ELASTIC PROPERTIES OF SUPERCONDUCTING CHEVREL-PHASE COMPOUNDS

We present elastic constant and magnetic data for the two Chevrel-phas e compounds PbMo6S8 and Eu0.6Sn0.4Mo6S8Br0.1. A strong softening in th e elastic constants as a function of temperature is observed for the l ongitudinal arid transverse modes in both compounds in the normal Stat e. This effect can be explained with a deformation potential coupling, We find no structural transition in the temperature range 1.2-300 K. In the superconducting regime the attenuation and sound velocity exhib it pronounced anomalies which can be explained using the so-calIed the rmally assisted flux flow model, These data together with electrical r esistivity measurements enable us to construct a detailed B-T phase di agram.