High Pressure III. DAC Image Plate Combination

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DAC Image Plate Combination

The advantages of the DAC - image plate combination are that:

• The poor sampling statistics inherent in DACs: Because the sample volume is so small there are relatively few crystallites present compared to normal powder diffraction and the powder diffraction rings are therefore "spotty". However the image plates records all or parts of these rings and by summing up the information around the rings the spottiness can effectively be removed. This process is referred to as "integrating around the Debye-Scherrer ring" and the result is illustrated below:

  Image Plate Debye-Scherrer rings:

  Integrated pattern:

• The ADD mode produces much sharper diffraction peaks than the EDD mode and this therefore yields more information and better structure refinements; the difference is illustrated below, for an InSb sample studied by both methods:

• The use of DAC-ADD systems has been very fruitful over the last decade permitting phase diagrams and equations of state to be measured for a wide range of materials from semi-conductors to ices. A typical result, by M. McMahon is shown in the following image plate illustrating the sharp phase transition observed in InSb while increasing the pressure from ambient to 49 kbar:
  

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