Ling Group Research

Current PhD/Honours projects

The Ling Research Group

Stabilising fast-ion conductors with high-valent transition metals

The high-temperature form of bismuth oxide, δ-Bi2O3, is among the best ionic conductors known, but is only stable above 750°C. It can be stabilised to room temperature by “doping” with transition metals such as Nb or Re, creating potential solid-oxide fuel cell membrane materials. However, the dopants also give rise to complex local ordering of oxide ions in their vicinity, degrading 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.

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-scale single crystals in our floating-zone furnace (FZF) – a first for these materials – and use them for physical property and neutron scattering experiments. This project will use the FZF technique as the starting point to investigate the wide range of related barium oxides suspected of showing MIEC behaviour, but which have never been satisfactorily characterised.

Naturally layered multiferroics: bringing contradictory properties together 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. We will instead use naturally layered ferroelectric oxides as “templates” into which we can substitute single atomic layers of magnetic cations. Good progress was made in a previous project, but we reached an apparent limit of 50% magnetic substitution into a layer.

This project will explore a promising new strategy for reaching the desired 100%, by co-substituting halides (Cl–, F–) for O2– so that we can use lower-valent magnetic cations (e.g. Mn3+ instead of Mn4+), the size of which are a better match for the non-magnetic cations (e.g. Nb5+ or Ti4+) in the templates.

Cultivating complex magnetism in “platinum group” oxides 

Oxides of the platinum group metals (Ru, Rh, Re, Os, Ir) are a rich vein of fascinating magneto-electronic behaviour. Although their d-orbitals are less well defined than those of the first row transition metals, resulting in weaker superexchange, they show much greater structural flexibility and stronger metal-metal exchange. Despite this, they remain relatively underexplored due to the high cost and synthetic challenge of working with them.

We recently discovered a number of new platinum group oxides based on M2O9face-sharing octahedral dimers, which combine complex superexchange pathways with direct M–M exchange. They show unique low-temperature spin, charge and orbital phenomena.

Now that we have overcome the initial synthetic barriers, this class of compounds is ready to be explored in a full project.