PHYSICAL REVIEW RESEARCH 2, 013328 (2020) Interface bonding of Zr1−xAlxN nanocomposites investigated by x-ray spectroscopies and first principles calculations (original) (raw)
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Bonding Structures of ZrHx Thin Films by X-ray Spectroscopy
Journal of Physical Chemistry C, 2017
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 aand d-phases, while sufficient hydrogen loading (x>1) yields a pure δphase 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.
Bonding Structures of ZrH x Thin Films by X-ray Spectroscopy
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.
Physical Review B, 2014
Despite the fast development of computational materials modelling, theoretical description of macroscopic elastic properties of textured polycrystalline aggregates starting from basic principles remains a challenging task. In this study we use a supercell-based approach to obtain the elastic properties of random solid solution cubic Zr1−xAlxN system as a function of the metallic sublattice composition and texture descriptors. The employed special quasi-random structures are optimised not only with respect to short range order parameters, but also to make the three cubic directions [1 0 0], [0 1 0], and [0 0 1] as similar as possible. In this way, only a small spread of elastic constants tensor components is achieved and an optimum trade-off between modelling of chemical disorder and computational limits regarding the supercell size and calculational time is proposed. The single crystal elastic constants are shown to vary smoothly with composition, yielding x ≈ 0.5 an alloy constitution with an almost isotropic response. Consequently, polycrystals with this composition are suggested to have Young's modulus independent on the actual microstructure. This is indeed confirmed by explicit calculations of polycrystal elastic properties, both within the isotropic aggregate limit, as well as with fibre textures with various orientations and sharpness. It turns out, that for low AlN mole fractions, the spread of the possible Young's moduli data caused by the texture variation can be larger than 100 GPa. Consequently, our discussion of Young's modulus data of cubic Zr1−xAlxN contains also the evaluation of the texture typical for thin films.
Physical Review B, 2017
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.
The structure, phase stability, and mechanical properties of ternary alloys of the Zr-Ta-N system are investigated by combining thin-film growth and ab initio calculations. Zr1−xTaxN films with 0≤x≤1 were deposited by reactive magnetron cosputtering in Ar+N2 plasma discharge and their structural properties characterized by x-ray diffraction. We considered both ordered and disordered alloys, using supercells and special quasirandom structure approaches, to account for different possible metal atom distributions on the cation sublattice. Density functional theory within the generalized gradient approximation was employed to calculate the electronic structure as well as predict the evolution of the lattice parameter and key mechanical properties, including single-crystal elastic constants and polycrystalline elastic moduli, of ternary Zr1−xTaxN compounds with cubic rocksalt structure. These calculated values are compared with experimental data from thin-film measurements using Brillouin light scattering and nanoindentation tests. We also study the validity of Vegard's empirical rule and the effect of growth-dependent stresses on the lattice parameter. The thermal stability of these Zr1−xTaxN films is also studied, based on their structural and mechanical response upon vacuum annealing at 850 °C for 3 h. Our findings demonstrate that Zr1−xTaxN alloys with Ta fraction 0.51⩽x⩽0.78 exhibit enhanced toughness, while retaining high hardness ∼30 GPa, as a result of increased valence electron concentration and phase stability tuning. Calculations performed for disordered or ordered structures both lead to the same conclusion regarding the mechanical behavior of these nitride alloys, in agreement with recent literature findings [H. Kindlund, D. G. Sangiovanni, L. Martinez-de-Olcoz, J. Lu, J. Jensen, J. Birch, I. Petrov, J. E. Greene, V. Chirita, and L. Hultman, APL Materials 1, 042104 (2013)].
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Journal of Physics: Condensed Matter, 2006
Mn 3d electronic states in the dilute magnetic semiconductor Zn 1−x Mn x S (x = 0.1-0.3) are studied using soft x-ray emission (XES) measurements and density functional theory (DFT). Mn L 2,3 emission spectra of Zn 1−x Mn x S (x = 0.1-0.3) suggest that the Mn impurities do not form clusters in the host ZnS lattice, in agreement with previous models. A shift in the position of a Mn L 3 XES feature suggests a change in the nature of the hybridization between the Mn 3d 3/2 and S 3p states as a function of x. Our DFT calculations reproduce the weak interatomic exchange interaction, as well as the strong intra-atomic exchange splitting that is expected from observations of Zeeman splitting in such materials.
Full-relativistic calculation of electronic structure of Zr2AlC and Zr2AlN
Solid State Communications, 2006
We have employed a full-relativistic version of an all-electron full-potential linearized-augmented plane-wave method in the local density approximation to investigate the electronic structure of nanolaminate Zr 2 AlX (X = C and N). The Zr 4d electrons are treated as valence electrons. We have investigated the lattice parameters, bulk moduli, band structures, total and partial densities of states and charge densities. It is demonstrated that the strength and electrical transport properties in these materials are principally governed by the metallic planes.
ACS applied materials & interfaces, 2017
Zn(O,S) buffer layer electronic configuration is determined by its composition and thickness, tunable through atomic layer deposition. The Zn K and L-edges in the X-ray absorption near edge structure verify ionicity and covalency changes with S content. A high intensity shoulder in the Zn K-edge indicates strong Zn 4s hybridized states and a preferred c-axis orientation. 2-3 nm thick films with low S content show a subdued shoulder showing less contribution from Zn 4s hybridization. A lower energy shift with film thickness suggests a decreasing bandgap. Further, ZnSO4 forms at substrate interfaces, which may be detrimental for device performance.
Фізика і хімія твердого тіла, 2019
The peculiarities of crystal and electronic structures, thermodynamic and energy state characteristics of the ZrNi1-xRhxSn semiconductive solid solution were investigated. It has been shown that in the ZrNiSn compound simultaneously exist two types of structural defects of the donor nature which generate two donor bands with different ionization energy in the band gap: a) the donor band ɛD1, formed as a result of a partial, up to ~ 1%, occupation of 4a position of Zr atoms by Ni atoms (mechanism of “a priori doping”) and deep donor band ɛD2, formed as a result of partial occupation of the tetrahedral voids by Ni atoms (Vac). The substitution in 4c position of the Ni atoms by Rh ones in ZrNi1-xRhxSn generates structural defects of acceptor nature and creates an impurity acceptor band ɛA in the band gap, which, in addition to the existence of ɛD1 та ɛD2 donor bands, makes semiconductor highly doped and strongly compensated. The obtained results allow to understand the mechanisms of el...