We computed the Raman spectrum of cubic and amorphous Ge2Sb 2Te5 (GST) by ab initio phonons and an empirical bond polarizability model. Models of the amorphous phase were generated by quenching from the melt by means of ab initio molecular dynamics simulations. The calculated spectra are in good agreement with experimental data which confirms the reliability of the models of the amorphous phase emerged from the simulations. All the features of the spectrum in both crystalline and amorphous GST can be assigned to vibrations of defective octahedra. The calculations reveal that the polarizability of the Sb-Te is much higher than that of Ge-Te bonds and of Ge-Ge/Sb wrong bonds resulting in a much lower Raman response of tetrahedra which are made of Ge-Te and wrong bonds. As a consequence and as opposed to amorphous GeTe, the signatures of tetrahedra in the Raman spectrum of amorphous GST are hidden by the larger Raman cross section of defective octahedra.
Sosso, G., Caravati, S., Mazzarello, R., Bernasconi, M. (2011). Raman spectra of cubic and amorphous Ge{2}Sb{2}Te{5} from first principles. PHYSICAL REVIEW. B, CONDENSED MATTER AND MATERIALS PHYSICS, 83(13), 134201 [10.1103/PhysRevB.83.134201].
Raman spectra of cubic and amorphous Ge{2}Sb{2}Te{5} from first principles
BERNASCONI, MARCO
2011
Abstract
We computed the Raman spectrum of cubic and amorphous Ge2Sb 2Te5 (GST) by ab initio phonons and an empirical bond polarizability model. Models of the amorphous phase were generated by quenching from the melt by means of ab initio molecular dynamics simulations. The calculated spectra are in good agreement with experimental data which confirms the reliability of the models of the amorphous phase emerged from the simulations. All the features of the spectrum in both crystalline and amorphous GST can be assigned to vibrations of defective octahedra. The calculations reveal that the polarizability of the Sb-Te is much higher than that of Ge-Te bonds and of Ge-Ge/Sb wrong bonds resulting in a much lower Raman response of tetrahedra which are made of Ge-Te and wrong bonds. As a consequence and as opposed to amorphous GeTe, the signatures of tetrahedra in the Raman spectrum of amorphous GST are hidden by the larger Raman cross section of defective octahedra.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.