MÖSSBAUER INVESTIGATION OF AMORPHOUS AND POLYCRYSTALLINE TELLURIUM

Résumé
La comparaison des spectres Mössbauer de ¹²⁵Te dans des films de Te amorphes et cristallins montre que dans la phase amorphe l'interaction quadrupolaire est légèrement plus élevée et que la fraction de résonance est réduite à environ un tiers de sa valeur dans la phase cristalline. Ces changements sont interprétés comme indiquant une diminution de la longueur de liaison covalente entre ions tellure proches voisins dans l'état amorphe et de plus que des liaisons oscillantes aux extrémités des chaînes de tellure provoquent un changement de la densité d'états de phonons du système.

Abstract
Mössbauer spectra were obtained for ¹²⁵Te enriched tellurium films ~ 2 µm thick. The films were prepared in an amorphous form by careful evaporation in a vacuum onto cooled copper substrates. The amorphous films were crystallized in situ by warming to room temperature. The spectrum of the polycrystalline film is quite similar to that obtained in powders [1] except for a rather pronounced asymmetry in the strengths of the quadrupole doublet components. The asymmetry is entirely due to a preferred crystalline orientation such that the [0001] axis is perpendicular to the substrate [2, 3]. In the amorphous film, the asymmetry between the intensities of the quadrupole doublet lines remains, the recoil-free-fraction is diminished by a factor of about three, and there is a slight increase in the quadrupole splitting. Despite the apparent orientation effect in the amorphous phase, the sample can be shown to be truly amorphous in the usual sense of exhibiting no long range order. The increase in the quadrupole splitting when the sample is amorphous can be correlated with a slight decrease in the lengths of the covalent bonds along the spiral chain of Te atoms [4]. The Mössbauer results are compared with the results of experiments by others on amorphous Te using Raman scattering, electron diffraction, and photoemission spectroscopy techniques.