Anomalous and normal dependence of the sound velocity in the liquid Bi-Sb system

The sound velocity in selected liquid alloys of the isomorphous Bi-Sb system was measured as a function of temperature to a high accuracy of 0.2%. The sound velocity temperature coefficient, dlnc/dT, at the liquidus is found to vary non-monotonously as a function of alloy composition, with the transition from normal to anomalous temperature dependence occurring at a composition of approximately Bi35Sb65. Beyond this composition up to approximately Bi10Sb90 the sound velocity is found to be temperature independent over a wide range. The deviation of the sound velocity from that expected in an ideal solution is found to be dominated by a sub-regular interaction. The present measurements allow the determination of the pressure dependence of the sub-regular solution interaction parameters and are found to be consistent with high pressure studies of the phase diagram in this system. The sound velocity is shown to be an effective measure of the pressure dependence of the alloy interactions.