Topic
Polyamorphism
About: Polyamorphism is a research topic. Over the lifetime, 588 publications have been published within this topic receiving 29122 citations.
Papers published on a yearly basis
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Papers
TL;DR: In this paper, high energy X-ray diffraction (HEXRD) of supercooled Y2O3 − Al 2O3 liquids and the low frequency vibrational dynamics of recovered glasses were used to investigate the LLPT in this refractory system with emphasis on determining the structure of amorphous materials.
Abstract: Liquids in the system Y2O3 − Al2O3 have been the subject of considerable study because of the reported occurrence of a first-order density and entropy-driven liquid–liquid phase transition (LLPT) in the supercooled liquid state. The observations have become controversial because of the presence of crystalline material that can be formed simultaneously and that can mask the nucleation and growth of the lower density liquid. The previous work is summarized here along with arguments for and against the different viewpoints. Also two studies have been undertaken to investigate the LLPT in this refractory system with emphasis on determining the structure of unequivocally amorphous materials. These include the in situ high energy X-ray diffraction (HEXRD) of supercooled Y2O3 − Al2O3 liquids and the low frequency vibrational dynamics of recovered glasses. Many-body molecular dynamics simulations are also used to interpret the results of both studies. The HEXRD measurements, combined with aerodynamic levitation and rapid data acquisition techniques, show that for the 20 mol% Y2O3 (i.e. AlY20) liquid there is a shift in the position of the first peak in the diffraction pattern over a narrow temperature range (2100–1800 K) prior to crystallization. Microbeam Raman spectroscopy measurements made on AlY20 glasses clearly show contrasting spectra in the low frequency part of the spectrum for low- (LDA) and high-density (HDA) glassy regions. The molecular dynamics simulations identify contrasting coordination environments around oxygen anions for the high- (HDL) and low-density (LDL) liquids.
11 citations
TL;DR: In this paper, high-pressure polyamorphism in amorphous TiO2 (a-TiO2) was investigated and it was shown that the Ti coordination number (CN) increases from 7.2 ± 0.3 at ∼16 GPa to 8.8 ± 0 3 at ∼70 GPa and finally reaches a plateau at 8.9 ± 0.3 at ≲86 GPa.
Abstract: Knowledge of the structure in amorphous dioxides is important in many fields of science and engineering. Here we report new experimental results of high-pressure polyamorphism in amorphous TiO2 (a-TiO2). Our data show that the Ti coordination number (CN) increases from 7.2 ± 0.3 at ∼16 GPa to 8.8 ± 0.3 at ∼70 GPa and finally reaches a plateau at 8.9 ± 0.3 at ≲86 GPa. The evolution of the structural changes under pressure is rationalized by the ratio (γ) of the ionic radius of Ti to that of O. It appears that the CN ≈ 9 plateau correlates with the two 9-fold coordinated polymorphs (cotunnite, Fe2P) with different γ values. This CN-γ relationship is compared with those of a-SiO2 and a-GeO2, displaying remarkably consistent behavior between CN and γ. The unified CN-γ relationship may be generally used to predict the compression behavior of amorphous AO2 compounds under extreme conditions.
11 citations
TL;DR: In this article, a simple model of a glass former fluid, consisting of a bidisperse mixture of penetrable spheres, is studied, and the model shows a transition from fragile to strong behavior as temperature is reduced, driven by the competition between the two mechanisms that contribute to diffusivity in the model.
Abstract: A simple model of a glass former fluid, consisting of a bidisperse mixture of penetrable spheres is studied. The model shows a transition from fragile to strong behavior as temperature is reduced. This transition is driven by the competition between the two mechanisms that contribute to diffusivity in the model: collective rearrangement of particles (responsible for the fragile behavior), and individual particle motion (which gives rise to the strong behavior at low temperature). We also observe a maximum of diffusivity as a function of pressure that can be interpreted within the same framework. The connection between this behavior and polyamorphism is addressed.
11 citations
TL;DR: In this paper, a large enhancement of solid-phase epitaxial growth due to hydrostatic pressure is explained by stress-enhanced self-diffusivity in the amorphous solid.
Abstract: A large enhancement of solid-phase epitaxial growth (SPEG) due to hydrostatic pressure is explained by stress-enhanced self-diffusivity in the amorphous solid. The crystallization is by the adjustment of atomic positions in the vicinity of the crystalline/amorphous (c-a) interface due to self-diffusion in the amorphous phase, assisted by a free-energy decrease equal to the difference in free energies between the amorphous and crystalline phases. Owing to a mismatch in the bulk moduli between the amorphous and crystalline phases, non-hydrostatic stresses are developed near the c-a interface under hydrostatic pressure. Non-hydrostatic stresses in the amorphous layer enhance the mobility of point defects in the amorphous layer. This leads to an increased self-diffusivity in the amorphous layer and, therefore, an enhancement of the SPEG rate.
10 citations
TL;DR: In this article, the thermodynamics of Mott transition in amorphous semiconductors are considered in a framework of field dependent equilibrium free carrier concentration at the lattice temperature, and neither avalanche multiplication or hot electron are assumed.
Abstract: The amorphous semiconductors are assumed to be capable of existing in two distinct thermodynamic states, an insulating state at low temperature and a “metallic” state at high temperature. The thermodynamics of Mott transition is considered in a framework of field dependent equilibrium free carrier concentration at the lattice temperature, and neither avalanche multiplication or hot electron are assumed. The switching effect observed in amorphous semiconductors is analysed as a phenomenon of nucleation and growth of a conducting ‘metallic’ phase. We are considering purely electronic phases, and no irreversible structural rearrangement is assumed involved. The threshold electric field at which insulator-metallic transition is achieved is shown to be a relevant nucleation field. This is thus a phase transition of an electron fluid from low density electron with perfect gas behaviour (insulating state) to a high density liquid behaviour (metallic state).
10 citations
Related Topics (5)
Performance Metrics
| Year | Papers |
|---|---|
| 2025 | 5 |
| 2024 | 11 |
| 2023 | 19 |
| 2022 | 33 |
| 2021 | 21 |
| 2020 | 13 |