<i>Ab initio</i>phase stability at high temperatures and pressures in the V-Cr system

Landa, A.; Söderlind, Per; Yang, Lin

doi:10.1103/physrevb.89.020101

Cited by 14 publications

(21 citation statements)

References 20 publications

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“…At higher temperatures the bcc phase is recovered as can be seen by the pattern measured at 64 GPa and 1840 K (notice that the three peaks of V are sharp again). This observation is consistent with both the predictions made by Wang et al [18] and the calculations of Landa et al [15] who find that bcc-V is stable at 75 GPa and 2500 K. This suggests that the phonon anomalies triggering the rhombohedral lattice distortion in V at HP [31] can be canceled at HT by effects from phonon-phonon scattering [32].…”

Section: Resultssupporting

confidence: 92%

Melting curve and phase diagram of vanadium under high-pressure and high-temperature conditions

et al. 2019

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We report a combined experimental and theoretical study of the melting curve and the structural behavior of vanadium under extreme pressure and temperature. We performed powder x-ray diffraction experiments up to 120 GPa and 4000 K, determining the phase boundary of the bcc-to-rhombohedral transition and melting temperatures at different pressures. Melting temperatures have also been established from the observation of temperature plateaus during laser heating, and the results from the density-functional theory calculations. Results obtained from our experiments and calculations are fully consistent and lead to an accurate determination of the melting curve of vanadium. These results are discussed in comparison with previous studies. The melting temperatures determined in this study are higher than those previously obtained using the speckle method, but also considerably lower than those obtained from shock-wave experiments and linear muffin-tin orbital calculations. Finally, a high-pressure high-temperature equation of state up to 120 GPa and 2800 K has also been determined.

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Section: Resultssupporting

confidence: 92%

Melting curve and phase diagram of vanadium under high-pressure and high-temperature conditions

et al. 2019

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“…As was mentioned in ref [107], the lattice vibrations at elevated temperatures promote recovery of the BCC structure of compressed vanadium at elevated temperatures. A similar mechanism of phase transformation (based on the vibrational entropy contribution to the Gibbs free energy) is appropriate for vanadium nitride (VN), which at ambient conditions exists in the rock-salt (B1) structure [110].…”

Section: Discussionmentioning

confidence: 59%

“…This investigation affirms that the Kohn anomaly (the FS nesting) and phonon (the shear modulus) softening can easily be suppressed by appropriate alloying. However, the compression-induced mechanical instability of BCC V, which results in formation of the rhombohedral phase close to 600-700 kbar at ambient temperature, will survive significant heating and compression [90,107]. Utilizing the self-consistent ab intio lattice dynamics approach, Landa et al [107] have found that the Rh phase of vanadium remains stable under heating up to~2500 K at early onset of the BCC → Rh transition (740 kbar).…”

Section: Discussionmentioning

confidence: 99%

“…However, the compression-induced mechanical instability of BCC V, which results in formation of the rhombohedral phase close to 600-700 kbar at ambient temperature, will survive significant heating and compression [90,107]. Utilizing the self-consistent ab intio lattice dynamics approach, Landa et al [107] have found that the Rh phase of vanadium remains stable under heating up to~2500 K at early onset of the BCC → Rh transition (740 kbar). This temperature of destabilization (stabilization) of the Rh (BCC) phase is significantly below the shock melting temperature of BCC vanadium, T m~4 000 K [108], as well as below the static (DAC) melting temperature, T m~2 650 K [109].…”

Section: Discussionmentioning

confidence: 99%

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Kohn Anomaly and Phase Stability in Group VB Transition Metals

et al. 2018

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Abstract:In the periodic table, only a few pure metals exhibit lattice or magnetic instabilities associated with Fermi surface nesting, the classical examples being α-U and Cr. Whereas α-U displays a strong Kohn anomaly in the phonon spectrum that ultimately leads to the formation of charge density waves (CDWs), Cr is known for its nesting-induced spin density waves (SDWs). Recently, it has become clear that a pronounced Kohn anomaly and the corresponding softening in the elastic constants is also the key factor that controls structural transformations and mechanical properties in compressed group VB metals-materials with relatively high superconducting critical temperatures. This article reviews the current understanding of the structural and mechanical behavior of these metals under pressure with an introduction to the concept of the Kohn anomaly and how it is related to the important concept of Peierls instability. We review both experimental and theoretical results showing different manifestations of the Kohn anomaly in the transverse acoustic phonon mode TA (ξ00) in V, Nb, and Ta. Specifically, in V the anomaly triggers a structural transition to a rhombohedral phase, whereas in Nb and Ta it leads to an anomalous reduction in yield strength.

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“…Few study was devoted to finite temperatures. Recently, Landa et al 21. studied the stability of vanadium metal and vanadium-chromium alloys in BCC phase at high temperatures and pressures by calculating the anharmonic phonon dispersions.…”

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confidence: 99%

Stability of rhombohedral phases in vanadium at high-pressure and high-temperature: first-principles investigations

Wang

Wu²,

Chen

et al. 2016

Sci Rep

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The pressure-induced transition of vanadium from BCC to rhombohedral structures is unique and intriguing among transition metals. In this work, the stability of these phases is revisited by using density functional theory. At finite temperatures, a novel transition of rhombohedral phases back to BCC phase induced by thermal electrons is discovered. This reentrant transition is found not driven by phonons, instead it is the electronic entropy that stabilizes the latter phase, which is totally out of expectation. Parallel to this transition, we find a peculiar and strong increase of the shear modulus C44 with increasing temperature. It is counter-intuitive in the sense that it suggests an unusual harding mechanism of vanadium by temperature. With these stability analyses, the high-pressure and finite-temperature phase diagram of vanadium is proposed. Furthermore, the dependence of the stability of RH phases on the Fermi energy and chemical environment is investigated. The results demonstrate that the position of the Fermi level has a significant impact on the phase stability, and follows the band-filling argument. Besides the Fermi surface nesting, we find that the localization/delocalization of the d orbitals also contributes to the instability of rhombohedral distortions in vanadium.

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Ab initiophase stability at high temperatures and pressures in the V-Cr system

Cited by 14 publications

References 20 publications

Melting curve and phase diagram of vanadium under high-pressure and high-temperature conditions

Melting curve and phase diagram of vanadium under high-pressure and high-temperature conditions

Kohn Anomaly and Phase Stability in Group VB Transition Metals

Stability of rhombohedral phases in vanadium at high-pressure and high-temperature: first-principles investigations

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