Ab Initio Simulation of Ta2O5: A High Symmetry Ground State Phase with Application to Interface Calculation

• Published in: Annalen der Physik 2019-08, Vol.531 (8), p.n/a
• Main Authors: Yuan, Jun‐Hui, Xue, Kan‐Hao, Chen, Qi, Fonseca, Leonardo R. C., Miao, Xiang‐Shui
• Format: Article
• Language: English
• Subjects: Computer simulation; Contact resistance; Density functional theory; Electronic structure; Ground state; High temperature; Niobium oxides; self‐energy correction; space group; Symmetry; Tantalum; Tantalum oxides; tantalum pentoxide; tetragonal Ta2O5; γ‐phase Ta2O5
• ISSN: 0003-3804; 1521-3889
• DOI: 10.1002/andp.201800524

It is reported that the recently predicted triclinic γ‐phase ground state Ta2O5 by Yang and Kawazoe can be assigned a much more symmetric I41/amd space group, and is isomorphic to P‐Nb2O5. Interestingly, the well‐known high temperature α‐phase Ta2O5 also has the I41/amd symmetry, but is unstable at zero temperature according to our phonon dispersion calculation. A thorough energy comparison of the βAL, δ, λ, Β, LSR, βR, Pm, Cmmm, γ, and α 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 γ‐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 γ‐Ta2O5, using GGA‐1/2 has been explicitly shown. A tetragonal I41/amd space group is identified for the recently predicted γ‐phase ground state Ta2O5 by Yang and Kawazoe. The tetragonal γ‐Ta2O5 is isomorphic to the well‐known P‐Nb2O5, and is related to the orthorhombic Cmmm‐Ta2O5 model by twisting‐mirroring operations. Self‐energy corrected density functional calculation reveals a 4.24 eV indirect band gap for γ‐Ta2O5.