This title appears in the Scientific Report : 2020 

Phase change memory materials: Rationalizing the dominance of Ge/Sb/Te alloys
Jones, Robert O. (Corresponding author)
Quanten-Theorie der Materialien; IAS-1
Quanten-Theorie der Materialien; PGI-1
Physical review / B covering condensed matter and materials physics, 101 (2020) 2, S. 024103
Woodbury, NY Inst. 2020
Journal Article
Density functional calculations with molecular dynamics -- amorphous and crystalline materials
Controlling Configuration-Based Phenomena
Controlling Spin-Based Phenomena
Please use the identifier: in citations.
Please use the identifier: in citations.
Rewritable optical storage is dominated by alloys of a small number of elements, overwhelmingly Ge, Sb, and Te. For over 30 years, Ge/Sb/Te alloys in the composition range (GeTe)1−x(Sb2Te3)x(0≤x≤1) have been the materials of choice in commercial devices: all have metastable rock-salt structures that change little over decades at archival temperatures, and all contain vacancies (cavities). The special status of Ge/Sb/Te alloys arises from the close similarity of their valence orbitals as measured by the orbital radial moments, so that bonds are stronger than in other combinations of elements of groups 14–16 with appropriate valences. The orbital similarity arises from the irregular changes in atomic orbitals and properties as the atomic number increases (“secondary periodicity”). Jones showed [P. R. Soc. London, Ser. A 147, 396 (1934)] that the simple cubic structure of (metallic) Bi (valence configuration 6s26p3) is unstable to a distortion to a (semimetallic) rhombohedral structure. This picture can be adapted to Ge/Sb/Te alloys to explain the metastable structure of the above family of compounds where vacancies almost always occur next to Te atoms, which form one sublattice of the rock-salt structure. The disorder in the Ge/Sb/vacancy sublattice is not random.