Role of oxygen in materials properties of yttrium trihydride

Pishtshev, Aleksandr; Karazhanov, Smagul

doi:10.1016/j.ssc.2014.06.012

Cited by 29 publications

(35 citation statements)

References 28 publications

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“…However, theoretical studies have demonstrated that a wide-band gap fcc phase, i.e. transparent-semiconducting, can be achieved at ambient conditions from the oxygenation of YH 3 or YH 2 films [20]. Since yttrium hydride films deposited by sputtering and exposed to air are known to 500 nm 500 nm YH YH oxidize heavily (see discussion below), the diffractogram measured for the YH x films cannot be unambiguously attributed to an YH 3 or YH 2 stoichiometry.…”

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confidence: 99%

Photochromic mechanism in oxygen-containing yttrium hydride thin films: An optical perspective

et al. 2017

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Oxygen-containing yttrium hydride thin films exhibit photochromic behavior: Transparent thin films reversibly switch from a transparent state to a photodarkened state after being illuminated with UV or blue light. From optical spectrophotometry and ellipsometry measurements of the transparent state and photodarkened state, it is concluded that the photochromic effect can be explained by the gradual growth, under illumination, of metallic domains within the initial wide-band-gap semiconducting lattice. This conclusion is supported by Raman measurements. DOI: 10.1103/PhysRevB.95.201301 Oxygen-containing yttrium hydride films exhibit photochromic (PC) behavior, i.e., the optical properties of the films change reversibly when illuminated by light of adequate energy (wavelengths in the blue or UV range). Early works by Hoekstra et al. [1] reported photoconductivity in yttrium hydrides at low temperature, and Ohmura et al. [2,3] accidentally discovered PC behavior in yttrium hydride films subjected to high pressure. In addition, Huiberts et al. observed for the first time the gasochromic behavior of yttrium hydride thin films [4]. Later, Mongstad et al. [5,6] reported PC behavior in transparent oxygen-rich yttrium hydride films under atmospheric conditions and at room temperature. In the latter case, however, the yttrium hydride films were directly obtained by reactive magnetron sputtering rather than by the subsequent hydrogenation of a predeposited metallic Y layer. Oxygen-rich yttrium hydride is not the only oxygen-containing hydride which exhibits interesting physical properties. For instance, Miniotas et al. have reported gigantic resistivity and band-gap changes in oxygen-containing gadolinium hydride [7].The mechanism of the PC behavior in oxygen-rich yttrium hydride is still unclear and seems to have no relation to the PC mechanism reported for transition-metal oxides [8]. In the present Rapid Communication, the properties of oxygen-rich transparent semiconducting yttrium hydride thin films-hereafter referred to as YH x O sc w , where the superscript sc refers to their semiconducting character-and of opaque metallic yttrium hydride thin films-from now on referred to as YH y O m z , where y < x and where the superscript m refers to their metallic character-have been investigated by grazing incidence x-ray diffraction (GIXRD), Raman spectroscopy, ellipsometry, and spectrophotometry. Both sets of films, YH x O sc w and YH y O m z , were deposited onto soda-lime glass substrates by sputter deposition at a hydrogen/argon ratio = 0.18 and 0.13, respectively, and then exposed to air where they oxidize. A detailed description of the deposition method can be found in our previous work [9] Chandran et al. [8], which reports changes of the hydrogen species in oxygen-containing yttrium hydride after illumination, suggesting the release of electrons and the formation of a metallic phase.Figure 1(a) shows GIXRD patterns-obtained by using Cu Kα radiation at a fixed angle of incidence of 2• in a Bruker Siemens D5000 diffr...

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Photochromic mechanism in oxygen-containing yttrium hydride thin films: An optical perspective

et al. 2017

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“…YHO films contain two types of competing anions, oxygen and hydrogen, both connected to yttrium atoms . By performing the deposition at different H 2 /Ar flow rates and then oxidizing the films, it is possible to obtain YHO thin films with different concentrations of anion vacancies as well as of hydrogen and oxygen anions with [H] and [O] concentrations anti‐correlated with each other.…”

Section: Resultsmentioning

confidence: 99%

Photoluminescence Properties of Photochromic Yttrium Hydride Films Containing Oxygen

Montero

Galeckas

Karazhanov

2018

Physica Status Solidi (b)

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Oxidation of YH xAEδ modulates its optical properties by converting it from optically opaque to transparent state to the visible light and electrical properties from metallic conductivity to insulating. The qualitative change of the materials properties are related to oxidation-induced modulation of electronic properties of the material that will influence the band gap and luminescence properties of the oxygen-containing yttrium hydride (YHO). This work presents the optical properties, studied by optical spectrophotometry and photoluminescence spectroscopy, of YHO thin films deposited by reactive magnetron sputtering at different H 2 /Ar flow ratios between 0.18 and 0.28. The indirect and direct band gap of the YHO photochromic films in their clear state is estimated from optical absorption measurements performed at room temperature, and found in the range between 2.5 and 2.6 eV (indirect allowed transition) and between 3.0 and 3.3 eV (direct allowed transition). The study of photoluminescence (PL) properties is performed in the temperature range between 10 and 300 K. The luminescence yield corresponding to the clear state was found to be extremely low in all the YHO films, and it reduced even further once the films darkened under UV-light exposure. The PL emission at room temperature covers the entire UV and visible range, comprising two broad bands centered at around 2.2 and 3.1 eV. The latter band became fine-structured at low-temperatures (10 K), showing a series of distinct PL peaks at energy positions between 2.8 and 3.4 eV which were independent of the H 2 /Ar flow ratio used during deposition. By the comparison of the PL measurements conducted in vacuum with the ones performed in air, it is possible to conclude that the environment plays an important role in the photochromic properties of YHO. The possible intrinsic and extrinsic origin of the structured PL emission is discussed in terms of excitonic features and/or luminescent surface defects. We report that the main optical transitions of the films deposited at different H pressures did not change by variation of temperature or by UV light-induced color change.

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“…In the oxidation of yttrium hydrides, because of a stronger affinity of elemental yttrium for oxygen and its preference to exhibit 3+ oxidation state, there appears the concurrency between the incorporated oxygen and host hydrogen for connectivity with the metal center. Since the metal prefers to bind the oxygen atom, the oxidization process of the hydride system is accompanied by two factors: (i) the change of initial valence electron configurations proceeding in terms of delocalization-localization conversion and (ii) a chain of structural transformations leading to a stable condensed phase [72]. One can, therefore, suggest that, when His topochemically replaced by oxygen, the interplay of processes, such as the Y−H covalent bond cleavage and the Y−O ionic bond formation, may keep a certain part of the interstitial hydrogen species in the lattice.…”

Section: Crystal Assembly In Terms Of Structural Transformationsmentioning

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On Prediction of a Novel Chiral Material Y2H3O(OH): A Hydroxyhydride Holding Hydridic and Protonic Hydrogens

2020

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Examination of possible pathways of how oxygen atoms can be added to a yttrium oxyhydride system allowed us to predict new derivatives such as hydroxyhydrides possessing the composition M2H3O(OH) (M = Y, Sc, La, and Gd) in which three different anions (H-, O2−, and OH-) share the common chemical space. The crystal data of the solid hydroxyhydrides obtained on the base of DFT modeling correspond to the tetragonal structure that is characterized by the chiral space group P 4 1 . The analysis of bonding situation in M2H3O(OH) showed that the microscopic mechanism governing chemical transformations is caused by the displacements of protons which are induced by interaction with oxygen atoms incorporated into the crystal lattice of the bulk oxyhydride. The oxygen-mediated transformation causes a change in the charge state of some adjacent hydridic sites, thus forming protonic sites associated with hydroxyl groups. The predicted materials demonstrate a specific charge ordering that is associated with the chiral structural organization of the metal cations and the anions because their lattice positions form helical curves spreading along the tetragonal axis. Moreover, the effect of spatial twisting of the H- and H+ sites provides additional linking via strong dihydrogen bonds. The structure–property relationships have been investigated in terms of structural, mechanical, electron, and optical features. It was shown that good polar properties of the materials make them possible prototypes for the design of nonlinear optical systems.

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Role of oxygen in materials properties of yttrium trihydride

Cited by 29 publications

References 28 publications

Photochromic mechanism in oxygen-containing yttrium hydride thin films: An optical perspective

Photochromic mechanism in oxygen-containing yttrium hydride thin films: An optical perspective

Photoluminescence Properties of Photochromic Yttrium Hydride Films Containing Oxygen

On Prediction of a Novel Chiral Material Y2H3O(OH): A Hydroxyhydride Holding Hydridic and Protonic Hydrogens

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