Syste`me AsGeTe

Precession Electron Diffraction – a versatile tool for the characterization of Phase Change Materials

“…6b and 6c, top). These metrics are characteristic for structure models related to GST 629 [28] and GAT 427 [22] and are nominated as GBT 629 (space group: R-3m, a = 4.175 Å, c = 93.677 Å) and GBT 427 (space group: R-3m, a = 4.171 Å, c = 72.847 Å) in the following. The metrics are consistent with the measured distances between consecutive lines of bright spots representing the vacancy layers.…”

“…These metrics, particularly the eightfold increase of c with respect to the rock salt type structure, are consistent with the structure type reported for Ge 5 As 2 Te 8 ("GAT 528"). The atomic coordinates of GAT 528 [22] were applied for the interpretation of the electron microscopy results by simulations. Unfortunately, the sizes of the ordered domains were not sufficient to determine the composition of this component reliably.…”

“…Following the concept of a homologous series of structures, the PCM can be described by hexagonal layers of atoms which are stacked similarly to the rock salt type structure. For example the material with the composition Ge 3 Sb 2 Te 6 (n = 3, m = 1), which should be isostructural to the already studied material Ge 3 As 2 Te 6 [22,23] is assumed to have the following stacking sequence: Te-Sb-Te-Ge-Te-Ge-Te-Ge-Te-Sb-Te. The repetition of this sequence leads to neighboring Te-layers which enhances the stability of the structure [24].…”

Theoretical prediction of the structural, electronic, mechanical and thermodynamic properties of the binary α-As 2 Te 3 and β-As 2 Te 3

“…Scheidemantel et al [18,19] revealed a pressure induced structural phase transition from α-As 2 Te 3 (monoclinic) to β-As 2 Te 3 (rhombohedral) near 7 GPa, leading to dramatic enhancement in its thermoelectric power. Further experimental work has suggested that quenching procedures are sufficient to directly synthesize bulk samples of β-As 2 Te 3 [20].…”

“…As (6c) (0, 0, 0.3967) As (6c) (0, 0, 0.4036) Te (3a) (0, 0, 0) Te (3a) (0, 0, 0) Te (6c) (0, 0 , 0.2140) Te (6c) (0, 0 , 0.2147) Lattice Parameters a=4.062 Å a=4.058 Å [29] c=28.68 Å c=29.59 Å Table 2. The calculated elastic constants ij C (in GPa) of α-and β-As 2 Te 3 .…”