Vol.
25 No. 5
September-October 2003
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.
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