Structural stability of beta-beryllium
2007 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, no 3Article in journal (Refereed) Published
Using density-functional theory formulated within the framework of the exact muffin-tin orbitals method, we investigate the stability of the body-centered-cubic phase of Be (beta-Be). The elastic constants and Debye temperature of beta-Be are calculated over a wide volume range and compared to those obtained for the low-temperature hexagonal phase (alpha-Be). A significant difference in the anisotropy of the bcc and hcp structures is found. In line with experiments, we predict that the hcp -> bcc phase transition occurs at 240 GPa at 0 K and 239 GPa at ambient temperature. We find that the cubic shear constant C '=(C-11-C-12)/2 rapidly decreases for volumes above similar to 1.05V(0), where V-0 is the zero temperature equilibrium volume for beta-Be. At 1.17V(0), the stability condition C-'> 0 is violated and the bcc phase becomes mechanically unstable. We demonstrate that at 0 K, the softening of beta-Be near its experimental volume of 1.063V(0) is related to an electronic topological transition due to the increased number of occupied s states near the Fermi level compared to that at V-0. This softening turns out to be important for the stability of the bcc phase before melting. The disclosed electronic topological transition is found to be present in other analogous hexagonal metals as well.
Place, publisher, year, edition, pages
2007. Vol. 75, no 3
elastic-constants, free-energy, electronic-properties, ab-initio, pressure, metals, temperature, transitions, approximation, crystals
IdentifiersURN: urn:nbn:se:kth:diva-16360DOI: 10.1103/PhysRevB.75.035132ISI: 000243895400065ScopusID: 2-s2.0-33846708518OAI: oai:DiVA.org:kth-16360DiVA: diva2:334402
QC 201005252010-08-052010-08-05Bibliographically approved