Dielectrics and Conductors

The functionality of dielectrics and conductors most frequently lies in some form of molecular or ionic disorder. Accordingly, if we are to become able to tailor materials to suit a specific dielectric or (super)conducting application, we need to understand this disorder at the atomic and molecular level.

The most revealing of materials characterization approaches to quantify ionic or molecular disorder is X-ray or neutron diffraction. Specifically, a wealth of structural information can be drawn from the diffuse scattering features that surround Bragg positions in a crystal structure, in cases where disorder is prevalent. By capturing this information, we can start considering molecular design principles that will enable the molecular engineering of more advanced dielectric and conducting materials.

By way of a few examples, we have previously sought to unravel the nature of the disorder in chlorobenzene derivatives, which is responsible for their anomalous dielectric properties. We are currently investigating diffuse scattering signatures in a new class of superconductors (iron arsenides).

Selected publications

• J. M. Cole, H-B Bürgi, G. J. McIntyre

  Distinction of disorder, classical and quantum vibrational contributions to atomic mean-square amplitudes in dielectric pentachloronitrobenzene

  Physical Review B 2011 83 224202 (1-11)

• P. L. Alireza, Y. T. C. Ko, J. Gillett, C. M. Petrone, J. M. Cole, G. G. Lonzarich, S. E. Sebastian

  Superconductivity up to 29 K in SrFe₂As₂ and BaFe₂As₂ at high pressures

  Journal of Physics: Condensed Matter 2009 21 012208

• L. H. Thomas, J. M. Cole, C. C. Wilson

  Orientational disorder in 4-chloronitrobenzene

  Acta Crystallographica C 2008 64 0296-0302

• L. H. Thomas, R. T. Welberry, D. J. Goossens, A. P. Heerdegen, M. J. Gutmann, S. J. Teat, P. L. Lee, C. C. Wilson, J. M. Cole

  Disorder in pentachloronitrobenzene, C₆Cl₅NO₂: a diffuse scattering study

  Acta Crystallographica B: Structural Science 2007 63 663-673