ABSORPTION - CAN WE FIGHT IT?

Derk Reefman

Philips Research, WY 41, prof. Holstlaan 4, 5656 AA Eindhoven, The Netherlands, reefman@natlab.research.philips.com

Compared to the early days, quantitative analysis by X-ray diffraction has reached a level where it is really quantitative, instead of only qualitative. This tremendous progress has been achieved by several improvements on different aspects of powder diffraction: the equipment itself has become more stable, accurate standards have become widely available, and impressive improvement has been realised in methodology, such as a full Rietveld refinement on a multi-phase sample.

In principle, Rietveld refinement offers full control over all factors influencing the diffracted intensity. Failure of the Rietveld method, therefore, merely indicates a shortcoming in the description of the diffraction process.

Amongst these shortcomings, are the effects of absorption contrast and sample transparency. Though the first can often be minimised by careful sample preparation, and the second only occurs for highly transparent samples, clearly situations occur where one of these effects seriously hinders accurate quantitative analysis.

In the presentation, some of these practical problems will be outlined, and some newly developed approaches to these problems will be addressed. Typical results will be discussed, as well as the general applicability of these methods.