Far-infrared spectra of the chalcogenide alloy of the GST system of composition Ge15Sb15Te70 in the glassy and crystalline states have been measured and analysed in the frequency range of 20–400 cm-1 at room temperature. The absorption in this range is due to the phonon modes of the structural units of crystalline and correlated librational vibrations (boson peak) of glassy alloy, which precede the appearance of relaxation dynamics. IR spectroscopy is one of the most frequently used spectroscopic tools for the crystals and amorphous materials (including chalcogenide) study The vibrational assignments of various absorption bands and the differences revealed in the spectra will make it possible to more confidently elucidate the possible molecular mechanism of the crystal-to-amorphous transition in other chalcogenide alloys. New details of the crystal-to-amorphous transition scenario are suggested. The results, by the example of the composition Ge15Sb15Te70, demonstrate, that the use of far-IR spectroscopy has a clear potential to characterise the local atomic structure and dynamics of the GST alloys. Here experimental evidence is present that along with the change in bonding mechanism there is change medium-range ordering upon crystallisation in GST alloys. Further studies on the new GST materials will give the possibility to improve the parameters of the already developed memory elements and will provide additional information about the nature of the switching effect.
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