Elke Schwöbel

Bruker AXS GmbH, Karlsruhe, Germany

CV:

Master degree in Geology at the Rupprecht-Karls-University Heidelberg

Main research interest: Clay Mineral Stratigraphy in Triassic sediments investigated with X-ray diffraction techniques

Application scientist for X-ray diffraction at Bruker AXS GmbH since 1997

Responsibilities:

- all applications relevant for industrial customers

- sample analysis, method development, and demonstration of XRD instruments

- XRD instrumentation and software instructor also giving numerous workshops with international attendance

Quantitative XRD-Analysis of Phases with known, partial or No Known Crystal Structures

In recent years the Rietveld method emerged as a routine tool for quantitative phase analysis of X-ray diffraction data. The basics of the method were published in the late 1960´s, when the Dutch crystallographer Hugo Rietveld presented computer based analytical procedures making use of a complete powder diffraction pattern. Fast and reliable results became possible by combining modern computer technology and the optimised mathematical algorithms with the fundamental parameters approach.

Quantitative phase analysis via the conventional Rietveld method is generally restricted to crystalline phases with well known crystal structure, where peak intensities are calculated from the crystal structural data. Nonetheless, unidentified, structurally uncharacterised, and amorphous materials may be quantified altogether by spiking the mixture with an internal standard. However, this can only give the total abundance of all compounds with unknown crystal structure - a quantification of individual phases is not possible.

In contrast, the method of quantitative analysis of phases with Partial Or No Known Crystal Structures, PONKCS [1], allows the accurate quantification of individual compounds. Using PONKCS, crystal structure information is replaced by measured intensities from a reference sample, simply requiring a one-time calibration using an internal standard. As a result, extremely accurate results can even be obtained in cases where the classic Rietveld method cannot be applied at all.

The methodology and practical examples will be presented.

[1] Scarlett, N.V.Y. & Madsen, I.C. (2006): Quantification of phases with partial or no known crystal structures. - Powder Diffraction, 21(4), 278-284