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Vol. 25 No. 5
September-October 2003

Making an imPACt | Recent IUPAC technical reports and recommendations that affect the many fields of pure and applied chemistry.
See also www.iupac.org/publications/pac
 

Critical Review of Analytical Applications of Mössbauer Spectroscopy Illustrated by Mineralogical and Geological Examples (IUPAC Technical Report)

E. Kuzmann, S. Nagy, and A. V értes

Pure and Applied Chemistry
Vol. 75, No. 6, pp. 801-858 (2003)

A new terminology for Mössbauer pattern analysis has been developed in order to enhance the performance of qualitative analysis by Mössbauer spectroscopy. Mössbauer parameters are considered as a function of a number of externally adjusted experimental parameters at which the spectrum has been recorded. The basis of analytical classification is the microenvironment, which is determined by an assembly of atoms causing the same hyperfine interactions of one particular class of Mössbauer probe atoms. Since Mössbauer spectroscopy measures hyperfine interactions very sensitively, the microenvironment presents itself as a fundamental concept for analytical purposes.

The basic task of any qualitative analysis based on Mössbauer spectroscopy is to identify the individual physical or chemical species from the corresponding patterns present in the spectrum. Ideally, this can be done if we know the exact correspondence between patterns and species. Such a one-to-one correspondence between species of atoms and individual patterns, however, can be nonexistent for the given set of externally adjusted physical parameters at which the Mössbauer spectrum is recorded. For this reason it is useful to consider all the Mössbauer parameters (P) as a function of a number of externally adjustable physical quantities such as temperature (T), pressure (p), external magnetic field (H), polar angles (Q, f), frequency of high-frequency field (v), etc.

P = P (T,p,H, Q, f, v , . . .)

However, when the whole range of these parameters is considered, we may find points in the space of parameters at which only one pattern is associated with one species and vice versa and thus we can get around the problem of ambiguity.

From the analytical point of view we can introduce useful terminology classifying Mössbauer patterns. A spontaneous pattern is a Mössbauer spectrum measured at a given set of externally adjusted parameters (usually under standard conditions). The spontaneous pattern can be either a simple spectrum called an elementary pattern, reflecting only a hyperfine interaction at one particular microenvironment or a complex spectrum called superimposed pattern, which consists of a number of subspectra. Here we refer to a family of Mössbauer nuclei experiencing the same hyperfine interaction as a microenvironment. An induced pattern is a Mössbauer spectrum obtained under conditions other than the (mostly standard) ones selected for measuring the spontaneous pattern. In this case, the differences between the induced and spontaneous pattern can provide an important contribution to the analysis. The transformed pattern is obtained from the measured Mössbauer spectrum by mathematical transformation (e.g., by Fourier transformation). The magnetic hyperfine field distribution and the quadruple splitting distribution are transformed patterns. The transformed pattern can give a better resolution for the analysis.

Our approach can also contribute to the systematization of Mössbauer data for the identification of individual physical or chemical species from the corresponding patterns present in the spectrum. This new concept can also be generally applied on the field of analytical methods other than Mössbauer spectroscopy, and examples in the field of mineralogy and geology are included.

www.iupac.org/publications/pac/
2003/7506/7506x0801.html


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