Ultrasonic velocities and thermal expansion coefficients of amorphous Se80Te20 and Se90Te10 alloys near glass transitions

Precise measurements of the ultrasonic velocities and thermal expansivities of amorphous Se₈₀Te₂₀ and Se₉₀Te₁₀ alloys are reported near the glass transition. The samples are produced by liquid quenching. The longitudinal and transverse velocities are measured at 10 MHz frequency using the McSkimin pulse superposition technique. The thermal expansivities,, are measured using a three-terminal capacitance bridge. The-values show a sharp maximum near the glass transition temperature,T _g. The ultrasonic velocities also show a large temperature derivative, dV/dT nearT _g. The data are discussed in terms of existing theories of the glass transition. The continuous change in shows that the glass transition is not a first-order transition, as suggested by some theories. The samples are found to be deformed by small loads nearT _g. The ultrasonic velocities and dV/dT have contributions arising from this deformation.