A search for the ground state structure and the phase stability of tantalum pentoxide

Abstract

Tantalum pentoxide (Ta2O5) is a wide-gap semiconductor that presents good catalytic and dielectric properties, conferring to this compound promising prospective use in a variety of technological applications. However, there is a lack of understanding regarding the relations among its crystalline phases, as some of them are not even completely characterized and there is currently no agreement about which models better explain the crystallographic data. Additionally, its phase diagram is unknown. In this work we performed first-principles density functional theory calculations to study the structural properties of the different phases and models of Ta2O5, the equation of state and the zone-centered vibrational frequencies. From our results, we conclude that the phases that are built up from only distorted octahedra instead of combinations with pentagonal and/or hexagonal bipyramids are energetically more favorable and dynamically stable. More importantly, this study establishes that, given the pressure range considered, the B-phase is the most favorable structure and there is no a crystallographic phase transition to another phase at high-pressure. Additionally, for the equilibrium volume of the B-phase and the λ-model, the description of the electronic structure and optical properties were performed using semi-local and hybrid functionals.

Influence of post-deposition annealing on the chemical states of crystalline tantalum pentoxide films

“…It is evident that F1273 exhibits a series of small reflections along the whole pattern that match the reference pattern PDF 025-0922. It is important to underline that so far there has not been a consensus regarding the spatial symmetry of these two phases, and, due to the overlapping of several peaks, one cannot rule out the coexistence of both phases 21,[29][30][31][32][33][34][35][36] .…”

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

“…Despite its wide range of applications, the knowledge of its exact structure is nevertheless still limited. At zero temperature, the structure of ground state Ta 2 O 5 crystal has been under debate for decades . On the other hand, the applied computational researches on Ta 2 O 5 /TaO x have been much rare, compared with HfO 2 /HfO x , though TaO x and HfO x share many properties in common and both are regarded as the most promising candidates for next‐generation memristors.…”

Evidence for structural transition in crystalline tantalum pentoxide films grown by RF magnetron sputtering

“…These patterns can be indexed to either the orthorhombic phase β−Ta 2 O 5 (PDF 00-025-0922 with lattice parameters a = 6.1980Å, b = 40.2900Å, c = 3.8880Å, and α = β = γ = 90 • for the spatial group P 2 1 2 1 2; or PDF 01-089-2843 with lattice parameters a = 6.2000Å, b = 3.6600Å, c = 3.8900 A, and α = β = γ = 90 • for the spatial group Amm2) or the hexagonal phase δ−Ta 2 O 5 (PDF 00-019-1299 with lattice parameters a = b = 3.6240Å, c = 3.8800Å, α = β = 90 • , and γ = 120 • , with presumably spatial group P 6/mmm 23,24 ). As of now, there is still an ongoing debate regarding the specific space group of these two phases 15,16,[25][26][27][28][29] . According to our results, it is clear that as the annealing temperature is raised more peaks in the diffraction patterns show up.…”