Order, Disorder, Flexibility, Function

Andrew Goodwin

Inorganic Chemistry Laboratory, University of Oxford

The existence of internal degrees of freedom in a material is often directly responsible for unusual physical behaviour or some particular functional response. In the case of mechanical degrees of freedom, for example, this behaviour might include negative thermal expansion, negative compressibility, and other elastic anomalies. In the case of magnetic degrees of freedom, the interest is often in the emergent behaviour of collective spin entities (e.g. in spin liquid states). Structural disorder nearly always plays a key role, and the most interesting examples are those in which that disorder is strongly correlated rather than random.

This talk will explore the role of geometry in some relevant systems where disorder and/or flexibility are crucial for material function, drawing on studies of molecular frameworks, nanoparticles, ‘hidden order’ magnets and low-dimensional materials. The general problem of structurally characterising disordered states of matter will form a central part of the talk.

Relevant references:

“The crystallography of correlated disorder”, Nature 521, 303 (2015)

“Giant negative linear compressibility in zinc dicyanoaurate”, Nature Materials 12, 212 (2013)

“Hidden order in spin-liquid Gd3Ga5O12”, Science 350, 179 (2015)

“Encoding complexity within supramolecular analogues of frustrated magnets”, Nature Chemistry (in press)

“Design of crystal-like aperiodic solids with selective disorder-phonon coupling”, Nature Communications (in press; preprint at arxiv:1508.05909)