STUDY OF THE TEMPERATURE-DEPENDENCE OF THE HYPERFINE PARAMETERS IN 2 ORTHOPYROXENES BY FE-57 MOSSBAUER-SPECTROSCOPY

Fe-57 Mossbauer measurements were performed on two natural orthopyroxe nes in the temperature range between 17 and 490 K. The temperature var iations of the center shifts and of the quadrupole splittings have bee n interpreted using the Debye model for the lattice vibrations and the crystal-field model respectively. Two approaches have been applied to evaluate the crystal field. The first one, which is commonly used by Mossbauer spectroscopists, emanates from the approximative and simplif ied symmetry of the ferrous sites, whereas the second one takes into a ccount the real C1 symmetry of the ferrous sites, thus leading to a po int-charge calculation. For comparison, analogous calculations have be en carried out on literature data for an iron-rich orthopyroxene (spec imen XYZ).