Applications

The synthesis of high performance alloys and ceramics is a growing area. Highlighted here are two examples to demonstrate the scientific aims in this subject area. First, the use of oxynitride materials instead of zirconia to simulate toughening in silicon nitride and sialon ceramics, which show a similar martensitic transformation to that in zirconia has been proposed. The transformation temperatures of these new solids are expected to be 1500-1800 K with small changes in unit cell volume (~ 0.5-1.0%). Moreover, the oxynitrides are of the cuspidine type, exhibiting considerable pseudosymmetry which gives rise to numerous doublets in the powder pattern. The high resolving power of I11 will be ideally suited to this kind of problem. In situ work to investigate the alpha-to-beta sialons transformation at 1500-1800 K will reveal new structural information including a residual liquid phase that may crystallize to form oxynitride phases, which in turn can undergo further transformations on cooling.

Secondly, the uses of titanium alloys in engineering applications are increasingly widespread. These materials have very good mechanical properties allied to excellent corrosion resistance. Although it is widely known that the properties of Ti-alloys depend essentially on the microstructure formed during thermo-mechanical processing, there has been little in situ work done on understanding the nature of the phase transformations taking place at differing stages of heat treatment. Each of these studies would benefit greatly from I11, which will have a low instrumental contribution to peak broadening and fast data acquisition rates coupled to the use of high temperature attachments.

The macroscopic properties of thin films and multilayers are strongly influenced by the preferred orientation of crystallites, strain and chemical variation or composition. The ability to perform non-destructive stress/strain, depth-profiling of composition and texture analysis on this beamline will be important to the manufacturers (academic and industrial) of these items. As part of a larger research programme, these measurements are central to understanding the relationship between structure and physical properties, for example the magnetism of thin transition metal films for magnetotransport devices (spin valves). Texture measurements on the material layers are also critical to determining whether Fermi surface or interface scattering dominates the magneto-transport. Studies of stress and strain in semiconductors and the probing of the depth distribution of structural defects are all achievable objectives using I11. All these data will contribute to the feedback loop necessary to improve or fine tune production techniques.
 

I11 is a powerful instrument for determining new structures and elucidating the subtle responses of known structures to changes in temperature, applied stress and chemical variations. It provides the mineralogical community with the means to investigate the behaviour of naturally occurring materials. Aside from the mature fields of mineral physics, and the insights it provides into the workings of planetary interiors as well as surface processes, I11 has benefits in the field of biomineralisation, for the analysis of the mineralisation of microbial mats which, for example, is now recognised as an important (but poorly understood) mineral process within environmental science.

The ability to collect high resolution data at rapid rates enables the study of fast kinetic and non-equilibrium phenomena (such as rapid cation exchange, associated charge ordering and even defect ordering) in terms of elastic contributions to the spontaneous strain across the lattice. This has been found to be important in a number of minerals, where the main energetic influences are mediated via strain and elastic energy terms.

Almost any change in the structure of a crystal, due to small atomic displacements, atomic ordering, magnetisation, etc., is usually accompanied by changes in lattice parameters. If suitable reference states are defined, such lattice parameter variations can be described quantitatively as a combination of linear and shear strains. Thus what was originally a geometrical description can become a thermodynamic description if the relationships of the strains to the order parameter are also defined. Spontaneous strains due to phase transitions in silicates and oxides can be as large as a few %, but even small variations of ~0.1 % will be detectable using this high resolution SXPD beamline. 

The fact that the efficacy of drugs can be critically affected by the environment (humidity, pressure and temperature) has driven a large amount of research effort into crystalline pharmaceuticals, their structures and transformations. For example, recent work on the structural transformations in Zopiclone (a drug for treatment of insomnia) has clearly demonstrated the effectiveness of SXPD. The results are academically interesting and commercially beneficial; better drugs can be manufactured in optimum (i.e. cheaper) conditions at production plants. The ability to vary temperature (T) and pressure (P) simultaneously and collect data rapidly would represent a quantum leap forward, enabling researchers to map out the P-T phase diagrams for solid-phase pharmaceuticals. The value of the I11 beamline to this area of research is increased through the provision of accurate humidity control to allow structural investigations of hydration/dehydration processes in drugs. This area of synchrotron x-ray work is very complementary to existing programmes which utilise neutron powder diffraction. 

Structurally interesting transition metal oxides in the form of solid solutions often have interesting physics. These include charge density wave materials (e.g. Ba1-xKxBiO3), in-commensurate high temperature superconductors (e.g. Bi2Sr2CaCu2O8), colossal magnetoresistance manganites (e.g. Sr0.5Nd0.5MnO3), and charge stripe nickelates (e.g. La2-xSrxNiO4). These materials share both a fascinating physics, involving strongly correlated charge, spin and orbital ordering, with far reaching potential applications in superconductivity, magnetic media and sensors. High quality SXPD data are required to refine the complex chemical structures in order to accurately interpret their strange magnetic, electrical and thermal behaviour. The ability to perform resonant x-ray diffraction on the I11 beamline will help in establishing accurate cation coordinates, particularly in those materials with neighbouring elemental metals. In addition, with the combination of energy tuneability and high flux, even magnetic diffraction peaks have been observed in antiferromagnetic powders using synchrotron beamlines.

Many of the most topical metal oxides and chalcogenides have crystal structures that approximate to a simple arrangement, such as the perovskite or spinel types, but with small lattice distortions that usually lead to lower symmetries and superstructures. This is evidenced by the presence of peak splitting and very weak diffraction features originating from super lattice structures. The distortions are not minor details, but are often the key to understanding the properties of these materials. Typical examples are Jahn-Teller distortions in manganese oxide battery and CMR (Colossal MagnetoResistance) materials, polar distortions in titanium oxide ferroelectrics and valence ordering distortions in the CMR materials and in spinels such as magnetite and CuIr2S4. However, these distortions invariably lead to twinning, making it impossible to synthesise high-quality single crystals, at least in the early and fast moving stages of research on new materials. Consequently, powder diffraction has historically been the tool of choice for the study of novel compounds in this class. High-resolution synchrotron diffraction is an ideal complement to neutron diffraction in many of these studies, since it is common for structural models to be determined against both types of data to solve complex problems. The high resolution of the I11 beamline will provide a significant increase in data quality, resulting in greatly improved fits for such models.

With outstanding dielectric properties, families of oxide perovskite microwave dielectric ceramics (e.g. Ba-Nd-Ti-O and Ba-Zn-Nb-O) are the new materials of choice for high frequency applications in the telecommunication industry. These complex perovskites will, for example, contain Nb plus a divalent ion on the B-site. Depending on the actual combination of ions on the B-site, the octahedra units suffer varying degrees of tilt, which has a significant impact on the ceramic’s dielectric properties. A second important issue is the development of ordering or disordering, depending on both composition and manufacturing details (e.g. sintering temperature). The exceptionally high flux and d-space resolution of I11 will allow materials scientists to fully characterise the nature of octahedral tilting and degree of ordering in these industrially important microwave materials as well as the temperature dependence of such phenomena in ceramics prepared by either mixed oxide, or chemical routes.

The features of this high-resolution beamline are essential for the characterisation of the new complex materials required for future communications technology (dielectrics and ferroelectrics, magneto-resistive materials) and energy needs (fuel cell and battery electrodes, photo-catalysts). Understanding fundamental structural properties by "following" synthesis processing using time resolved measurements, will lead to the production of new tailor-made materials with desirable applied characteristics. Layered double hydroxides that have application as new drug delivery systems, functionalised mesoporous materials for application in catalysis and porous three-dimensionally connected actinide-containing materials used as ion-exchange materials in radioactive waste treatment are a few examples that will benefit from this beamline. In situ synchrotron X-ray powder diffraction (SXPD) will also play a vital role in elucidating changes in the structures of zeolites and other microporous materials. 

This topical field presents the largest area of interest and activity within our powder diffraction community. Solid metal oxides and chalcogenides are an important group of inorganic compounds, with uses in magnetic, conducting, superconducting, battery, ferroelectric and catalytic applications. The materials are typically prepared and used as polycrystalline ceramics or powders, making powder diffraction a key characterisation method. Although good X-ray diffraction data can be obtained from modern laboratory instruments, significant improvements in resolution and signal-to-noise ratio will be achieved on I11. These improvements will be decisive in many aspects of structure determination and refinement. Another important aspect of a synchrotron x-ray source is its unique tuneability, enabling resonant (anomalous scattering) effects to be exploited. This yields element specific information that is particularly valuable in disordered and mixed anion materials (disorder is a common feature, because of deliberate chemical doping and/or the high temperatures used for sample preparation). This again can be used in tandem with neutron data, to provide scattering contrast for some elements. The advanced design and ease of wavelength scanning proposed for Beamline I11 will make it the instrument of choice for such studies

The collection of high quality powder patterns at fast rates (microsecond – millisecond per pattern) is not currently possible using conventional detector systems. However, with the combined development of the fast detector (PSD) and the inherent high flux, studies of extreme reactions by chemists and materials scientists to provide temporally-dependent structural details will be possible on this beamline on a routine basis. The powder data, collected with ms-ms resolution, will help researchers to further current understanding of the fundamental principles behind fast processes such as explosive compounds, solid state combustion and rapid oxidation. For example, self-propagating high-temperature synthesis (SHS) is a solid state combustion technique recently developed at University College London. The controlled reactions of ferrous oxide with other metal (Zn, Mg) oxides and NaClO4 powder can form a mixture of ferrites in seconds.

Interestingly, in situ energy-dispersive powder patterns have shown that the application of a magnetic field during the SHS reaction significantly modifies the mechanical (micro-structure), magnetic and crystallographic properties of the products. The diffraction results were extremely useful and allowed the identification of the material phases produced, along with the determination of their basic crystalline structures. However, the data quality particularly at intermediate stages where the science is most interesting (death and birth of structures), was limited by the speed of the diffraction experiment (incident x-ray flux and the detector performance) and low d-space resolution. Significantly better quality data are needed in order to give detailed quantitative information regarding structural changes including atom/molecular arrangements, bond lengths and angles. These results would directly contribute to the unravelling of the chemical-physical conditions responsible for the violent collapse and sudden formation of different phases. In conditions where there is little or no control (e.g. fireworks, explosives and thermite reaction), SHS combustions are in fact extreme chemical reactions in which temperatures of more than 2000 K are generated, allowing single-phases to be made almost instantly. In this regime, time scales are much shorter (ms-ms) compared to seconds for controlled experiments. For such fast reactions, data acquisition speeds must be capable of matching the process in order to reveal the underlying science. The capability of the new PSD detector and the beamline’s high flux represent the optimum design that will allow users to investigate ultra-fast materials processing and extreme chemical reactions, which at present are not possible with existing SR facilities.