Sound Velocity in Liquid and Glassy Selenium

TL;DR

This study measures the speed of longitudinal and shear sound waves in liquid, supercooled, and amorphous selenium across different temperature regions, revealing changes in sound velocity associated with phase transitions and the glass transition.

Contribution

It provides detailed measurements of sound velocities in selenium near the glass transition, highlighting hysteresis and velocity anomalies that suggest general properties of the glass transition.

Findings

Sound velocity changes sharply at the glass transition temperature.

Hysteresis observed in sound velocities during heating and cooling.

Distinct regions identified with different relaxation times and phase states.

Abstract

The speed of longitudinal sound waves at 7 and 22 MHz has been measured in liquid, supecooled, and amorphous selenium, including the region around the glass transition temperature, Tg, near 35 C. In amorphous selenium the speed of shear waves at 7 MHz was also measured. The experiments were performed with high purity Se (99.9999%) hermetically sealed in an evacuated quartz ampoule. Four temperature regions with strongly different relaxation times can be distinguished between room temperature and the melting point: (1) a glassy state below Tg, which is stable on the time scale of the experiments, (2) a glassy state above Tg,, which is metastable on the time scale of the experiments, (3) a region where homogeneous crystal nucleation occurs, and (4) a supercooled liquid, which is stable on the time scale of the experiments. Each region is marked by a change in the slope of the temperature dependence of the sound velocity. Near the glass transition temperature the velocities of longitudinal and transverse sound exhibit hysteresis with a step-like drop on heating and a more continuous rise on cooling. The step-like anomaly in sound velocity may be a general property of the glass transition.