Structural, mechanical and electronic properties of transition metal hydrides MH2 (M = Ti, Zr, Hf, Sc, Y, La, V and Cr)

Chihi, T.; Fatmi, M.; Bouhemadou, A.

doi:10.1016/j.solidstatesciences.2012.02.010

Cited by 21 publications

(17 citation statements)

References 11 publications

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“…In our x-ray absorption study [34], a chemical shift towards higher energies in comparison to Zr metal was found to be due to changes in the oxidation state that depends on the structure and the formation of Zr-H bonding at sufficient hydrogen loading. Previous valence band XPS experiments have shown a dominant Zr 4d peak at 1 eV and another peak around 6.4 eV corresponding to a Zr-H bond [35], consistent with DOS calculations [31] [29] [30]. The chemical shift of the Zr edges towards higher bonding energies confirms a significant charge-transfer from Zr towards H with increasing hydrogen content.…”

Section: Resultssupporting

confidence: 85%

Electronic properties and bonding in ZrHx thin films investigated by valence-band x-ray photoelectron spectroscopy

et al. 2017

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The electronic structure and chemical bonding in reactively magnetron sputtered ZrH x (x = 0.15, 0.30, 1.16) thin films with oxygen content as low as 0.2 at.% are investigated by 4d valence band, shallow 4p core-level, and 3d core-level x-ray photoelectron spectroscopy. With increasing hydrogen content, we observe significant reduction of the 4d valence states close to the Fermi level as a result of redistribution of intensity toward the H 1s-Zr 4d hybridization region at ∼6 eV below the Fermi level. For low hydrogen content (x = 0.15, 0.30), the films consist of a superposition of hexagonal closest-packed metal (α phase) and understoichiometric δ-ZrH x (CaF 2 -type structure) phases, while for x = 1.16, the films form single-phase ZrH x that largely resembles that of stoichiometric δ-ZrH 2 phase. We show that the cubic δ-ZrH x phase is metastable as thin film up to x = 1.16, while for higher H contents the structure is predicted to be tetragonally distorted. For the investigated ZrH 1.16 film, we find chemical shifts of 0.68 and 0.51 eV toward higher binding energies for the Zr 4p 3/2 and 3d 5/2 peak positions, respectively. Compared to the Zr metal binding energies of 27.26 and 178.87 eV, this signifies a charge transfer from Zr to H atoms. The change in the electronic structure, spectral line shapes, and chemical shifts as a function of hydrogen content is discussed in relation to the charge transfer from Zr to H that affects the conductivity by charge redistribution in the valence band.

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Section: Resultssupporting

confidence: 85%

Electronic properties and bonding in ZrHx thin films investigated by valence-band x-ray photoelectron spectroscopy

et al. 2017

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“…From the position of the 111 peak in the q/2q diffractogram recorded from the ZrH 1.16 film, it was possible to determine the a-axis to 4.808 Å. This is slightly larger than the literature value for bulk d-ZrH 2 with 4.781 Å 25 , but somewhat smaller than the calculated values by Chihi et al 14 A possible explanation for the deviation from bulk is that the film is in a state of stress due to the intense flux of sputtered material applied during growth seen from a deposition rate of ~70 Å/s 13 . This high growth kinetics with energetic ions and atoms normally cause defects in thin films with excess volume (atomic peening) and surface diffusion into cusps causing compressive stress.…”

Section: Xanes and Exafs Measurementsmentioning

confidence: 55%

Bonding Structures of ZrH_x Thin Films by X-ray Spectroscopy

et al. 2017

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The variation in local atomic structure and chemical bonding of ZrH x (x=0.15, 0.30, 1.16) magnetron sputtered thin films are investigated by Zr K-edge (1s) X-ray absorption near-edge structure and extended X-ray absorption fine structure spectroscopies. A chemical shift of the Zr K-edge towards higher energy with increasing hydrogen content is observed due to charge-transfer and an ionic or polar covalent bonding component between the Zr 4d and the H 1s states with increasing valency for Zr. We find an increase in the Zr-Zr bond distance with increasing hydrogen content from 3.160 Å in the hexagonal closest-packed metal (a-phase) to 3.395 Å in the understoichiometric d-ZrH x film (CaF 2 -type structure) with x=1.16 that largely resembles that of bulk d-ZrH 2 . For yet lower hydrogen contents, the structures are mixed a-and d-phases, while sufficient hydrogen loading (x>1) yields a pure δ-phase that is understoichiometric, but thermodynamically stable. The change in the hydrogen content and strain is discussed in relation to the corresponding change of bond lengths, hybridizations, and trends in electrical resistivity.

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“…The calculated density of state at the Fermi level reported in these studies support experimental results on good electrical conductivity for both phases and the calculations show that the d-bands of zirconium play a dominant role in the electrical transport. The chemical bonding in δ-ZrH 2 and ε-ZrH 2 is characterized by strong interaction between zirconium and hydrogen, and in the works by Zhang et al 8 and Chihi et al 9 it is concluded that the Zr-H bonding exhibits higher degree of ionic character than covalent type of bonding. A less directional bond is also to be expected in zirconium hydrides compared to for instance ZrC and ZrN, since the interaction occurs between Zr d-orbitals and H s-orbital in the hydride, while the high hardness values and extreme melting points found for carbides and nitrides stem from the interaction between the metal d-orbitals and the highly directional p-orbitals of carbon or nitrogen.…”

Section: Introductionmentioning

confidence: 98%

“…7 . 1 Using firstprinciple calculations of the electronic structures for δ-ZrH 2 and ε-ZrH 2 , the electrical and mechanical properties have been assessed [6][7][8][9] . The calculated density of state at the Fermi level reported in these studies support experimental results on good electrical conductivity for both phases and the calculations show that the d-bands of zirconium play a dominant role in the electrical transport.…”

Section: Introductionmentioning

confidence: 99%

Reactive sputtering of δ-ZrH2 thin films by high power impulse magnetron sputtering and direct current magnetron sputtering

Högberg¹,

Tengdelius²,

Samuelsson³

et al. 2014

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

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Reactive sputtering by high power impulse magnetron sputtering (HiPIMS) and direct current magnetron sputtering (DCMS) of a Zr target in Ar/H 2 plasmas was employed to deposit Zr-H films on Si(100) substrates, and with H content up to 61 at.% and O contents typically below 0.2 at.% as determined by elastic recoil detection analysis. X-ray photoelectron spectroscopy reveals a chemical shift of 0.7 eV to higher binding energies for the Zr-H films compared to pure Zr films consistent with a charge transfer from Zr to H in a zirconium hydride. X-ray diffraction shows that the films are single-phase δ-ZrH 2 (CaF 2 -type structure) at H content > 55 at.% and pole figure measurements give a 111 preferred orientation for these films.Scanning electron microscopy cross-section images show a glasslike microstructure for the HiPIMS films, while the DCMS films are columnar. Nanoindentation yield hardness values of 5.5-7 GPa for the δ-ZrH 2 films that is slightly harder than the 5 GPa determined for Zr films and with coefficients of friction in the range 0.12-0.18 to compare with the 0.4-0.6 obtained 2 for Zr films. Wear resistance testing show that phase-pure δ-ZrH 2 films deposited by HiPIMS exhibit up to 50 times lower wear rate compared to those containing a secondary Zr phase.Four-point probe measurements give resistivity values in the range of 100-120 µΩ cm for the δ-ZrH 2 films, which is slightly higher compared to Zr films with values in the range 70-80 µΩ cm.

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Structural, mechanical and electronic properties of transition metal hydrides MH2 (M = Ti, Zr, Hf, Sc, Y, La, V and Cr)

Cited by 21 publications

References 11 publications

Electronic properties and bonding in ZrHx thin films investigated by valence-band x-ray photoelectron spectroscopy

Electronic properties and bonding in ZrHx thin films investigated by valence-band x-ray photoelectron spectroscopy

Bonding Structures of ZrH_x Thin Films by X-ray Spectroscopy

Reactive sputtering of δ-ZrH2 thin films by high power impulse magnetron sputtering and direct current magnetron sputtering

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Structural, mechanical and electronic properties of transition metal hydrides MH2 (M = Ti, Zr, Hf, Sc, Y, La, V and Cr)

Cited by 21 publications

References 11 publications

Electronic properties and bonding in ZrHx thin films investigated by valence-band x-ray photoelectron spectroscopy

Electronic properties and bonding in ZrHx thin films investigated by valence-band x-ray photoelectron spectroscopy

Bonding Structures of ZrHx Thin Films by X-ray Spectroscopy

Reactive sputtering of δ-ZrH2 thin films by high power impulse magnetron sputtering and direct current magnetron sputtering

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Bonding Structures of ZrH_x Thin Films by X-ray Spectroscopy