Density functional theory calculations of the isomer shifts and electric field gradients of Ru, Ir, Sn, Sb and Au in solid-state compounds shall help to interpret the experimental results. Calculations of main group and transition metal oxides and halides in the gas phase and the gas phase-solid state interactions are another point I am focusing on. That is of course an important factor in heterogeneous catalyses and in surface chemistry as well as in the simulation of chemical transport reactions.