X-ray diffraction is a technique that may be used to probe the structure of crystalline materials at a number of different levels of detail. X-ray diffraction patterns consist of a number of intense peak or ‘reflections’ at specific angles and contained within this pattern is information that may be as detailed as where all the atoms are within the structure. However these peak positions may be used more simply as a fingerprint, to identify the crystalline phase or phases in a sample, either qualitatively or quantitatively. The technique is non-destructive and can be applied to a wide variety of materials, such as ceramics, metals, polymers and composites in a variety of forms such as powders, solids and thin films.
The Brüker D8 Advance diffractometer is a vertical footprint goniometer configured in θ-θ geometry (i.e. the sample is horizontal and the X-ray source and
detector move). It is configured with a CuKα X-ray source with a number of other fixtures available for different measurements
- The standard geometry θ-θ geometry utilises a high resolution scintillation counter for excellent quality datasets suitable for structure refinement.
- Long Soller slits and LiF monochromator crystal setup available for thin film measurements also known as glancing angle or grazing angle measurements). Films down to 40nm have been characterised with this attachment
- A Lynx Eye silicon strip detector is also available as an alternative to the scintillation counter. This has similar resolution, but because of the 197 strips available, can reduce the count times by a factor of almost 200. with little loss of resolution. (See Figure below right).
- A 9 position sample changer allows continuous unattended data collection, enabling large numbers of high quality data sets to be collected routinely.
- An Anton Paar HTK16 high temperature stage capable of reaching 1600 C is available and easily exchanged with any of the other optics (centre and right hand imagers above). The chamber also has gas purge facilities, for either inert or reactive atmospheres. Coupled with the Lynx Eye enables real-time measurement of phase changes and melting phenomena
The Main Unique Aspects Of The Machine
- The modular design allows simple and rapid changeover to different configurations. On most changeovers, realignment is not required.
- The Lynx Eye detector allows high quality datasets to be collected in a fraction of the time for conventional scintillation detectors. This brings data refinement strategies into the realm of routine analytical methods and allows systematic studies to be performed in great detail
- The 9 sample auto-changer allows 24 hour unattended operation
- A significant suite of software is available for data analysis, this extends from The Brüker Eva package coupled with ICDD PDF-2 database for phase identification, through to the General Structure Analysis Software (GSAS) and also Topas for full structure determination. We also have a suite of Crystallographica Search/Match software available from Oxford Cryosystems
Examples Of Work Undertaken At The Institute
A wide variety of projects have utilised this technique for qualitative and quantitative measurement of a wide variety of parameters. For example (left hand figure below) we have measured and quantified the presence of a strained cubic phase in zirconia following grinding (lower trace) and the disappearance of this phase following a polishing procedure.
We have also carried out studies of the crystallisation of brushite in a calcium phosphate cement. The right hand figure below shows the appearance of the main reflection for brushite as the cement reacts. There are 120 datasets and each 3.5 range took 2 seconds to collect with an 8 second delay between each dataset capture.