Pair distribution function analysis of ammonium nitrate-comparison of PDF- and Rietveld-analysis

Energetic materials are often nanocrystalline, amorphous, liquid or gel structured. Therefore, it is difficult to obtain structural information from these materials by conventional structure analysis using X-ray diffraction. The contribution shows the possibility to achieve structural information from laboratory measurements with the aid of the pair distribution function (PDF) compared to the Rietveld-Analysis. The energetic material ammonium nitrate was chosen as an example for the test of PDF structure analysis of energetic materials. The diffraction data were used for calculating the PDFs and the results are evaluated in order to improve measurement conditions for energetic materials.
The comparison of the lattice constants, calculate by Rietveld- and PDF-Analysis yielded reasonable values, when compared to literature data. Overall, the investigations yielded reasonable PDFs of ammonium nitrate using X-ray laboratory equipment. Hereby, the X-ray measurement, from which the experimental PDF is then generated with the aid of Fourier synthesis, is of crucial importance. In order to generate a meaningful PDF, high demands must be placed on the X-ray measurement. For example, a variation in tube voltage can have a negative impact on the quality of the experimental PDF. Considering all the necessary factors that can influence the PDF, it is quite possible to obtain comparable results from PDF analysis and Rietveld refinement. Moreover, PDF analysis is a good tool to obtain structural information from low crystallinity explosives, where Rietveld-analysis is hardly possible.