The valence transition in SmSe

Abstract

Introduction The Sm monochalcogenides, which crystallize in the NaCl crystal structure, undergo pressure-induced mixed valence transitions. These isostructural phase transitions are of first order in SmS and continuous in SmSe and SmTe. It has been suggested’ that these transitions may all be of first order at low enough temperature. Thus we investigated the valence transition at 77K in order to observe a possible sharpening. Another reason for the low-temperature work was the reduction of the temperature-dependent part of the EXAFS DebyeWailer factor in order to observe better a possible structural disorder. For maximum resolution in R-space we measured the Se K-edge EXAFS up to 24 A-1. While previous work2 already indicated an anomaly in the DebyeWaller factor in the region of the phase transition we now try to determine whether this anomaly can be interpreted as being due to a splitting of the nn Se-Sm distance into two Se-Sm distances according to the different ionic radii of the rare earth ion.