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Abstract
Crystalline solids are defined by the concept of a periodic, repeating, ordered, spatial array of chemical species.  Whilst this idealised picture is helpful there are a number of curious, and technologically important, examples of crystalline solids that exhibit high degrees of disorder.  I am interested in understanding this disorder in terms of crystallography and thermodynamics, and the role it plays in stabilising highly unusual physical properties.
Thermodynamics requires materials to form more ordered structures at lower temperatures and this entropic requirement drives their evolution towards a ground state as they are cooled. In specific magnetic materials it is possible to inhibit this, and so drive these materials towards highly degenerate states, dynamic behaviour, or quantum magnetic states as we approach liquid helium temperatures.  We examine examples of these frustrated perovskites using a combination of compositional control, neutron diffraction and magnetic measurements.
I will also present examples of extreme disorder in lithium-containing garnets.  These highly crystalline phases have the chemical and mechanical properties typical of ceramics but contain Li+ ions that are highly mobile at room temperature.  The ionic conduction in these ceramic materials approaches that of liquid electrolytes and these materials are at the heart of the next generation performance of all solid-state batteries.