Ab initio simulation of $\mathrm{Ta_2O_5}$: A high symmetry ground state phase with application to interface calculation

Abstract

We suggest a tetragonal $I4_1/amd$ phase ($η$-phase) as the ground state of $\mathrm{Ta_2O_5}$ at zero temperature, which is a high symmetry version of the triclinic $γ$-phase $\mathrm{Ta_2O_5}$ predicted by Yang and Kawazoe. Our calculation shows that $γ$-phase $\mathrm{Ta_2O_5}$ will automatically be transformed into the $η$-phase during structural relaxation. Phonon dispersion confirms that the $η$-phase is dynamically stable, while the high temperature $α$-phase $\mathrm{Ta_2O_5}$, which also has the $I4_1/amd$ symmetry, is unstable at zero temperature. A thorough energy comparison of the $β_{AL}$, $δ$, $λ$, $\mathrm{B}$, $\mathrm{L_{SR}}$, $β_R$, $Pm$, $Cmmm$, $γ$, $η$ and $α$ phases of $\mathrm{Ta_2O_5}$ is carried out. The GGA-1/2 method is applied in calculating the electronic structure of various phases, where the $η$-phase demonstrates a 4.24 eV indirect band gap, close to experimental value. The high symmetry tetragonal phase together with computationally efficient GGA-1/2 method greatly facilitate the $ab\ initio$ simulation of $\mathrm{Ta_2O_5}$-based devices. As an example, we have explicitly shown the Ohmic contact nature between metal Ta and $\mathrm{Ta_2O_5}$ by calculating an interface model of $b.c.c.$ Ta and $η$-$\mathrm{Ta_2O_5}$, using GGA-1/2.