Microscopic origin of demixing in Ge20SexTe80−x alloys

Study of the Ge20Te80-xSex glassy structures by combining solid state NMR, vibrational spectroscopies and DFT modelling

“…This trend of the IR response is also expected from the DFT calculations of the asymmetric stretching modes of mixed tetrahedral units. These findings agreed perfectly with the X-ray, neutron diffraction and extended X-ray fine structure (EXAFS) measurements reported by Ratkai et al [15].…”

“…Another statement can be made for tellurium-rich part, if selenium gets into the homopolar chain, the modes between 208 and 211 cm -1 would be shown on the Raman spectra. However, there is no mode at this frequency, the mixed νSe-Te mode should not be present in the Te-rich part of the system in agreement with Ratkai et al [15].…”

“…Either the work focused on a single composition of the Ge-Te-Se ternary system, or on a selenium or tellurium rich part of the system along the pseudo-binary line GeSe 4 -GeTe 4 . [15][16][17][18][19]21,26] However, different assignments of vibration bands have been reported showing the difficulties of interpretations. To interpret these results, the methodology used combine experimental acquisitions (Raman and IR) and DFT calculations on selected clusters to help in the assignment of the vibrational modes observed.…”

“…Moreover, some Se atoms in the model are shared by two Ge(Te, Se) 4 tetrahedra without forming Te-Se bonds. To go further using the same approach, Ratkai et al [15] have tried to understand the presence of the non-mixing zone for Ge 20 Se 80-x Te x (x = 75, 70, 65, 60) glasses. They suggested that for lower Se concentration, the structure can be described as essentially built up of GeTe 4 tetrahedra connected to each other by Te-Te dimers.…”

Structural, electronic and kinetic properties of the phase-change material Ge2Sb2Te5 in the liquid state

“…For standard generalized-gradient-approximation (GGA) functionals, the main discrepancy is the fact that the bond distances in liquid and amorphous PCMs are typically overestimated by 1–3%. A number of studies, including some of our own works12133334353637, have shown that the complementary information provided by different experimental techniques such as X-ray diffraction (XRD), neutron diffraction (ND) and extended X-ray absorption fine structure (EXAFS) can be effectively combined and interpreted in the frame of the reverse Monte-Carlo (RMC) simulation method38. In particular, in refs 12,13, the RMC method was used to analyse XRD, ND and EXAFS data for amorphous Ge 1 Sb 2 Te 4 and Ge 2 Sb 2 Te 5 alloys.…”