Far-infrared Spectra of the Chalcogenide Alloy of the GST System of Composition Ge15Sb15Te70 in the Glassy and Crystalline State

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.