Combined experimental and theoretical assessments of the lattice dynamics and optoelectronics of TaON and Ta3N5

Nurlaela, Ela; Harb, Moussab; Gobbo, Silvano Del; Vashishta, Manish; Takanabe, Kazuhiro

doi:10.1016/j.jssc.2015.06.029

Cited by 93 publications

(95 citation statements)

References 62 publications

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“…34,35 we computed the infrared and Raman frequencies of Ta 3 N 5 at the Brillouin Zone center (see Table SI) using PBE, and we found excellent agreement with the theoretical and experimental data of Ref. 36. We also found that frequencies larger than 300 cm −1 are dominated by N displacements.…”

Section: Resultssupporting

confidence: 78%

Charge transport properties of bulkTa3N5from first principles

Morbec

Galli

2016

Phys. Rev. B

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Tantalum nitride is considered a promising material for photoelectrochemical water splitting, however its charge transport properties remain poorly understood. We investigated polaronic and band transport in Ta 3 N 5 using first-principles calculations. We first studied the formation of small polarons using density-functional theory (DFT) including DFT+U and hybrid functionals. We found that electron small polarons may occur but hole polarons are not energetically favorable.The estimated polaronic mobility for electrons is at least three orders of magnitude smaller than that measured in Ta 3 N 5 films, suggesting that the main transport mechanism for both electrons and holes is band-like. Since band transport is strongly affected by the carrier effective masses, and Ta 3 N 5 in known to have large electron and hole effective masses, we also investigated whether substitutional impurities or strain may help lower the effective masses. We found significant reduction in both electron and hole effective masses (up to 17% for electron and 39% for hole) under applied strain, which may lead to substantial improvement (up to 30% for electron and 15% for hole) in the carrier mobilities.

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Section: Resultssupporting

confidence: 78%

Charge transport properties of bulkTa3N5from first principles

Morbec

Galli

2016

Phys. Rev. B

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“…The frequencies of 140.7, 401.8, 523.3, and 898.1 cm −1 can be assigned to Ag modes and 125, 178.6, 238.8, 265.6, 492.9, 599.1, and 746.6 cm −1 correspond to Bg modes. [15] All peaks are consistent with the theoretical calculations with an error value less than 5 cm −1 , indicating that these nanomeshes are single-phase Ta 3 N 5 . X-ray photoelectron spectroscopy (XPS) was used to examine the chemical states of Ta and N in the Ta 3 N 5 nanomeshes (Figure 3c,d).…”

supporting

confidence: 84%

“…A laser of 337 nm was used as excitation source and the lifetime of photons at the wavelength of 586 nm (2.116 eV) was monitored due to the highest emission intensity of Ta 3 N 5 under this wavelength. [15] As shown in Figure 5c, the fluorescent intensities decay exponentially for both samples. Noticeably, the nanomesh shows slow decay kinetics compared to the bulk.…”

mentioning

confidence: 71%

Single‐Crystalline Nanomesh Tantalum Nitride Photocatalyst with Improved Hydrogen‐Evolving Performance

Xiao

Luo

Lyu

et al. 2017

Advanced Energy Materials

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alignment and excellent interfacial contact. [8] By contrast, carefully engineering the nanostructure of Ta 3 N 5 with good crystallinity to shorten the migration length of charge carriers and provide more reactive sites may open up new opportunities for efficient water splitting.Over the past decade, enlightened by the breakthrough of graphene, [9] 2D nanomaterials have attracted increasing research-attention in the field of energy storage and conversion because they possess advantages of large specific surface area, high ratio of surface atoms, and facile charge transport behaviour. [10] However, the amount of catalytic active sites in 2D nanosheets is still confined due to the limited boundaries and exposed edges. It has been demonstrated that constructing 2D nanosheets with abundant and well-distributed pores, or namely, nanomeshes, can solve this problem and greatly improve the catalytic performance. [11] Unfortunately, the construction of ultrathin nanomeshes is mainly limited to the materials with layered structure, such as graphene, boron nitride, and layered double hydroxides. [11a,12] The fabrication of ultrathin nanomeshes for the nonlayered and transition metalbased materials such as Ta 3 N 5 with potentially high catalytic activity is of great challenge.Herein, we innovatively synthesize ultrathin single-crystalline Ta 3 N 5 nanomeshes using graphene oxide (GO) nanosheets as a 2D template. Remarkably, the obtained 2D Ta 3 N 5 nanomeshes with a lateral size of several micrometres and an average thickness of ≈2 nm show large aspect ratios, high specific surface area (284.6 m 2 g −1 ), and excellent crystallinity. The interplane pores provide numerous new active edges which can greatly speed up mass transfer and charge migration. Furthermore, the high crystallinity is also beneficial for charge separation. By loading 1 wt% of Pt as cocatalysts, the Ta 3 N 5 nanomeshes exhibit over tenfold improvement of solar hydrogen production when compared to its bulk counterpart. [1b] This work provides a novel strategy for designing 2D ultrathin nanomesh structures for nonlayered materials with improved photocatalytic activity.As shown in Figure 1, Ta 3 N 5 nanomeshes were synthesized via a bottom-up process using GO as a template. First, a thin layer of amorphous Ta-aquo-complex was uniformly deposited on the GO sheets by a homogeneous hydrolysis process of TaCl 5 , yielding GO/Ta-aquo-complex composite nanosheets. Then, the GO template was removed using a calcination procedure to obtain 2D-TaO x nanosheets. Finally, the Tantalum nitride (Ta 3 N 5 ) with a suitable bandgap (≈2 eV) is regarded as one of the most promising photocatalysts for efficient solar energy harvesting and conversion. However, Ta 3 N 5 suffers from low hydrogen production activity due to the low carrier mobility and fast carrier recombination. Thus, the design of Ta ) and excellent crystallinity by an innovative bottom-up graphene oxide templated strategy. The resulting Ta 3 N 5 nanomeshes demonstrate drastically improved electron trans...

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“…Because there is only limited literature describing the Raman modes of Ta 3 N 5 , a detailed assignment for Ta 3 N 5 Raman modes based on theoretical calculations was previously performed in our recent study. 21,56 To summarize, the theory predicted for the orthorhombic allotrope (Cmcm) of Ta 3 N 5 a total of 24 Raman-active modes (8A g +16B g ). X-ray absorption spectroscopy (XAS) with sensitive fluorescence detection was used to unveil the local environment of the cobalt.…”

Section: Chemistry Of Materialsmentioning

confidence: 98%

Establishing Efficient Cobalt-Based Catalytic Sites for Oxygen Evolution on a Ta₃N₅ Photocatalyst

et al. 2015

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ABSTRACT:In a photocatalytic suspension system with a powder semiconductor, the interface between the photocatalyst semiconductor and catalyst should be constructed to minimize resistance for charge transfer of excited carriers. This study demonstrates an in-depth understanding of pretreatment effects on the photocatalytic O 2 evolution reaction (OER) activity of visible-lightresponsive Ta 3 N 5 decorated with CoO x nanoparticles. The CoO x /Ta 3 N 5 sample was synthesized by impregnation followed by sequential heat treatments under NH 3 flow and air flow at various temperatures. Various characterization techniques, including X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), scanning transmission electron microscopy (STEM), and X-ray photoelectron spectroscopy (XPS), were used to clarify the state and role of cobalt. No improvement in photocatalytic activity for OER over the bare Ta 3 N 5 was observed for the as-impregnated CoO x /Ta 3 N 5 , likely because of insufficient contact between CoO x and Ta 3 N 5 . When the sample was treated in NH 3 at high temperature, a substantial improvement in the photocatalytic activity was observed. After NH 3 treatment at 700 °C, the Co 0 -CoO x core-shell agglomerated cobalt structure was identified by XAS and STEM. No metallic cobalt species was evident after the photocatalytic OER, indicating that the metallic cobalt itself is not essential for the reaction. Accordingly, mild oxidation (200 °C) of the NH 3 -treated CoO x /Ta 3 N 5 sample enhanced photocatalytic OER activity. Oxidation at higher temperatures drastically eliminated the photocatalytic activity, most likely because of unfavorable Ta 3 N 5 oxidation. These results suggest that the intimate contact between cobalt species and Ta 3 N 5 facilitated at high temperature is beneficial to enhancing hole transport and that the cobalt oxide provides electrocatalytic sites for OER. IntroductionWater splitting using powder photocatalyst systems has attracted significant interest for the production of renewable hydrogen generation using abundant solar energy because of its simplicity, scalability, and low capital cost.1,2 To effectively convert solar energy, substantial utilization of photon energy in the visible-light range is essential. Using the AM 1.5G standard spectrum 3 , a photocatalyst with absorption from UV to 600 nm with a quantum efficiency of 30% accounts for ~5% solar to hydrogen efficiency, making the technology commercially feasible.1,4 Among the photocatalysts investigated to date, tantalum(V) nitride (Ta 3 N 5 ) has emerged as one of the most promising candidates and has been extensively investigated for more than a decade. [4][5][6][7][8][9][10][11][12][13][14][15] Ta 3 N 5 has a visible-light response (approximately 600 nm, ~2.1-eV band gap) and is capable of producing hydrogen or oxygen in the presence of appropriate sacrificial reagents and surface modifications under visible-light irradiation. 1,[5][6][7][8][9][10][11][12][13][14][15][16] Our recent work on Ta 3 N 5 thin films for the photo...

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Combined experimental and theoretical assessments of the lattice dynamics and optoelectronics of TaON and Ta3N5

Cited by 93 publications

References 62 publications

Charge transport properties of bulkTa3N5from first principles

Charge transport properties of bulkTa3N5from first principles

Single‐Crystalline Nanomesh Tantalum Nitride Photocatalyst with Improved Hydrogen‐Evolving Performance

Establishing Efficient Cobalt-Based Catalytic Sites for Oxygen Evolution on a Ta₃N₅ Photocatalyst

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Combined experimental and theoretical assessments of the lattice dynamics and optoelectronics of TaON and Ta3N5

Cited by 93 publications

References 62 publications

Charge transport properties of bulkTa3N5from first principles

Charge transport properties of bulkTa3N5from first principles

Single‐Crystalline Nanomesh Tantalum Nitride Photocatalyst with Improved Hydrogen‐Evolving Performance

Establishing Efficient Cobalt-Based Catalytic Sites for Oxygen Evolution on a Ta3N5 Photocatalyst

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Establishing Efficient Cobalt-Based Catalytic Sites for Oxygen Evolution on a Ta₃N₅ Photocatalyst