The range of studies that may be carried out at the powder diffraction beamline includes:
- Ab initio structure solution
- In situ examination of chemical and mineralogical processes
- Structure/property studies
- Parametric studies, including variable temperature
- Phase identification and quantification
- Pair distribution function analysis
- Line profile analysis
- Examination of stress and strain
Synchrotron Powder Diffraction Advantages
Laboratory-based powder diffraction techniques are inherently resolution-limited in the range of observations (d-space range), the signal-to-noise ratio, and the shape and width of observed reflections. Synchrotron-based instruments are the only way to overcome these limitations and give the resolution required to determine and refine accurate structures of even moderately complex materials from powder samples. In addition, synchrotron measurements can be made on a 'real' time scale allowing observation of chemical processes.
Some of the advantages of synchrotron-based powder diffraction are:
- Improved signal to noise ratio
- Time resolved
High angular and energy resolution
- Large, accessible dynamic d-space range
- Narrower peak width and simpler shape
Tunable, monochromatic x-rays
- Flexibility in experimental set-up
- Ability to avoid or exploit absorption edges
- Hard x-rays penetrate bulky sample cells.
The powder diffraction beamline is expected to be used for studies in the following key areas.
Oxide based materials
The majority of advanced materials used in magnetic, conductivity, superconductivity, ferroelectric, catalytic and battery applications are solid metal oxides. This is a very high priority research area in Australia. Metal oxide chemistry is dominated by classes of materials having crystal structures derived from simpler parent structures such as perovskite or rutile. Small lattice distortions, which are critical to the key electronic and physical properties of these oxides, usually lead to lower symmetries and superstructures. These distortions are characterised by subtle peak splittings and the appearance of weak superlattice reflections in diffraction data. Typical examples include polar distortions in bismith oxide ferroelectrics, Jahn-Teller distortions in manganese oxide battery materials and valence ordering in colossal magneto-resistance materials (CMR). The detection and understanding of such distortions requires the high resolution afforded by synchrotron radiation.
An underlying feature of many of the most interesting materials is the strongly correlated behaviour of the electrons and coupling of the electronic charge and spin degrees of freedom with those of the electron orbitals and the lattice. The greatest potential for functionality is in materials at the edge of a structure and/or electronic instability where small changes in chemical or physical conditions lead to a major change in properties. Success here requires rapid data collection, which is only possible on a high brightness synchrotron radiation source.
Microporous and framework materials
Detailed knowledge of the crystal structure of microporous materials such as zeolites is required in order to understand their properties and improve their use of catalysts, sorbants and micro-reactors. These materials typically have large unit cells and it is common to observe complex patterns because of low symmetry or subtle distortions. In many cases a very high x-ray flux as delivered by a synchrotron source is the only way these problems can be studied.
Another application is in the study of a novel class of cyanide-bridge coordination framework solids that display negative thermal expansion behaviour. These have diverse potential applications in high precision and low thermal shock materials where the positive thermal expansion exhibited by the vast majority of materials is a hindrance. The ability to access low d-spacing - possible with synchrotron radiation - is critical in the study of the amplitude of such processes.
Mineral processing and soil sciences
Powder diffraction has been applied widely for analysis in the mineral processing industries. Laboratory techniques have traditionally been used; however, as ore grades become lower with increasing complexity in the mineralogy, improved peak resolution and peak-to-background ratios are required to conduct full characterisation. The synchrotron-based powder diffraction technique provides the inherent high resolution, high sensitivity and high speed capability that is critical in such studies.
This high speed capability will be used in studies where the sample environment emulates the processing conditions found in industry. The availability of a range of sample environments, including high temperatures and pressures, will be a key feature of this instrument.
Strain, texture and phase mapping
Powder diffraction has important applications in mechanical engineering, particularly in the mapping of residual strain fields, the detection of phases that degrade the material properties, mapping texture of the material, and determining grain size and the degree of cold work. High-energy synchrotron radiation (60 keV) enables measurement in the depth range of 0.01-1 mm. This depth range is very important as it is where most of the degradation of mechanical components originates. It also covers the thickness range of many protective coatings (e.g. thermal barrier coatings) and surface engineering treatments (e.g. laser shot peening).
The large flux of high energy x-rays available from insertion devices enables the two-dimensional mapping of strain, texture and phase in practical times. At each point of a map, a large area two-dimensional position-sensitive detector collects the rings of the diffraction pattern. Increasing the sample to detector distance provides information on cold work and grain size. Such maps are important in most areas of mechanical engineering (e.g. aerospace and power generation) and enable the integrity of newly developed procedures (e.g. welds) or aged components (e.g. turbine blades) to be assessed.
Furthermore, techniques are now being developed, with spiral or conical post sample collimators, to produce full three-dimensional maps of strain. Coupling the two- or three-dimensional mapping data with imaging data from beamline 10 (imaging and medical therapy) will increase the power of both the mapping and imaging techniques. Thus flaws can be located using beamline 10 and the associated strain fields mapped using beamline 3. Similar synergies may also be possible with other beamlines.
Powder diffraction has a key role to play in structural studies of pharmaceuticals and their interaction with low molecular weight peptides. Already powder diffraction patterns play a key role in unequivocally establishing the crystalline form of a pharmaceutical in a manufactured drug. Where the data has sufficient resolution, these methods will aid in understanding the solubility and dissolution of these forms.