Thermodynamic properties of titanium from ab initio calculations

  Uri Argaman [1]  ,  Eitan Eidelstein [2]  ,  Ohad Levy [2]  ,  Guy Makov [1]  
[1] Materials Engineering Department, Ben-Gurion University of the Negev, Beer Sheva 8410501, Israel
[2] Department of Physics, NRCN, PO Box 9001, IL Beer-Sheva, 84190, Israel

The lattice parameters, lattice stability and phonon dispersion curves of five proposed phases of Ti: αβγδ and ω are investigated within density functional theory (DFT). It is found that the sequence of high pressure phases at zero temperature is α -> ω -> γ -> δ -> β   with the δ and β phases becoming degenerate at high pressure. However, the γ phase may be unstable as is reflected by the existence of imaginary values in the phonon spectra. The results of the DFT calculations are employed to estimate the entropy and free energies of the α and ω phases. It is found that converged phonon calculations lead to an entropy difference which is much smaller than previous estimates, and a much steeper α -> ω phase transition line.

Mater. Res. Express, 2 016505 (2015).