TE-125 MOSSBAUER-SPECTROSCOPY STUDY OF SOME RARE-EARTH MONOTELLURIDE BASED SOLID-SOLUTIONS

Mossbauer spectroscopy is a very suitable method to study very weak mo difications of electronic states in the valence band. It probes the lo cal environment of the central atom. The isomer shift (delta) measures the s electron density on the nucleus and the quadrupolar interaction (Delta) is an indicator of the asymmetry of the electron distribution . The line width (Gamma) of the Mossbauer absorption provides details about the order and site distribution in the material. Yb1-xEuxTe, Pb1 -xEuxTe and Yb1-xGdxTe are f.c.c. solid solutions. They exist for 0 le ss than or equal to x less than or equal to 1. In these systems, with the exception of the trivalent gadolinium ion, all the cations are div alent. Te is in its divalent state. Eu2+ and Gd3+ carry a magnetic mom ent. All the other ions are non magnetic. YbTe and EuTe are large gap semiconductors; PbTe is a small gap one and GdTe is a metal. So, these solid solutions allow us to study the dilution of magnetism without a ny evolution of the nature of the ionic bond (Yb(Eu)Te), in a presence of a variation of the ionic character of the bond (Pb(Eu)Te) and in c orrelation with a semiconductor-metal transition (Yb(Gd)Te). These sys tems have been characterised by Te-125 Mossbauer spectroscopy. The x-d ependence of the Mossbauer parameters is discussed with respect to the variation of the physical properties with composition in the differen t solid solutions.