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Messbauer spectra of the join Ge-Hd - Ge-Aeg and their N-spectra. The distinct intermediate structure.


At replacement of Ca ions by Na in position 2 in the first part of the pyroxene solid solution Nax Ca1- x FeGe2 O6 (at x(Na) < 0.5) the "host" ions Ca dominate in M2 sites and stabilize the Hd structure - the ions Fe2+ in 1 site keeps their electronic structure, characteristic for the Ge-analog of hedenbergite. At the gradual substitution of Ca by Na ions, in addition to the main doublet M1, in spectra appears one more doublet 1, having greater quadrupole splitting. As in M2 position of this solid solution the ions Fe 2+ should occupy (nominally) only the M1 positions, this additional M1a doublet has to be referred to Fe2+ in distinct sites of the M1 chain, which have in their nearest M2 site the ion Na1+ or cation vacancy. The doublet of ions Fe 3+, which appear in the solid solution, could be referred to the M1 sites also. The dramatic changes in spectra appears first at x(Na) = 0.7 and could mean the change of the structure. In any case, the distribution of local fields is not characteristic neither for Ca-rich, nor for Na-reach parts of the solid solution - in the spectrum dominates the M1 doublet with distinct, "specific" parameters. Small reflections of some additional (to the main monoclinic pyroxene) phase were found in the X-ray diffraction pattern of the sample and the correct estimates of composition of the main pyroxene phase could not be given.

In the Na- rich solid solution at x(Na) = 0.8 we get for ions Fe2+ in 1 sites (which are the "guest" ions in the aegirine structure) the other specific distribution of local field, characteristic for natural aegirine, studied in [Grave-98].

The distinct electronic states of Fe 2+ ions in pyroxene Ge-Si solid solutions were detected and characterized first in [Nov-99b, Nov0320E, Nov7EIZV] by the 57Fe gamma-resonance spectroscopy.

To improve the resolution of spectra (at the cost of signal-to nose ratio) and to resolve the overlapped components, the original N-procedure [N-Procedure] was used. The N-spectra were more effective at their more detailed visual comparative analysis, as well as at their numerical evaluation.