Dopant Clusterization and Oxygen Coordination in Ta-Doped Bismuth Oxide: A Structural and Computational Insight into the Mechanism of Anion Conduction

Abstract

Bi2O3 in its fluorite-like form can be obtained either at 730-824 °C, showing the highest oxide-ion conduction known so far, or by doping. We present a comprehensive appraisal of the local atomic structure of Ta-doped Bi2O3 investigating by X-ray absorption spectroscopy the aggregation motifs of Ta5+ and the interaction between dopants and oxygen vacancies. Using periodic density functional theory simulations, we show that the connection of Ta4O18 aggregates is energetically favorable. We find that the local coordination of Bi3+ and its electronic structure, as seen from the calculated density of states (DOS), are invariably determined by the Bi 6s2 lone pair in both doped and undoped Bi2O3. This does not depend on the long-range symmetry that is revealed by X-ray diffraction studies. From the similarity of the DOS of α-Bi2O3 and Ta-doped bismuth oxide, it is inferred that the force governing the local coordination of Bi is essentially the same in all forms of Bi2O3. As the local Bi environment, determined by X-ray absorption spectroscopy, is also found to be very similar in all investigated samples, regardless of the dopant concentration, the local mechanism of oxide ion diffusion is arguably similar in doped and undoped bismuth oxide

Rational Design of a Commensurate (3 + 3)-D Modulated Structure within the Fast-Ion Conducting Stabilized δ-Bi2O3 Series

“…Type II Bi 1– x Ta x 5+ O 1.5+ x was shown to crystallize in space group Fm 3̅ m (α,α,α) q 00­(α,α̅,α̅) q 00­(α̅,α,α̅)­000 with reported incommensurate modulation parameters in a similar range as observed in the niobium system (ε = 0.388 for x = 0.25; ε = 0.385 for x = 0.20). XAS measurements confirmed exclusively octahedral coordination environments around the Ta dopants except at very low Ta concentrations . At these lower Ta concentrations, a larger pseudocubic Type I phase was reported between 0.05 < x < 0.07 ( a ∼ 5.52 Å), and a mixture of Type I and Type II phases were found at intermediate compositions (0.07 < x < 0.20).…”

“…XAS measurements confirmed exclusively octahedral coordination environments around the Ta dopants except at very low Ta concentrations. 26 At these lower Ta concentrations, a larger pseudocubic Type I phase was reported between 0.05 < x < 0.07 (a ∼ 5.52 Å), and a mixture of Type I and Type II phases were found at intermediate compositions (0.07 < x < 0.20).…”

Defect interaction and local structural distortions in Mg-doped LaGaO3: A combined experimental and theoretical study

“…[21][22][23] More precisely, atomistic techniques [17][18][19] have been extensively used to examine dopant-vacancy association, revealing that oxygen vacancies tend to be trapped by Mg 2+ defects (E binding (Mg j GaV0 •• ) = 1.77 eV). A recent theoretical DFT investigation using the PBE functional combined with experimental NMR measurements on 71 Ga, 25 Mg and 17 O nuclei demonstrated that in Mg-doped lanthanum gallate, vacancies tend to be localized on Ga sites while Mg coordination is found to be mainly octahedral. 21 Moreover, the chemical shifts of the 17 O nuclei, which are found to be sensitive enough to distinguish between equatorial (O eq ) and axial (O ax ) oxygen atoms in GaO 5 Vo local environments, revealed a heavily distorted square pyramidal geometry, with a shortening of 0.08-0.09 Å of the Ga-O axial bond length.…”

“…Our previous works showed how combining DFT based on hybrid functionals with X-ray Absorption Spectroscopy (XAS) can lead to helpful complementary information about doped solid state electrolytes. 25,26 Indeed, X-ray absorption spectroscopy can give useful short-range information concerning bond distances, coordination numbers, and static disorder of solid-state materials. On the other hand, since local distortions around vacancy sites induced by Mg doping could remain "hidden" in the EXAFS spectra of doped lanthanum gallate due to the larger population of fully coordinated Ga and Mg atoms, a more complete understanding of the local structure and the electronic features around Vo conducting sites requires modelling such systems with adequate theoretical tools.…”

Photocatalytic Activity of Bi2O3 Enhanced by the Addition of Ce3+/Ce4+ Synthesized by Ethylene Glycol‐assisted Solvothermal Method

“…Recently, many investigations have been published on extending the stability of the cubic δphased Bi 2 O 3 to room temperature via cations doping. [19,20] Several works on the stability of the δ-Bi 2 O 3 by introduce of high-valence cations, such as Re 7 + , Mo 6 + , Ta 5 + , Nb 5 + and V 5 + , [21][22][23][24][25] have been well documented for photocatalysis purposes. However, their photocatalytic activities are not as high as expected, which are mainly attributed to their low potentials of conduction band (CB).…”