Anharmonic and Anomalous Trends in the High-Pressure Phase Diagram of Silicon

Paul, R.; Hu, S. X.; Karasiev, Valentin V.

doi:10.1103/physrevlett.122.125701

Cited by 18 publications

(6 citation statements)

References 83 publications

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“…Although the quantum mechanics ab initio simulations paved a promising way for researches on the properties from the atomic scale [3][4][5][6] and progress has been achieved in predicting the structural stability by the global optimization algorithms [7][8][9][10][11] that commonly adopt the criteria of potential energy or enthalpy obtained by electronicstructure computations within the Born-Oppenheimer approximation at T = 0K, it remains a challenge to precisely describe the realistic scenarios at finite temperatures [12,13], in the cases of which the thermodynamic effects have to be taken into account due to nucleus vibrations [14] and the free energy (FE) that incorporates additional kinetic energy and entropy is the very criterion to determine the equilibrium structural phase [15]. Based on ab initio computations, the phonon model within the quasi-harmonic approximation is widely used in order to include the thermal contributions to the FE [16][17][18][19][20] while the model would still produce unsatisfactory results of thermal expansion coefficient or conductivity [21][22][23][24].…”

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confidence: 99%

Thermal contributions to the structural phase transitions of crystalline aluminum under ultrahigh pressures

Ning¹,

Zhang²

2022

Preprint

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The ab initio computation of thermodynamic properties of condensed matters under extreme conditions is a long-time pursuit. In this work, the pressure induced structural phase transition of crystalline aluminum up to 600 GPa at room temperature is investigated by the criterion of free energy derived directly from the partition function formulated in ensemble theory with the interatomic interactions characterized by density functional theory computations. The transition pressures of the FCC→HCP→BCC phase transition are determined at 194 and 361 GPa, the axial ratio of the HCP structure is found to be equal to 1.62 and the discontinuities in the equations of states are confirmed to be associated with −0.674% and −0.897% volume changes, which all validate the accuracy of measurements by one of the recent experiments but disagree with the observations by others. Compared with the results obtained by the widely used criterion of enthalpy at 0K, this work shows that the thermal contributions play a nontrivial role for the structural stability of aluminum even under a room-temperature circumstance.

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confidence: 99%

Thermal contributions to the structural phase transitions of crystalline aluminum under ultrahigh pressures

Ning¹,

Zhang²

2022

Preprint

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“…If phase transitions occur in shock compressed boron at the same pressure-temperature conditions as those expected by the equilibrium phase diagram, the Hugoniot would have two major discontinuities, one at 15 GPa and the other at 80 GPa, corresponding to the phase boundaries of α-B 12 ↔γ-B 28 and γ-B 28 ↔α-Ga, respectively. Following the DFT-based structural equilibrium picture, melting along the Hugoniot occurs for the α-Ga phase at 2500-3500 K and 200 GPa, unless some other unknown structure stabilizes over α-Ga at 100 GPa and 2000 K, which is not unlikely considering the fact that high temperature phases can be stabilized by high pressure in other elemental systems such as beryllium [36] and silicon [37].…”

Section: Resultsmentioning

confidence: 99%

Phase transformation in boron under shock compression

Zhang,

Whitley,

Ogitsu

2020

Preprint

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Boron HugoniotPressure (GPa) Density (g/cm 3 ) Marsh,1980 Le Pape,2013 α-B12 β-B106 γ-B28 α-Ga liq.(γ-B28) liq.(α-Ga) Using first-principles molecular dynamics, we calculated the equation of state and shock Hugoniot of various boron phases. We find a large mismatch between Hugoniots based on existing knowledge of the equilibrium phase diagram and those measured by shock experiments, which could be reconciled if the α-B 12 /β → γ-B 28 transition is significantly over-pressurized in boron under shock compression. Our results also indicate that there exists an anomaly and negative Clapeyron slope along the melting curve of boron at 100GPa and 1500-3000 Kelvin. These results enable in-depth understanding of matter under shock compression, in particular the significance of compressionrate dependence of phase transitions and kinetic effects in experimental measurements.

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“…Figure a shows the calculated Gibbs free energy for bulk Si-I, II, XI, and V phases (solid lines) at T = 300 K from ref (Si-II as the reference), in which Si-II has the lowest free energy between 12 and 14 GPa, and Si-XI and Si-V are the most stable phases between 14–16 and 16–33 GPa, respectively. As a consequence, Si goes through a phase transition sequence of Si-I → II → XI → V (shown by the black dotted line) under compression, consistent with experimental results.…”

Section: Discussionmentioning

confidence: 99%

“…(a) Calculated Gibbs free energy for bulk Si-I (solid blue line), II (solid green line), XI (solid orange line), and V (solid red line) phases at T = 300 K from ref (Si-II as the reference). Schematic diagram of the phase transition paths in bulk Si (black dotted line), SiNWs (pink dash-dotted line), and small SiNPs (purple dashed line) are also combined with the simulation results.…”

Section: Discussionmentioning

confidence: 99%

Pressure-Induced Phase Transitions in Nanostructured Silicon

et al. 2020

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Pressure-induced phase transitions in various nanostructured Si have been studied extensively but still remain not well-understood. In this study, we systematically investigated the phase transitions in nanostructured Si with different sizes and morphology including large and small Si nanoparticles (SiNPs), Si nanowires (SiNWs), and porous Si using in situ high-pressure synchrotron X-ray diffraction and Raman microscopy. The large SiNPs show high-pressure behavior similar to bulk Si, while in the other three samples, the pressure of the first phase transition during compression is elevated. For small SiNPs and porous Si, the initial diamond cubic Si directly transforms to the simple hexagonal phase at ∼16.4 and ∼18.4 GPa during compression (instead of the β-Sn phase in bulk Si), respectively, and amorphous Si was obtained for both samples upon decompression. For SiNWs, the initial diamond cubic Si directly transforms to the Imma phase when compressed to ∼15.2 GPa, and a mixture of amorphous Si and a body-centered cubic phase was obtained upon decompression. Although seemingly diverse behavior was observed, our analysis reveals a unified picture for the various samples, i.e., phase transitions in nanostructured Si are mainly controlled by their domain size, while their morphology has a minor effect. The higher phase-transition pressure and the different phase-transition sequences in the small SiNPs, SiNWs, and porous Si during compression can mainly be attributed to the higher kinetic barrier of phase transformation in nanostructured Si.

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Anharmonic and Anomalous Trends in the High-Pressure Phase Diagram of Silicon

Cited by 18 publications

References 83 publications

Thermal contributions to the structural phase transitions of crystalline aluminum under ultrahigh pressures

Thermal contributions to the structural phase transitions of crystalline aluminum under ultrahigh pressures

Phase transformation in boron under shock compression

Pressure-Induced Phase Transitions in Nanostructured Silicon

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