Low-Temperature Anharmonicity in FeCl2

Abstract

Mossbauer spectra of Fe 57 in thin anhydrous ferrous chloride powdered absorbers have been investigated at several temperatures between 300 and 10°K. The quadrupole splitting, velocity shift, and Mossbauer fraction have been determined. The Mossbauer fraction of FeCl2 shows an anomalously weak temperature dependence which cannot be explained by any harmonic model for the interatomic forces or by the usual hightemperature anharmonicity. This anomalous behavior implies a low-temperature anharmonicity which is qualitatively explained in terms of the relative sizes of the ions involved. The interpretation is consistent with the finding of essentially harmonic behavior for FeF2. The results of our reexamination of other Mossbauer / studies are also consistent with these size arguments.

Activity Transfer of Radioiron and Mössbauer Spectra in the Sodium Pentacyanonitrosilferrate and Ferric Hydroxide System

“…The loose binding is produced by the interaction of the ion with the ligands of the neiboorhing pentacyanonitrosilferrate molecule. Since the distance between the ferric hydroxide and sodium pentacyanonitrosilferrate molecules is relatively large, the size of the surrounding cage is not limited by the overlapping iron-oxydril electron groups but by oxydril-oxydril electron groups overlapping, as it has been stated in ferrous chloride system [12].…”

“…The decrease of the temperature reduces the frequency of the atom transition and in this why the iron ion can remain in the Potential energy well a time interval comparable to the gamma transition period in the radioactive source decay. It is why the Mössbauer effect allows determinations of certain integral moments of the frequency distribution, which are sensitive tests of harmonicity [12], This behaviour of Fe(OH) j in the annealed mixture can be explained considering that Fe (III) ion is relative loosly bound by the OH groups as compared to the non annealed sample. The loose binding is produced by the interaction of the ion with the ligands of the neiboorhing pentacyanonitrosilferrate molecule.…”

Étude théorique du couplage magnéto-élastique dans FeCl2 I. — Applications : propriétés a très basse température, kT << 12 cm-1

“…Elle doit exister même à basse température puisque D. P. Johnson et J. G. Dash [25] concluent à partir d'expériences d'effet Môssbauer sur FeCl2 que les termes anharmoniques du potentiel internucléaire ne sont pas négligeables même à basse température.…”