synthesis, structure and properties of solid-state materials
My research approaches functional solid-state materials by focussing on structure as the key that relates their chemistry to their properties. These projects all involve synthesis, physical property measurements, crystallography and spectroscopy (especially neutron and synchrotron x-ray scattering). They also make use of ab initio (DFT) calculations and simulations to help understand structure and dynamics in the target materials, and to interpret experimental results.
Stabilising the fastest of fast-ion conductors with high valent transition metals
The high-temperature form of bismuth oxide, δ-Bi2O3, is the best ionic conductors known. It is only stable above 750°C, but this can be fixed by “doping” with transition metals such as Nb, Mo or Re to create stable materials potentially suitable for use as solid-oxide fuel cell membranes. However, the dopants also give rise to complex local ordering of oxide ions in their vicinity, which are scientifically fascinating but which degrade performance. This project seeks to understand how that ordering affects stability and conductivity, and use that understanding to develop new materials. In particular, we will explore whether certain dopants (e.g. Mo6+) can be arranged to participate cooperatively in ionic transport, enhancing rather than degrading the conductivity. The project will involve high-temperature synthesis, neutron scattering and ab initio dynamics simulations.
Novel hydrated oxides for mixed ionic-electronic conduction
Mixed ionic-electronic conduction (MIEC) is a rare property required for fuel-cell electrodes, as well as oxygen and humidity sensors. We recently discovered and characterised a new class of hydrated oxides Ba4M2O9.xH2O (M = Nb, Ta, Sb) that exhibit MIEC due to the presence of large voids and discrete hydroxide ions across three different structural forms. The key breakthrough was to grow cm-sized single crystals in our floating-zone furnace (FZF) – a first for these materials. This project will design a series of new barium oxides that should show MIEC behaviour, and use the FZF technique to synthesise them as large single crystals. We will use the crystals for physical property measurements, synchrotron x-ray spectroscopy and neutron diffraction. It will be particularly interesting to carry out depth-dependent measurements on the smooth, polished crystal faces, in order to better understand the “core/shell” nature of the hydration process and how that affects kinetics, and hence performance.
Naturally layered multiferroics: combining properties on an atomic scale
Multiferroics exhibit both ferroelectricity (electrical polarisation, used in capacitors) and ferromagnetism (spin polarisation, used in transformers and data storage devices). They have important applications as sensors, actuators and – potentially – a new generation of data storage media. Unfortunately, because the two properties are usually mutually exclusive in a single material, all the multiferroics in current use are simply multilayer sandwiches of bulk ferroelectric and ferromagnetic materials. In this project we will attempt to resolve this incompatibility via a new approach, in which we take naturally layered ferroelectric oxides and use them as “templates” into which we can substitute single atomic layers of magnetic cations. The project will involve: sophisticated synthetic techniques including sealed-tube controlled atmosphere reactions at high temperatures and “templating” intercalation reactions at moderate temperatures; neutron and x-ray diffraction; and magnetic/electronic properties measurements at low temperatures (down to 1.5 K).
For further information, please contact:
School of Chemistry
University of Sydney NSW 2006
Phone: +61 2 9351 4780