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

TL;DR

This study identifies a high-symmetry tetragonal phase of Ta2O5 as its ground state using ab initio simulations, demonstrating its stability, electronic properties, and application to interface modeling with metals.

Contribution

The paper proposes a new high-symmetry tetragonal ground state for Ta2O5 and validates its stability and electronic properties using advanced ab initio methods, facilitating device simulations.

Findings

The $ ext{I4}_1/amd$ phase is the ground state of Ta2O5 at zero temperature.

The $ ext{eta}$-phase is dynamically stable and has a 4.24 eV indirect band gap.

The high-symmetry phase enables efficient ab initio device modeling.

Abstract

We suggest a tetragonal $I4_1/amd$ phase ($\eta$-phase) as the ground state of $\mathrm{Ta_2O_5}$ at zero temperature, which is a high symmetry version of the triclinic $\gamma$-phase $\mathrm{Ta_2O_5}$ predicted by Yang and Kawazoe. Our calculation shows that $\gamma$-phase $\mathrm{Ta_2O_5}$ will automatically be transformed into the $\eta$-phase during structural relaxation. Phonon dispersion confirms that the $\eta$-phase is dynamically stable, while the high temperature $\alpha$-phase $\mathrm{Ta_2O_5}$, which also has the $I4_1/amd$ symmetry, is unstable at zero temperature. A thorough energy comparison of the $\beta_{AL}$, $\delta$, $\lambda$, $\mathrm{B}$, $\mathrm{L_{SR}}$, $\beta_R$, $Pm$, $Cmmm$, $\gamma$, $\eta$ and $\alpha$ 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 $\eta$-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 $\eta$-$\mathrm{Ta_2O_5}$, using GGA-1/2.