Ab Initio Simulation Of Ta2o5: A High Symmetry Ground State Phase With Application To Interface Calculation

It is reported that the recently predicted triclinic gamma-phase ground state Ta2O5 by Yang and Kawazoe can be assigned a much more symmetric I4(1)/amd space group, and is isomorphic to P-Nb2O5. Interestingly, the well-known high temperature alpha-phase Ta2O5 also has the I4(1)/amd symmetry, but is unstable at zero temperature according to our phonon dispersion calculation. A thorough energy comparison of the beta(AL), delta, lambda, Beta, L-SR, beta(R), Pm, Cmmm, gamma, and alpha phases of Ta2O5 is carried out using density functional theory under the generalized gradient approximation (GGA). The GGA-1/2 method is applied in calculating the electronic structure of various phases, where the tetragonal gamma-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 facilitates the ab initio simulation of Ta2O5-based devices. As an example, the Ohmic contact nature between metal Ta and Ta2O5 by calculating an interface model of b.c.c. Ta and tetragonal gamma-Ta2O5, using GGA-1/2 has been explicitly shown.