Search for a possible flexible-to-rigid transition in models of phase change materials

Micoulaut, Matthieu; Flores‐Ruiz, Hugo M.

doi:10.1103/physrevb.103.134206

Cited by 8 publications

(21 citation statements)

References 93 publications

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“…These materials reside in the stressed‐rigid phase of the Ge–Sb–Te ternary that is expected given that in the stressed‐rigid phase, the glass forming tendency is poor and materials have a strong tendency to crystallize. This result has been established from a combination of ab initio MD simulations and MD‐based constraint counting algorithms (Figure 16) along the Ge x Sb x Te 1−2 x join, thus permitting one to identify an isostatic condition (flexible to rigid transition) for x c = 8.5% 134 . Close to this composition and as already anticipated from what is known in Ge–Se on optimal glass‐forming tendency, 146 glasses can be produced in this highly crystallizing Ge–Sb–Te ternary alloy, 147 and now extend the glass‐forming domain that was previously limited to Sb poor compositions close to the GeTe 6 eutectic (cyan‐colored region in Figure 18) and has also been used to develop a successful OTS device 23 …”

Section: Broader Aspectsmentioning

confidence: 84%

“…Calculated constraint density in different chalcogenide glasses as a function of network mean coordination number 〈 r 〉: glassy (blue boxes) and liquid (blue triangles 96 ) Ge–Se, glassy Ge–S (red 132 ), and amorphous Ge–Sb–Te (black boxes 134 ). The broken line represents the mean‐field constraint count n c = 2+5 〈 r 〉/2 29 .…”

Section: Insights From Molecular Dynamics Simulationsmentioning

confidence: 99%

“…It is important to emphasize that systems with a more loose connectedness or a partial breakdown of the octet (8‐N) rule (e.g., Ge–Sb–Te in Figure 16) can be also investigated using such MD‐based constraint counting algorithms 134,135 so that the identified isostatic criterion provides a hint for optimal glass‐forming range. Interestingly, the IP region (〈 r 〉 ≈ 2.4) covering isostatic compositions in Ge–Se manifests by a weak dependence of n c with temperature 96 that also serves to relate the weak dependence of topological degrees of freedom 3 − n c with the weak dependence of liquid viscosity, 108 that is, a minimum in fragility.…”

Section: Insights From Molecular Dynamics Simulationsmentioning

confidence: 99%

“…A phase diagram of Ge–Sb–Te ternary 147 that shows new synthetized glasses along the Ge x Sb x Te 1−2 x join (filled and open red squares) and close to the location of the isostatic condition at x c = 8.5% (yellow point 134 ) investigated by ab initio simulations. The cyan region corresponds to previously Sb‐poor glass compositions around the GeTe6 eutectic.…”

Section: Broader Aspectsmentioning

confidence: 99%

“…To determine BB constraints, partial bond angle distributions are used, and these split the usual bond angle distribution into partial contributions defined by a central F I G U R E 1 6 Calculated constraint density in different chalcogenide glasses as a function of network mean coordination number 〈r〉: glassy (blue boxes) and liquid (blue triangles 96 ) Ge-Se, glassy Ge-S (red 132 ), and amorphous Ge-Sb-Te (black boxes 134 ). The broken line represents the mean-field constraint count n c = 2+5 〈r〉/2.…”

Section: Constraint Countmentioning

confidence: 99%

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Glass transition, topology, and elastic models of Se‐based glasses

et al. 2023

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Features intrinsic to disorder and network aspects are ubiquitous in structural glasses. Among this important class of materials, chalcogenide glasses are special-they are built of short-range covalent forces, making them simpler than silicate glasses that possess mixed ionic and covalent forces. Selenium-based glasses also display complex elastic phase transitions that have been described from various models, including mean-field approaches to molecular simulations. These point to the presence of two sharply defined elastic phase transitions, a rigidity and stress transition that are non-mean-field in character, and separate the three distinct topological phases of flexible, isostatically rigid, and stressedrigid. This article reviews the physics of these glassy networks. The elastic phases and glass transition temperature are explained on a molecular level in terms of topological constraint theory (TCT), connectivity, and the open degrees of freedom. The broader aspects of TCT in relation to phase change materials, high-k dielectrics, and cements are also commented upon.

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Section: Broader Aspectsmentioning

confidence: 84%

Section: Insights From Molecular Dynamics Simulationsmentioning

confidence: 99%

Section: Insights From Molecular Dynamics Simulationsmentioning

confidence: 99%

Section: Broader Aspectsmentioning

confidence: 99%

Section: Constraint Countmentioning

confidence: 99%

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Glass transition, topology, and elastic models of Se‐based glasses

et al. 2023

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Optically Induced Multistage Phase Transition in Coherent Phonon-Dominated a-GeTe

Chen

Lin

Jiang

et al. 2023

J. Phys. Chem. Lett.

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Ultrafast photoexcitation can decouple the multilevel nonequilibrium dynamics of electron–lattice interactions, providing an ideal probe for dissecting photoinduced phase transition in solids. Here, real-time time-dependent density functional theory simulations combined with occupation-constrained DFT methods are employed to explore the nonadiabatic paths of optically excited a-GeTe. Results show that the short-wavelength ultrafast laser is capable of generating full-domain carrier excitation and repopulation, whereas the long-wavelength ultrafast laser favors the excitation of lone pair electrons in the antibonded state. Photodoping makes the double-valley potential energy surface shallower and allows the insertion of A1g coherent forces in the atomic pairs, by which the phase reversal of Ge and Te atoms in the ⟨001⟩ direction is activated with ultrafast suppression of the Peierls distortion. These findings have far-reaching implications regarding nonequilibrium phase engineering strategies based on phase-change materials.

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Unraveling the crystallization kinetics of the Ge2Sb2Te5 phase change compound with a machine-learned interatomic potential

Abou El Kheir,

Bonati,

Parrinello

et al. 2024

npj Comput Mater

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The phase change compound Ge2Sb2Te5 (GST225) is exploited in advanced non-volatile electronic memories and in neuromorphic devices which both rely on a fast and reversible transition between the crystalline and amorphous phases induced by Joule heating. The crystallization kinetics of GST225 is a key functional feature for the operation of these devices. We report here on the development of a machine-learned interatomic potential for GST225 that allowed us to perform large scale molecular dynamics simulations (over 10,000 atoms for over 100 ns) to uncover the details of the crystallization kinetics in a wide range of temperatures of interest for the programming of the devices. The potential is obtained by fitting with a deep neural network (NN) scheme a large quantum-mechanical database generated within density functional theory. The availability of a highly efficient and yet highly accurate NN potential opens the possibility to simulate phase change materials at the length and time scales of the real devices.

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Search for a possible flexible-to-rigid transition in models of phase change materials

Cited by 8 publications

References 93 publications

Glass transition, topology, and elastic models of Se‐based glasses

Glass transition, topology, and elastic models of Se‐based glasses

Optically Induced Multistage Phase Transition in Coherent Phonon-Dominated a-GeTe

Unraveling the crystallization kinetics of the Ge2Sb2Te5 phase change compound with a machine-learned interatomic potential

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