Novel liquid-liquid transition in the liquid Se-GeSe system

Department of Physics, Faculty of Science, Niigata University, Ikarashi 2-8050, Nishi-ku, Niigata 950-2181, Japan

Abstract

The sound velocity in the liquid Se-SeGe system under the saturated vapor pressure was measured at every 1 degree. A minimum in the sound velocity as a function of temperature has been observed for alloys with 12.5 to 45 at.% Ge, which suggests that the crossover liquid-liquid transition occurs in the liquid around GeSe₂. In addition to the minimum, it has been found for alloys with 15 to 27.5 at.% Ge that the sound velocity decreases rather stepwise. The reproducibility has been checked for different samples with the same composition and for different ultrasonic transducers. The decrease occurs in a very narrow temperature interval, a few degrees, and shows hysteresis depending on thermal treatments. The position of this temperature region lowers with increasing Ge concentration, and appears to merge into a minimum in the sound velocity around GeSe₂. Novel structural changes, being the first order in nature, occur slightly below the crossover transition.