Abstract
A typical binary amorphous telluride GeTe2 is investigated from first-principles molecular dynamics simulations. After a comparison with chemical analogs from neutron or X-ray diffraction experiments, such as GeO2 or GeSe2, the structure of this material is studied by examining real and reciprocal space properties. It is found that the base geometrical motifs of the germanium atom can be either in tetrahedral or in defected coordinations involving pyramidal units. A review of previous results for other compositions reveals that such binary Ge tellurides contain soft tetrahedra, at variance with lighter chalcogenides, such as Ge-S and Ge-Se, and are characterized by an increased angular bending motion (typically 20°) as compared with, e.g., Ge-S (5°). In addition, for amorphous Ge-rich materials, GeTe2 and GeTe, a secondary tetrahedral geometry appears, related to the presence of Ge-Ge bonds, having a larger mean angle of about 125°. These typical features not only relate to characteristics observed from scattering experiments but may also be a crucial feature for the understanding of the phase-change phenomena..