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’’O_8.5 (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 LnFeAsO_1-xF_x 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 NdMnAsO_1-xF_x, 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.