Thermodynamic properties of titanium from ab-initio calculations

TL;DR

This study uses ab-initio DFT calculations to analyze the thermodynamic properties and phase stability of five titanium phases, revealing a revised phase sequence and more accurate entropy estimates.

Contribution

It provides new insights into titanium's phase stability and thermodynamics using detailed phonon and free energy calculations within DFT.

Findings

Revised high-pressure phase sequence of Ti.

More accurate entropy difference between alpha and omega phases.

Steeper alpha-omega phase transition line.

Abstract

The lattice parameters, lattice stability and phonon dispersion curves of five proposed phases of Ti: alpha, beta, gamma, delta and omega are investigated within DFT. It is found that the sequence of high pressure phases at zero temperature is alpha, omega, gamma, delta and beta with the delta and beta phases becoming degenerate at high pressure. However, the gamma 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 alpha and omega phases. It is found that converged phonon calculations lead to an entropy difference which is much smaller than previous estimates, and a much steeper alpha-omega phase transition line.