Thermal diffusivity of Ge-Te glass near the glass-supercooled-liquid transition

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Abstract
The measurement of the thermal diffusivity DT of the glassy Ge20Te80 alloy obtained by rapid quenching from the melt was carried out using a ruby laser flash technique. A glass-supercooled-liquid transition was manifested by a lambda -form in DT, as the alloy was heated from room temperature to around 200 degrees C. Thus the thermal and hydrodynamic evidence of the transition was observed, for the first time, for the amorphous semiconducting and metallic materials within a narrow temperature range around the glass transition temperature. The crystalline-to-amorphous phase transformation in the Ge-Te alloy gave rise to an abrupt fall in DT for the semiconducting Ge20Te80 glass (i.e., 2.0*10-3 approximately 5.5*10-3 cm2 s-1), which is very small compared to that (around 1.5*10-2 cm2 s-1) for the crystalline Te+GeTe mixture. Since DT in the first approximation is proportional to the electron mean free path, it may become short and the conduction process can be regarded as strong scattering of electrons in the glass. The production of the metastable crystalline solid in the equilibrium phase consisting of the crystalline Te and GeTe solids was confirmed by the sharp Bragg-type maxima observed in the X-ray scattering from the Ge20Te80 glass heated above the crystallisation temperature and by the experimental data on DT for the same sample.