Hydride ions in oxide hosts hidden by hydroxide ions

Hayashi, Katsuro; Sushko, Peter V.; Hashimoto, Yoshihiro; Shluger, Alexander L.; Hosono, Hideo

doi:10.1038/ncomms4515

Cited by 113 publications

(125 citation statements)

References 51 publications

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“…The observed 1 H NMR resonance at 9 ppm is in a range that is consistent with H int and suggests that their most likely positions are in locations with OH•••O distances of 275-280 pm. 33 From these results, it can be concluded that hydrogen incorporates into BiVO 4 as both H O and H int upon H 2 annealing. Importantly, our results also indicate that hydrogen is present at lower concentrations in as-grown material in the form of H O .…”

Section: Hydrogen Incorporation In Bivomentioning

confidence: 84%

“…Hyashi et al examined the 1 H chemical shifts arising from hydride (H -) and hydroxide (OH -) incorporated in a number of host metal oxide materials. 33 The authors discovered a linear relationship of the chemical shift with the metal-hydrogen bond distance in the hydride bond, as well as with the distance between neighbouring oxygen atoms and the hydroxide associated with interstitial hydrogen (OH•••O). Herein, density functional theory (DFT) was used to understand the structure of both hydrogen defect types and aid the assignment of the solid-state NMR resonances.…”

Section: Hydrogen Incorporation In Bivomentioning

confidence: 99%

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Role of Hydrogen in Defining the n-Type Character of BiVO₄ Photoanodes

Cooper¹,

Scott²,

et al. 2016

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The roles of hydrogen impurity and oxygen vacancy defects on defining the conductivity, and hence photoelectrochemical (PEC) performance characteristics, of monoclinic scheelite bismuth vanadate (BiVO4) are investigated using a combination of experiment and theory. We find that elemental hydrogen is present as an impurity in as-synthesized BiVO4 and that increasing its concentration by annealing in H2 at temperatures up to 290 °C leads to near-complete elimination of majority carrier transport limitations, a beneficial shift in the photoanodic current onset potential, and improved fill factor. Magnetic resonance measurements reveal that hydrogen can be incorporated in at least two different chemical environments, which are assigned to interstitial and substitutional sites. Incorporation of hydrogen leads to a shift of the Fermi level toward the conduction band edge, indicating that n-type character is correlated with increased hydrogen content. This finding is in agreement with theory and reveals that hydrogen acts as a donor in BiVO4. Sub-bandgap photoluminescence is observed from as-synthesized material and is consistent with deep electronic states associated with oxygen vacancies. Hydrogen treatment leads to reduced emission from these states. These findings support the conclusion that hydrogen, rather than oxygen vacancies, is dominant in determining the n-type conductivity of BiVO4. These findings have important implications for controlling the electronic properties and functional characteristics of this promising photoanode material.

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Section: Hydrogen Incorporation In Bivomentioning

confidence: 84%

Section: Hydrogen Incorporation In Bivomentioning

confidence: 99%

Role of Hydrogen in Defining the n-Type Character of BiVO₄ Photoanodes

Cooper¹,

Scott²,

et al. 2016

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“…As a result, T g decreases by ∼75 K at a mole fraction of 20% CaF 2 (10). Similar effects can also be achieved by replacing lattice oxygens with other anions such as H − and OH − (11). Processing C12A7 in a reducing environment leads to replacement of clathrated oxygens with electrons (12,13) (5,14,15).…”

mentioning

confidence: 64%

Electron anions and the glass transition temperature

Johnson

Sushko

Tomota

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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Properties of glasses are typically controlled by judicious selection of the glass-forming and glass-modifying constituents. Through an experimental and computational study of the crystalline, molten, and amorphous [Ca 12 Al 14 O 32 ] 2+ · (e -) 2 , we demonstrate that electron anions in this system behave as glass modifiers that strongly affect solidification dynamics, the glass transition temperature, and spectroscopic properties of the resultant amorphous material. The concentration of such electron anions is a consequential control parameter: It invokes materials evolution pathways and properties not available in conventional glasses, which opens a unique avenue in rational materials design.amorphous materials | glass transition | electrides | molecular dynamics | density functional theory O ne of the key challenges in materials design is identification of degrees of freedom that ensure robust control of the properties of interest. Small changes in composition of crystalline materials can lead to large changes in their electronic properties, such as optical absorption and electrical conductivity (1). Similarly, a small concentration of (co)dopants in amorphous materials can be used to control their optical properties (2, 3). Glass properties are typically controlled by varying composition or processing conditions (4). However, delicate control of viscosity and glass transition temperature in multicomponent materials (T g ) has remained elusive due to the collective origin of these properties. Substitution of atomic anions with electron anions in materials to form electrides (5, 6) introduces an additional degree of freedom. Here we demonstrate that electron anions dramatically change dynamics of atoms in an inorganic amorphous material, which strongly affects its T g . Extending the concept of electron anions to other amorphous materials would provide a powerful instrument for the design of glasses with finely tuned characteristics.Calcium aluminates (CA), composed of CaO and Al 2 O 3 , represent a common family of oxide glasses. Whereas pure Al 2 O 3 is a poor glass former, blending it with CaO leads to the formation of stable glasses composed of AlO 4 tetrahedra with strong and directional covalent bonds instead of nondirectional ionic bonds in bulk Al 2 O 3 (7). In contrast, Ca-O bonds retain their ionic character; they are weaker than Al-O bonds and lack a preferred orientation, which enables motion of the AlO 4 tetrahedra relative to each other. Hence, the T g of stoichiometric CA systems decreases by ∼50 K as the CaO content increases from 57 mol% to 70 mol% (Fig. 1). This relatively narrow interval of T g variation with composition is typical of multicomponent glasses (8, 9). The T g for stoichiometric [Ca 12 (5,14,15). In crystalline C12A7:e -, the electrons occupy the cage conduction band (CCB) states associated with the lattice cages (16, 17), leading to polaron-type conduction at x < ∼0.5 and metallic conduction at x > 0.5 (13, 16). The exceptionally low work function of crystalline C12A7:e -...

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“…It is crucial in the development of new type of cement as well as in solving various geological problems. The process of water incorporation was previously reported due to the scheme: Ca 12 Al 14 O 32 O + g H 2 O = Ca 12 Al 14 O 32 (OH) 2 , where two OH − groups occupying the W -site are stable up to 1500 K 26, 27 . However, temperatures associated with dehydration or dehydroxylation processes for these mineral phases have been not determined yet.…”

Section: Introductionmentioning

confidence: 99%

Different route of hydroxide incorporation and thermal stability of new type of water clathrate: X-ray single crystal and Raman investigation

Dulski

Marzec

Kusz

et al. 2017

Sci Rep

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Chlormayenite Ca12Al14O32[♦4Cl2] (♦-vacancy) is partially hydrated micro porouss mineral with hydroxide groups situated at various crystallographic sites. There are few mechanisms describing its hydration. The first one assumes Cl− substitution by OH− at the center of the structural cages (W-site). The second one determines the converting a T1O4 tetrahedron to a T1O3(OH)3 octahedron due to the replacement of oxygen at the O2 site by three OH-groups according to the scheme: (O2O2− + WCl−) → 3 × O2aOH. The third mechanism, not considered so far in the case of zeolite-like minerals, includes the hydroxide incorporation in form of hydrogarnet defect due to the arrangement of tetrahedral (OH)4 in vacant cages. This yields a strong hydrated phase containing even up to 35% of water more than in any currently known mineral applicable to Portland cement. Moreover, water molecules present in different structural cages are stable up to 355 K while dehydroxylation linked to the gradual loss of only 8% of OH− groups according to 3O2aOH− → O2O2− +WOH− + gH2O occurs at temperature range from 355 K to 598 K.

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Hydride ions in oxide hosts hidden by hydroxide ions

Cited by 113 publications

References 51 publications

Role of Hydrogen in Defining the n-Type Character of BiVO₄ Photoanodes

Role of Hydrogen in Defining the n-Type Character of BiVO₄ Photoanodes

Electron anions and the glass transition temperature

Different route of hydroxide incorporation and thermal stability of new type of water clathrate: X-ray single crystal and Raman investigation

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Hydride ions in oxide hosts hidden by hydroxide ions

Cited by 113 publications

References 51 publications

Role of Hydrogen in Defining the n-Type Character of BiVO4 Photoanodes

Role of Hydrogen in Defining the n-Type Character of BiVO4 Photoanodes

Electron anions and the glass transition temperature

Different route of hydroxide incorporation and thermal stability of new type of water clathrate: X-ray single crystal and Raman investigation

Contact Info

Product

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Role of Hydrogen in Defining the n-Type Character of BiVO₄ Photoanodes

Role of Hydrogen in Defining the n-Type Character of BiVO₄ Photoanodes