Tailoring of the Solid State Properties of Al–Nb Mixed Oxides: A Photoelectrochemical Study

Santamaria, Monica; Franco, Francesco Di; Quarto, F. Di; Skeldon, P.; Thompson, G.E.

doi:10.1021/jp312008m

Cited by 29 publications

(55 citation statements)

References 37 publications

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“…The determined bowing parameter is lower than the one reported for anodic Al-Nb mixed oxides, i.e., 4.3 eV. 4 Typically, a small value of the bowing parameter, and thus a small deviation from the linearity of the band gap of alloys, can indicate a good miscibility of the alloys, such as b ¼ 0.1, as estimated from polycrystalline CZGTS (Se) alloys. 20 A larger value of the bowing parameter, such as the one determined here and also reported for Al-Nb mixed oxides, indicates that the randomness in the alloys strongly influences the energy gap of the alloys.…”

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confidence: 69%

“…Several studies were dedicated to understanding the electronic properties and changes in the band gap of amorphous anodic Al 2 O 3 upon alloying. [3][4][5] Theoretical studies based on density functional theory have shown that transition metal atoms, such as Zr atoms present in Al sites, introduce localized d-electron states below the conduction band (CB) of Al 2 O 3 . 6 Experimental determination of the band gap energy of Zr-alloyed Al 2 O 3 is not readily available because ultraviolet and visible measurements are limited to energies below 6 eV due to the absorption of air.…”

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confidence: 99%

“…A lower optical band gap of amorphous oxide compared to its crystalline counterpart can be associated with the different band structure resulting from a broad distribution of bond angles and distances. 4,5 In fact, it was shown that the band gap of Al 2 O 3 can be increased by $1 eV from an amorphous to a crystalline structure by annealing induced crystallization. 16 Filatova et al 17 6 The electronic structure of Al 2 O 3 is well understood.…”

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confidence: 99%

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Band gap tuning of amorphous Al oxides by Zr alloying

Canulescu

Jones

Borca

et al. 2016

Applied Physics Letters

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The optical band gap and electronic structure of amorphous Al-Zr mixed oxides with Zr content ranging from 4.8 to 21.9% were determined using vacuum ultraviolet and X-ray absorption spectroscopy. The light scattering by the nano-porous structure of alumina at low wavelengths was estimated based on the Mie scattering theory. The dependence of the optical band gap of the Al-Zr mixed oxides on the Zr content deviates from linearity and decreases from 7.3 eV for pure anodized Al2O3 to 6.45 eV for Al-Zr mixed oxides with a Zr content of 21.9%. With increasing Zr content, the conduction band minimum changes non-linearly as well. Fitting of the energy band gap values resulted in a bowing parameter of ∼2 eV. The band gap bowing of the mixed oxides is assigned to the presence of the Zr d-electron states localized below the conduction band minimum of anodized Al2O3.

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confidence: 69%

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confidence: 99%

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confidence: 99%

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Band gap tuning of amorphous Al oxides by Zr alloying

Canulescu

Jones

Borca

et al. 2016

Applied Physics Letters

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“…This procedure allowed correlation of the bandgap values measured by PCS with the mixed oxide composition, as confirmed with several mixed oxides of known composition. [3][4][5][6]8,9 In this work, we will discuss the limits of validity of Eqs. 1a and 1b for binary and ternary oxides spanning a large range of bandgap values (from ∼1 eV to ∼9 eV) by discussing data reported in the literature pertaining to ternary mixed oxides prepared by different techniques and including anodic passive films grown on metallic alloys.…”

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confidence: 99%

Critical Review—Photocurrent Spectroscopy in Corrosion and Passivity Studies: A Critical Assessment of the Use of Band Gap Value to Estimate the Oxide Film Composition

Quarto

Zaffora

Franco

et al. 2017

J. Electrochem. Soc.

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A critical assessment of the Photocurrent Spectroscopy (PCS) Technique for the semi-quantitative characterization of passive film and corrosion layers composition is carried out. We take into account more than three decades of PCS usage as "in-situ" analytical technique and related results as well as the criticism of the underlying semi-empirical correlation relating the measured optical bandgap (E g ) to the passive film composition. The discrepancies between the experimental data, gathered by PCS measurements, and E g estimates originating from recently developed Density Functional Theory based modeling of solid state properties are stressed with particular emphasis on the case of anodic passive film grown on technologically important alloys (Fe-Cr and stainless steels). The extension of this correlation to mixed oxides and its use for relating the oxide composition to the bandgap values is critically reviewed by comparing the predicted E g of mixed oxides with the experimental values. Suggestions on how to account for different bandgap values of oxide polymorphs and how to correlate the E g values to the composition of mixed s,p-d-metal oxides are presented and discussed on the basis of experimental results reported in the literature. On the basis of this assessment, the ability of PCS in providing quantitative information on the composition of passive film and corrosion layer is generally confirmed. Fujimoto (fujimoto@mat.eng.osaka-u.ac.jp) and HeeJin Jang (heejin@chosun.ac.kr). . This paper is a Critical Review in Electrochemical and Solid State Science and Technology (CRES 3 T). This article was reviewed by ShinjiPhotocurrent Spectroscopy (PCS) is currently employed for the characterization of solid-state properties of semiconducting and insulating materials, since the knowledge of their bandgap is a prerequisite to any possible application in different fields such as solar energy conversion (photoelectrochemical and photovoltaic solar cells, photocatalysis) and microelectronics (high-k, high band-gap materials). 1,2In the last 20-30 years an increasing number of electrochemists working in the field of corrosion have been attracted by this technique owing to its versatility and ability to scrutinize "in-situ" corrosion layers and passive films having semiconducting or insulating behavior. In previous as well as in very recent works 3-7 we have shown that PCS is able to provide detailed information on characteristic energy levels of passive film/electrolyte junctions (flatband potential: U FB ; internal photoemission threshold: E th ; bandgap value: E g ). Such information is necessary for a deeper understanding of the possible mechanisms of charge transfer (electrons and ions) at the metal/corrosion layer/electrolyte interface. Further advantages stem from the fact that the PCS technique does not require particular surface finishing control, it can be used both on large areas as well as in microscopic regions of the electrode, and can reach high sensitivity by using a lock-in amplifier coupled to a mec...

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“…Semi-empirical correlation between the electronegativity and band gap of oxides has been used recently to estimate the band gap of mixed metal oxides. 4,5 While anodic Al oxide layers are widely used, few studies on band gap structure of anodic oxide films have been reported. 5 In this Letter, we study the effect of Ti alloying on the electronic structure and band gap states of amorphous anodic aluminum oxide.…”

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Band gap structure modification of amorphous anodic Al oxide film by Ti-alloying

Canulescu

Rechendorff

Borca

et al. 2014

Applied Physics Letters

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The band structure of pure and Ti-alloyed anodic aluminum oxide has been examined as a function of Ti concentration varying from 2 to 20 at. %. The band gap energy of Ti-alloyed anodic Al oxide decreases with increasing Ti concentration. X-ray absorption spectroscopy reveals that Ti atoms are not located in a TiO2 unit in the oxide layer, but rather in a mixed Ti-Al oxide layer. The optical band gap energy of the anodic oxide layers was determined by vacuum ultraviolet spectroscopy in the energy range from 4.1 to 9.2 eV (300–135 nm). The results indicate that amorphous anodic Al2O3 has a direct band gap of 7.3 eV, which is about ∼1.4 eV lower than its crystalline counterpart (single-crystal Al2O3). Upon Ti-alloying, extra bands appear within the band gap of amorphous Al2O3, mainly caused by Ti 3d orbitals localized at the Ti site.

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Tailoring of the Solid State Properties of Al–Nb Mixed Oxides: A Photoelectrochemical Study

Cited by 29 publications

References 37 publications

Band gap tuning of amorphous Al oxides by Zr alloying

Band gap tuning of amorphous Al oxides by Zr alloying

Critical Review—Photocurrent Spectroscopy in Corrosion and Passivity Studies: A Critical Assessment of the Use of Band Gap Value to Estimate the Oxide Film Composition

Band gap structure modification of amorphous anodic Al oxide film by Ti-alloying

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