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- Landa, A., et al.
(author)
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Ab initio calculations of elastic constants of the bcc V-Nb system at high pressures
- 2006
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In: Journal of Physics and Chemistry of Solids. - : Elsevier BV. - 0022-3697 .- 1879-2553. ; 67:10-sep, s. 2056-2064
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Journal article (peer-reviewed)abstract
- First-principles total energy calculation based on the exact muffin-tin orbital and full-potential linear muffin-tin orbital methods were used to calculate the equation of state and shear elastic constants of bcc V, Nb, and the V95Nb05 disordered alloy as a function of pressure up to 6 Mbar. We found a mechanical instability in C-44 and a corresponding softening in C at pressures similar to 2 Mbar for V. Both shear elastic constants show softening at pressures similar to 0.5 Mbar for Nb. Substitution of 5 at% of V with Nb removes the instability of V with respect to trigonal distortions in the vicinity of 2 Mbar pressure, but still leaves the softening of C-44 in this pressure region. We argue that the pressure-induced shear instability (softening) of V (Nb) originates from the electronic system and can be explained by a combination of the Fermi surface nesting, electronic topological transition, and band Jahn-Teller effect.
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| 2. |
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| 3. |
- Landa, A., et al.
(author)
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Alloying-driven phase stability in group-VB transition metals under compression
- 2010
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 82:14, s. 144114-
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Journal article (peer-reviewed)abstract
- The change in phase stability of group-VB (V, Nb, and Ta) transition metals due to pressure and alloying is explored by means of first-principles electronic-structure calculations. It is shown that under compression stabilization or destabilization of the ground-state body-centered-cubic (bcc) phase of the metal is mainly dictated by the band-structure energy that correlates well with the position of the Kohn anomaly in the transverse-acoustic-phonon mode. The predicted position of the Kohn anomaly in V, Nb, and Ta is found to be in a good agreement with data from the inelastic x-ray or neutron-scattering measurements. In the case of alloying the change in phase stability is defined by the interplay between the band-structure and Madelung energies. We show that band-structure effects determine phase stability when a particular group-VB metal is alloyed with its nearest neighbors within the same d-transition series: the neighbor with less and more d electrons destabilize and stabilize the bcc phase, respectively. When V is alloyed with neighbors of a higher (4d- or 5d-) transition series, both electrostatic Madelung and band-structure energies stabilize the body-centered-cubic phase. The opposite effect (destabilization) happens when Nb or Ta is alloyed with neighbors of the 3d-transition series.
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| 4. |
- Landa, A., et al.
(author)
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Fermi surface nesting and pre-martensitic softening in V and Nb at high pressures
- 2006
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In: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 18:22, s. 5079-5085
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Journal article (peer-reviewed)abstract
- First-principles total-energy calculations were performed for the trigonal shear elastic constant (C-44) of body-centred cubic (bcc) V and Nb. A mechanical instability in C44 is found for V at pressures of similar to 2 Mbar which also shows a softening in Nb at pressures of similar to 0.5 Mbar. We argue that the pressure-induced shear instability (softening) of V (Nb) is due to the intra-band nesting of the Fermi surface.
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