Research Overview
Solid state materials are of fundamental importance due to the plethora of exciting physical properties that have been detected and applied in technological applications. We are interested in synthesising novel materials that exhibit fascinating electrical (ionic conducting) or magnetic properties.
Rietveld refinement of crystallographic models from X-ray and Neutron powder diffraction data (at facilities such as ISIS, Rutherford Appleton Laboratory, Didcot, UK and the ESRF and ILL, Grenoble, France) are used in order to correlate the structure-property relationships in the novel synthesised compounds which enable us to tune the properties of our materials.
Research Expertise
Solid state synthesis
Rietveld refinement of crystallographic models from X-ray and neutron powder diffraction data
Characterisation of ionic condctors via impedance spectroscopy
Electronic and magnetic characterisation of novel oxides and pnictides
Magnetic structure determination
Research Facilities
A suite of high temperature tube and box furnaces (up to 1600 oC) for solid state synthesis
Two top of the range diffractometers (Panalytical X’Pert Powder and Empyrean powder diffractometers)
Variable temperature impedance jig coupled to a Solartron SI 1260 Impedance/Gain-Phase Analyser
Stanton Redcroft TG/DTA
Departmental access to a Mettler Toledo TGA 2 coupled with a Hiden Quadrupole Mass Spectrometer
Departmental access to a Carl Zeiss Gemini SEM 300 to determine the microstructures of samples in addition to EDX measurements
Current Research
Oxide Ion Conductors
Solid oxide fuel cells (SOFCs) are electrochemical devices able to generate electricity from renewable energy sources, with high efficiency and low emissions of pollutants. However, oxide ion transport in most commercially available solid electrolytes is enabled only at high working temperatures (> 700 °C), thus making the commercialization of SOFCs particularly challenging. The high operating temperature reduces the components’ durability, results in slow start up times and the necessitation of expensive materials for seals and interconnects. In order to overcome these issues, it is desirable to develop novel electrolyte materials with significant oxide ion conductivity at intermediate temperatures (300 – 600 °C). Ionic conduction in solid oxides is strongly related to the crystal structure, and as a result the discovery and characterization of novel oxide ion conductors in various structural families has attained significant attention from researchers. We have been investigating hexagonal perovskites Ba3M’M’’O8.5 (M’M’’ = VW, NbMo, NbW) which exhibit highly disordered crystal structures and state-of-the art conductivity. We are currently interested in synthesising new materials with different combinations of M’M’’ to see how the chemistry controls the ionic conductivity.

Mixed Proton/Oxide Ion Conductors
We are also interested in mixed ion conductors, specifically mixed oxide-ion and proton-conductors. Such dual ion conductors have been proposed as a new class of electrolyte for intermediate temperature ceramic fuel cells, as they exhibit low ohmic resistance without external gas humidification. We have been investigating the electrical and structural properties of Ba7Nb4MoO20, a cation-deficient 7H hexagonal perovskite derivative formed by an intergrowth of palmierite layers and 12R perovskite blocks. Ba7Nb4MoO20 supports remarkable oxide ion and proton conductivity with excellent chemical and electrical stability over a range of pO2. The ionic conduction properties of Ba7Nb4MoO20 are linked to its distinct disordered crystal structure. Ba7Nb4MoO20 supports pure ionic conduction with high proton and oxide ion conductivity at 510 °C (the bulk conductivity is 4.0 mS cm-1) and hence is an exceptional candidate for application as a dual-ion solid electrolyte in a ceramic fuel cell which will combine the advantages of both oxide ion and proton conducting electrolytes. We are currently performing chemical doping studies to further enhance the conductivity.

Magnetic Materials
The recent report of high temperature superconductivity in oxypnictides such as LnFeAsO1-xFx with superconducting transition temperatures (Tcs) up to 55 K has led to a rapid expansion in the research of oxypnictide materials. We have recently discovered the counterpart, colossal magnetoresistance (CMR) in Mn2+ based oxypnictides NdMnAsO1-xFx, so that both manifestations of correlated electronic behaviour are now found in these new materials. Colossal magnetoresistant materials exhibit a large change (> 90%) in their electronic resistivity upon application of a magnetic field and have application as magnetoresistive sensors and spintronic devices in which electron spins are used to process information. We are currently investigating more complex cation ordered oxypnictides such as Sr2Mn2CrAs2O2 which exhibit spin reorientation magnetic transitions upon cooling which may show coupling between magnetic and electronic degrees of freedom.

Research Funding and Grants
We have had funding from a range of sources including EPSRC, the Leverhulme Trust, Institut Laue Langevin, the Commonwealth Scholarship Commission, Chief Scientist Office and the Royal Society.
If you’re interested in joining the group as a PhD student, please email a.c.mclaughlin@abdn.ac.uk.