GENERAL ILL SEMINAR College VI

Monday, 20th September 2010 2:00 pm

Seminar Room – ILL 4 – 1st floor

David A. Keen ISIS Facility, Rutherford Appleton Laboratory, HSIC Didcot, Oxon, U.K

 Solid-state amorphization transitions, induced via heating or the application of pressure, significantly increase the range of materials that might yield amorphous phases. The debate about the materials that result from such transitions is whether they are ‘typical’ (i.e. similar to those produced via melt-quenching), whether they form a new amorphous class or indeed whether they should be classed as amorphous at all. Determination of their structure is the key to resolving this debate. Here we use atomistic modelling of x-ray and neutron diffraction to investigate the structures that result from pressure-induced amorphization (PIA) and temperature-induced amorphization (TIA) of ZrW2O8 and the zeolitic imidazolate framework material ZIF-4, respectively. In both cases the amorphous phase forms from a low-density crystal phase with a connected framework structure. We show that whereas amorphous ZrW2O8 has a structure that can be reconciled with a displacive-like phase transition from the crystal structure [1], the structure of amorphous ZIF is more akin to a continuous random network that would only come from ZIF-4 via a reconstructive phase transition [2]. As well as describing the phase transitions and structures of these two materials, we will discuss the implications of this work on PIA and TIA in general.

[1] D. A. Keen, A. L. Goodwin, M. G. Tucker, M. T. Dove, J. S. O. Evans, W. A. Crichton and M. Brunelli, Phys. Rev. Lett. 98 (2007) 225501

[2] T. D. Bennett, A. L. Goodwin, M. T. Dove, D. A. Keen, M. G. Tucker, E. R. Barney, A. K. Soper, E. G. Bithell, J.-C. Tan and A. K. Cheetham Phys. Rev. Lett. 104 (2010) 115503