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

D. Errandonea, S. G. MacLeod, L. Burakovsky, D. Santamaria-Perez, J. E. Proctor, H. Cynn, and M. Mezouar

Phys. Rev. B 100, 094111 – Published 30 September 2019

Abstract

Melting curve and phase diagram of vanadium under high-pressure and high-temperature conditions 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 body-centered cubic-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 shockwave 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.

Received 14 August 2019
Revised 13 September 2019

DOI:https://doi.org/10.1103/PhysRevB.100.094111

Physics Subject Headings (PhySH)

Crystal melting Pressure effects

X-ray powder diffraction

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

D. Errandonea ¹, S. G. MacLeod^2,3, L. Burakovsky⁴, D. Santamaria-Perez¹, J. E. Proctor^3,*, H. Cynn⁵, and M. Mezouar⁶

¹Departamento de Física Aplicada-ICMUV, Universidad de Valencia, MALTA Consolider Team, Edificio de Investigación, C/Dr. Moliner 50, 46100 Burjassot, Valencia, Spain
²Atomic Weapons Establishment, Aldermaston, Reading, RG7 4PR, United Kingdom
³SUPA, School of Physics and Astronomy, and Centre for Science at Extreme Conditions, The University of Edinburgh, Edinburgh, EH9 3FD, United Kingdom
⁴Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
⁵Physics Division, Lawrence Livermore National Laboratory, Livermore, California 94550, USA
⁶ID27 Beamline, European Synchrotron Radiation Facility, 71 Avenue des Martyrs, 38000 Grenoble, France

^*Present address: School of Computing, Science, and Engineering, University of Salford, Manchester M5 4WT, United Kingdom.

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Issue

Vol. 100, Iss. 9 — 1 September 2019

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Images

Figure 1
XRD patterns at selected pressures and temperatures (indicated in the figure). In the two lowest traces, experiments are shown with symbols and Rietveld refinements and residuals are shown with solid lines. The ticks correspond to positions of V peaks. The splitting of V peaks due to the rhombohedral distortion can be clearly seen. All peaks are labeled (V peaks in a different color to facilitate the identification). W identifies peaks from tungsten and $B 1$ and $B 2$ peaks from the different phases of NaCl. bcc and Rh are used to identify the bcc and rhombohedral phases.
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Figure 2
XRD patterns for a heating run at 32 GPa. The peaks of V, W, and $B 2$ NaCl are identified. Temperatures are given in the figure. The pattern measured at 2790 K corresponds to a temperature where permanent recrystallization of V is observed.
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Figure 3
Zooming in on the region of the XRD patterns measured at 32 GPa to illustrate the disappearance of the (110) peak of V and the increase of the background. Temperatures are indicated in the figure.
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Figure 4
Corresponding temperature plateau in the temperature vs laser power plot for the melting point at 40 GPa. The red line represents the melting temperature.
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Figure 5
P-T phase diagram of V. White circles: bcc V. Blue triangles: rhombohedral V. Upside-down pink triangle: rhombohedral V from Ref. [17]. Blue dashed line is the tentative bcc-rhombohedral phase boundary based upon present and previous studies [19, 21]. White star represents the bcc stability point calculated by Landa et al. [15]. Green circles are the points where rapid recrystallization is observed. Pink circles are the melting points determined from present synchrotron experiments. Pink squares are the melting points determined from temperature plateaus. The pink line is the Simon-Glatzel fit to the present melting results. Orange line and diamonds is the calculated melting curve using the $Z$ method. Green asterisks belong to the Hugoniot measured by McQueen and Marsh [41] and red crosses to the Hugoniot measured by Foster et al. [42]. Green dotted line is our calculated Hugoniot. White diamonds are the Hugoniot points measured by Dai et al. [16]. Black diamonds are the melting points determined by the same authors in SW experiments, and the black line is the melting curve proposed by them. Black squares are the DAC melting results from Mainz group [1]. Black star is the melting point calculated by Landa et al. [15].
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Figure 6
Pressure evolution of the unit-cell volume per formula unit (f.u.) for different isotherms identified by colors (temperatures are indicated in the figure). Circles correspond to the bcc phase and diamonds to the rhombohedral phase. The results at 1000 K were taken from Ref. [50]. The solid lines correspond to the P-V-T EOS reported here.
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