[
Introduction |
Research |
Optical transforms |
Group members |
Publications ]
Our research group combines diffuse X-ray scattering methods with computer
simulation and optical diffraction modelling to deduce the arrangements of
atoms and molecules in disordered crystals. Conventional crystal structure
determination reveals only averaged arrangements, inadequate to explain
some of the basic properties of the many minerals, inorganic compounds,
organic compounds and alloys which exhibit crystalline disorder.
Diffuse scattering gives information on how neighbouring atoms or molecules
interact with each other. Quantitative studies of diffuse scattering are,
however, still rare because of the intrinsically very low intensities involved.
The Disordered Materials Group had developed a dedicated diffuse-scattering
diffractometer system based on the Stoe curved position-sensitive wire detector
(PSD). This allows high quality diffuse scattering data to be efficiently
recorded over large volumes of diffraction space and provides a unique facility
for tackling a whole range of problems not previously feasible. A second
instrument has now been constructed, which, as well as providing additional
data collecting capability,allows measurements to be made with Mo-Kalpha
radiation and is suited to a range of materials that were too highly absorbing
for investigation on the original system which used CuKalpha radiation only.
The group's interests span a wide range of different fields, each presenting
problems for which this specialised technique can give unique information.
Disordered molecular crystals
including ones having e.g. anomalous optical properties. Here the aim is to
understand the basic interactions between molecules, how these give rise to
the particular state of order and the relationship of this to the physical
properties of the materials.
Non-stoichiometric inorganic materials typified, e.g. by the cubic
stabilised zirconias and mullite which is a major component of all
aluminosilicate ceramics. these both have commercially important properties
which are intimately associated with their atomic ordering patterns.
Wüstite is another material in the category which is important because it
is thought to be a major constituent of the earth's lower mantle. Any
description of the structure of these materials which does not account for the
complex diffuse diffraction patterns they exhibit, cannot hope to
satisfactorily explain their properties and behaviour.
Flexible open-framework structures such as SiO2 silica polymorphs
cristabolite and tridymite and their analogues. Also included in this category
are guest-hosts systems such as urea inclusion compounds and zeolites, which
are important catalytic materials.
Quasi-crystal phases which have been found in a large number of
alloy systems since the original discovery in 1984, have attracted the group's
attention recently, not only because they present fundamentally new concepts,
but also because it is clear that in many cases disorder is an important aspect
of the problem.
T.R. Welberry (Group Leader) -
welberry@rsc.anu.edu.au
Andrew Christy (Visiting fellow) -
christy@rsc.anu.edu.au
Darren Goossens (Post-doc) -
goossens@rsc.anu.edu.au
Matthias Honal (Visiting fellow) -
honal@rsc.anu.edu.au
Aidan Heerdegen (Graduate student) -
aidan@rsc.anu.edu.au
Diffuse X-ray scattering and models of disorder. Rep. Prog. Phys.,
48, 1543
(1985).
Optical transform and Monte-Carlo study of phason fluctuations in quasi-periodic
tilings, J. Appl. Cryst., 24, 203 (1991).
Oxygen vacancy ordering and the incommensurate structure of mullite. With
B.D.Butler and R.L.Withers, Phys. Chem. Minerals., 20, 323 (1993).
A 3D model for the diffuse scattering in cubic stabilized zirconias. With
B.D.Butler, J.G.Thompson and R.L.Withers, J. Solid State Chem.,
106, 461
(1993).
Interpretation of diffuse X-ray scattering via models of disorder. With
B.D.Butler, J. Appl. Cryst., 27, (1994).