Tuning the electronic band structure of microporous titanates with the hollandite structure

Moetakef, Pouya; Wang, Limin; Maughan, Annalise E.; Gaskell, Karen J.; Larson, Amber M.; Hodges, Brenna C.; Rodriguez, Efrain E.

doi:10.1039/c5ta05288b

Cited by 9 publications

(10 citation statements)

References 52 publications

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“…type materials are considered as a component in the Synroc ensemble to immobilize radioactive Cs and Ba produced in a nuclear reactor. − Besides, hollandite type materials are also of interest for various physical and chemical properties. Spin transitions and Mott–Peierls transitions have been reported in several transition metal containing hollandites. − Hollandite type materials with smaller cations exhibit fast cation conduction due to the free motion of ions in the channels. , …”

Section: Introductionmentioning

confidence: 99%

Pressure and Temperature Dependent Structural Studies on Hollandite Type Ferrotitanate and Crystal Structure of a High Pressure Phase

et al. 2018

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The structural stability and phase transition behavior of tetragonal (I4/m) hollandite type KFeTiO have been investigated by in situ high pressure X-ray diffraction using synchrotron radiation and a diamond anvil cell as well as by variable temperature powder neutron and X-ray diffraction. The tetragonal phase is found to be stable in a wider range of temperatures, while it reversibly transforms to a monoclinic (I2/m) structure at a moderate pressure, viz. 3.6 GPa. The pressure induced phase transition occurs with only a marginal change in structural arrangements. The unit cell parameters of ambient (t) and high pressure (m) phases can be related as a ∼ a, b ∼ c, and c ∼ b. The pressure evolution of the unit cell parameters indicates anisotropic compression with β = β ≥ β in the tetragonal phase and becomes more anisotropic with β ≪ β < β in the monoclinic phase. The pressure-volume equations of state of both phases have been obtained by second order Birch-Murnaghan equations of state, and the bulk moduli are 122 and 127 GPa for tetragonal and monoclinic phases, respectively. The temperature dependent unit cell parameters show nearly isotropic expansion, with marginally higher expansion along the c-axis compared to the a- and b-axes. The tetragonal to monoclinic phase transition occurs with a reduction of unit cell volume of about 1.1% while the reduction of unit cell volume up to 6 K is only about 0.6%. The fitting of temperature dependent unit cell volume by using the Einstein model of phonons indicates the Einstein temperature is about 266(18) K.

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Section: Introductionmentioning

confidence: 99%

Pressure and Temperature Dependent Structural Studies on Hollandite Type Ferrotitanate and Crystal Structure of a High Pressure Phase

et al. 2018

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“…The addition of Co 2+ to the framework disrupts the helical order giving rise to a ferrimagnetically ordered state with a greatly increased transition temperature, TC, of 180 K. 7 The same group also investigated the magnetic behaviour of Bi1.7V8O16 and Sc to Ni doped (denoted by M) KxTi8-yMyO16 materials. [12][13][14] All KxTi8-yMyO16 materials exhibited curie paramagnetism consistent with the limited amounts of magnetic species incorporated into these materials. 13 In contrast, whilst the Bi1.7V8O16 material exhibits no long range magnetic order, as observed by powder neutron diffraction, magnetotransport measurements suggest a dimerization of the mixed spin-cations.…”

Section: Introductionmentioning

confidence: 62%

Spin-glass behavior in KxRu4−yNiyO
Stimpson
¹
,
Powell
²
,
Stenning
³

et al. 2018
Phys. Rev. B
9
0
1
0
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We report the synthesis and comprehensive AC and DC susceptibility measurements of KxRu4-yNiyO8 hollandite. The value of the relative frequency shift, δTf, has been determined as 0.025 which is within the range expected for spin-glass systems (0.005 -0.06). Additionally, the characteristic flipping time of a single spin flip, τ0, and the dynamical critical exponent, -zv were determined to have values 5.82 x 10 -8 s and 6.1(3) respectively from the Power Law. Whilst the value of τ0 is comparatively very large, -zv is consistent with what is expected for spin glass systems. Field cooled hysteresis behaviour demonstrates a small increase in the remnant magnetisation (at 2 K) on increasing the strength of the cooling field suggesting that the degree of short-range correlations increases consistent with the formation of larger spin clusters. Thermoremnant magnetisation data indicates an exponential-like decay of the magnetisation as a function of time with the remnant magnetisation remaining nonzero. However, it is clear from these data that multiple components contribute to the decay behaviour. Collectively, these data confirm spin-glass character for K0.73(3)Ni1.9(5)Ru2.1(5)O8 and clearly demonstrate that the magnetic behaviour of this material is far from simplistic.

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“…23,24 Theoretical studies of TiO 2 focused, for example, on band position tuning by Se doping (ΔVBM DFT = 1.8 eV and ΔCBM DFT = ∼0.4 eV), 25 Ga doping (ΔVBM DFT = ∼0.6 eV and ΔCBM DFT = ∼0.9 eV), 26 or titanates with a hollandite structural motif (ΔVBM DFT = 1.1 eV and ΔCBM DFT = ∼0 eV) where the choice of cations also introduces shallow and deeper gap states. 27 Direct experimental verification of band edge positions for these systems is generally missing, limiting evaluation of whether broad band edge energy tunability can be realized and limiting its direct correlation with PEC performance.…”

Section: Introductionmentioning

confidence: 99%

Band Edge Energy Tuning through Electronic Character Hybridization in Ternary Metal Vanadates

et al. 2021

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In the search for photoanode materials with band gaps suitable for utilization in solar fuel generation, approximately 1.2–2.8 eV, theory-guided experiments have identified a variety of materials that meet the band gap requirements and exhibit operational stability in harsh photoelectrochemical environments. In particular, M-V-O compounds (M is a transition metal or main group element) with VO4 structural motifs were predicted to show a remarkably wide range of band energetics (>3 eV variation in the energy of valence band maximum) and characteristics, depending on the M and crystal structure, which is beyond the extent of electronic structured tuning observed in previously studied families of metal oxide photoanodes. While this finding guided experimental discovery of new photoanode materials, explicit experimental verification of the theoretical prediction of the tunable electronic structure of these materials has been lacking to date. In this study, we use X-ray photoelectron spectroscopy and Kelvin probe microscopy to experimentally investigate the electronic structure of M-V-O photoanodes, enabling comparison to theory on a common absolute energy scale. The results confirm the prediction that band edge energies of ternary vanadates vary significantly with metal cations. The valence band variation of approximately 1 eV observed here is larger than that reported in any analogous class of metal oxide semiconductors and demonstrates the promise of tuning the metal oxide electronic structure to enable efficient photoelectrocatalysis of the oxygen evolution reaction and beyond. Because midgap states can hamper realization of the high photovoltage sought by band edge tuning, we analyze the electronic contributions of oxygen vacancies for the representative photoanode V4Cr2O13 to guide future research on the development of high-efficiency metal oxide photoanodes for solar fuel technology.

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Tuning the electronic band structure of microporous titanates with the hollandite structure

Abstract: We present the electronic band structures of microporous titanates with the hollandite-type structure.

Cited by 9 publications

References 52 publications

Pressure and Temperature Dependent Structural Studies on Hollandite Type Ferrotitanate and Crystal Structure of a High Pressure Phase

Pressure and Temperature Dependent Structural Studies on Hollandite Type Ferrotitanate and Crystal Structure of a High Pressure Phase

Spin-glass behavior in KxRu4−yNiyO
Stimpson
¹
,
Powell
²
,
Stenning
³

et al. 2018
Phys. Rev. B
9
0
1
0
View full text Add to dashboard Cite

Band Edge Energy Tuning through Electronic Character Hybridization in Ternary Metal Vanadates

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Tuning the electronic band structure of microporous titanates with the hollandite structure

Abstract: We present the electronic band structures of microporous titanates with the hollandite-type structure.

Cited by 9 publications

References 52 publications

Pressure and Temperature Dependent Structural Studies on Hollandite Type Ferrotitanate and Crystal Structure of a High Pressure Phase

Pressure and Temperature Dependent Structural Studies on Hollandite Type Ferrotitanate and Crystal Structure of a High Pressure Phase

Spin-glass behavior in KxRu4−yNiyOStimpson1, Powell2, Stenning3 et al. 2018Phys. Rev. B9010View full textAdd to dashboardCite

Band Edge Energy Tuning through Electronic Character Hybridization in Ternary Metal Vanadates

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Spin-glass behavior in KxRu4−yNiyO
Stimpson
¹
,
Powell
²
,
Stenning
³

et al. 2018
Phys. Rev. B
9
0
1
0
View full text Add to dashboard Cite