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Structural and calorimetric investigation of GexTe100-x films over wide range of concentration 10 < x < 50 led to evidence two structural singularities at x ~ 22 at. % and x ~ 33-35 at. %. Analysis of bond distribution, bond variability, and glass thermal stability led to conclude to the origin of the first singularity being the flexible/rigid transition proposed in the framework of rigidity model and the origin of the second one being the disappearance of the undercooled region resulting in amorphous materials with statistical distributions of bonds. While the first singularity signs the onset of the Ge-Ge homopolar bonds, the second is related to compositions where enhanced Ge-Ge correlations at intermediate lengthscales (7.7 Å) are observed. These two threshold compositions correspond to recently reported resistance drift threshold compositions, an important support for models pointing the breaking of homopolar Ge-Ge bonds as the main phenomenon behind the ageing of phase change materials. [ABSTRACT FROM AUTHOR]

Amorphous chalcogenides usually exhibit a resistivity, which increases with age following a power law ρ~tα. Existing theories link this change in amorphous state resistivity to structural relaxation. Here, the impact of fundamental glass properties on resistance drift phenomena in amorphous GexTe1-x networks is studied. Employing Raman spectroscopy, the Maxwell rigidity transition from flexible to stressed rigid is determined to occur in the compositional range 0.2500.265) exhibit rather strong resistance drift, where the drift parameters increase steadily from α=0.13 for amorphous GeTe to α=0.29 for compositions near the stiffness threshold xc. On the other hand, the drift parameter in flexible glasses (x<0.25) decreases with decreasing Ge content x to values as low as α=0.05. These findings illustrate the strong impact of the stiffness threshold on resistance drift phenomena in chalcogenides. [ABSTRACT FROM AUTHOR]

Aging is a ubiquitous phenomenon in glasses. In the case of phase-change materials, it leads to a drift in the electrical resistance, which hinders the development of ultrahigh density storage devices. Here we elucidate the aging process in amorphous GeTe, a prototypical phase-change material, by advanced numerical simulations, photothermal deflection spectroscopy and impedance spectroscopy experiments. We show that aging is accompanied by a progressive change of the local chemical order towards the crystalline one. Yet, the glass evolves towards a covalent amorphous network with increasing Peierls distortion, whose structural and electronic properties drift away from those of the resonantly bonded crystal. This behaviour sets phase-change materials apart from conventional glass-forming systems, which display the same local structure and bonding in both phases.