Raman scattering study of the a-GeTe structure and possible mechanism   for the amorphous-to-crystal transition
  We report on an inelastic (Raman) light scattering study of the local structure of amorphous GeTe films. A detailed analysis of the temperature-reduced Raman spectra has shown that appreciable structural changes occur as a function of temperature. These changes involve modifications of atomic arrangements such as to facilitate the rapid amorphous-to-crystal transformation, which is the major advantage of phase-change materials used in optical data storage media. A particular structural model, supported by polarization analysis, is proposed being compatible with the experimental data as regards both the structure of a-GeTe and the crystallization transition. The remarkable difference between the Raman spectrum of the crystal and the glass can thus naturally be accounted for. 
K. S. Andrikopoulos, S. N. Yannopoulos, G. A. Voyiatzis, A. V.   Kolobov, M. Ribes, and J. Tominaga