Transition Of NiO Research Articles

Adsorption of phosphate ions from water using PVA-NiO nanocomposite based on tuning influence of pulsed laser ablation method

For the purpose of getting rid of phosphate in the direction of preserving the eco-system, nickel oxide nanoparticles (NiO NPs) have recently been used to address this issue. For that, NiO NPs were generated using a laser ablation in liquid method of PVA solution and encapsulated in a PVA matrix structure with different particle sizes using a nanosecond solid-state laser with a change in laser influence. Then, their physicochemical properties were studied using various methods. It was found that NiO NPs were distributed very well inside the PVA structure, which was confirmed by the presence of both characteristic vibrational peaks of PVA and NiO with shifting in the peak of PVA and the appearance of the main characteristic transition peaks of the d-d transition of NiO, relating to the impedance of the PVA structure with NiO NPs. The optimal conditions for the elimination of phosphate ions from water solutions were determined by examining the impacts of a number of important affected parameters. A concentration of 100 mg L−1 of phosphate can be removed from a liquid medium at pH 6 using a PVA-NiO nanocomposite. This work lays the route to getting on different nanocomposite materials to get rid of different hazardous chemical compounds.

Symmetry considerations on band filling and first optical transition in NiO

Recent theoretical works on NiO have not agreed upon the nature of the first optical transition. By altering band filling – with highly concentrated O vacancies and Fe impurities – here, the orbital density of states is changed near the Fermi energy. The variation in optical properties, relative to the changes in orbital character, along with group theory analysis of hybridized orbitals, provides new insight when evaluating the first optical transition of NiO. Here, based on density functional theory, the first optical transition is found to have two possibilities – either superexchange site-hopping or a transition from the hybridized eg state to the hybridized a1u state, rather than the intra-atomic transitions which are causing disagreement in the recent literature.

Low energy excitations in NiO based on a direct Δ-SCF approach

This paper reports calculated energies and electronic structures of nineteen excited states in NiO based on a Δ-SCF approach reported previously for the transitions in NiO and Sr2CuO2Cl2. They are the spin-flip: ; eight : (one electron) 3A2g → 3T2g, (two electron) 3A2g → 3T1g, 3A2g → a1Eg, 3A2g → 1T2g, 3A2g → 1T1g, 3A2g → b1Eg, 3A2g → b1T2g; two O(2p) → Ni(3d); seven Ni(3d) → O(2p) (including two spin-flip) and the O(2s) → Ni(3d) charge transfer excitations, which span an energy range from 0.25 eV to 17.53 eV, and include the fundamental band gap associated with an excitonic O(2p) → Ni(3d) transition at 4.23 eV. These are compared to absorption and emission spectra, and previous calculations. In the case of the O(2p) → Ni(3d) excitations, comparisons are given for gap and Γ-point energies derived from HF, PBE0, HSE06, B3LYP, B1WC, GGA and LDA one-electron approximations. Finally, the directly calculated Stokes shifts and associated luminescence energies for the two O(2p) → Ni(3d) transitions are reported, where the excitonic value is found to be in good agreement with the recently reported experimental value.

Magnetostructural phase transitions in NiO and MnO: Neutron diffraction data

Structural and magnetic phase transitions in NiO and MnO antiferromagnets have been studied by high-precision neutron diffraction. The experiments have been performed on a high-resolution Fourier diffractometer (pulsed reactor IBR-2), which has the record resolution for the interplanar distance and a high intensity in the region of large interplanar distances; as a result, the characteristics of both transitions have been determined simultaneously. It has been shown that the structural and magnetic transitions in MnO occur synchronously and their temperatures coincide within the experimental errors: Tstr ≈ Tmag ≈ (119 ± 1) K. The measurements for NiO have been performed with powders with different average sizes of crystallites (~1500 nm and ~138 nm). It has been found that the transition temperatures differ by ~50 K: Tstr = (471 ± 3) K, Tmag = (523 ± 2) K. It has been argued that a unified mechanism of the “unsplit” magnetic and structural phase transition at a temperature of Tmag is implemented in MnO and NiO. Deviation from this scenario in the behavior of NiO is explained by the quantitative difference—a weak coupling between the magnetic and secondary structural order parameters.

Structural study of Novel (superhard) material: NiO

We have investigated the pressure-induced phase transition of NiO and other structural properties using three-body potential approach. NiO undergoes phase transition from B1 (rocksalt) to B2 (CsCl) structure associated with a sudden collapse in volume showing first-order phase transition. A theoretical study of high pressure phase transition and elastic behaviour in transition metal compounds using a three-body potential caused by the electron shell deformation of the overlapping ion was carried out. The phase transition pressure and other properties predicted by our model is closer to the phase transition pressure predicted by Eto et al.

Full hemispherical intensity maps of crystal field transitions in NiO(001) by angular resolved electron energy loss spectroscopy

In electron energy loss spectroscopy (EELS), the excitation of crystal field transitions in 3d transition metal oxides takes place via two scattering mechanisms, i.e. direct scattering as well as electron exchange scattering. In addition to spin-polarized EELS, spin-integrated but angular resolved experiments may be helpful to distinguish between exchange scattering and direct scattering using the angular dependence of their scattering amplitudes. Intensity maps of crystal field transitions over the whole 2π solid angle of NiO show characteristic features that can be attributed to the contributions of both scattering amplitudes. It was found that the energy loss at Δ E=2.7 eV, which consists mainly of triplet–singlet transitions and is therefore excited only by electron exchange, shows the angular characteristics that were predicted by theory for the spin flip part of the scattering amplitude. In contrast, the angular dependence of the triplet–triplet transition at Δ E=1.6 eV, which is excited via direct scattering as well as exchange scattering, is similar to the LEED pattern of the zero loss peak, i.e. the dipole-like forward scattering is modulated by reciprocal lattice vectors.

Resonant electron-exchange excitations in transition-metal oxides

Electron-exchange processes in dipole-forbidden $d\ensuremath{-}d$ excitations of the $3d$ transition-metal oxides NiO, CoO, and MnO have been investigated by spin-polarized electron-energy-loss spectroscopy over a wide primary energy range and for different scattering geometries. At primary energies corresponding to certain excitation thresholds, the $d\ensuremath{-}d$ excitations in CoO and MnO show resonant enhancement, similar to the resonances previously found for NiO. The resonance around 38 eV, which is assigned to simultaneous excitations within the $d$-multiplet and oxygen excitations, occurs at nearly identical primary energy, due to identical energetic positions of the oxygen levels in the three oxides. The metal $3s\ensuremath{-}3d$ resonance is shifted toward lower energy in CoO and MnO, according to the lower binding energies of the $3s$ levels. In resonance, the $d\ensuremath{-}d$ excitations are highly exchange dominated. Off resonance, a strong superposition with direct dipole-scattering processes has been found for the dominant multiplicity-conserving transitions in NiO and CoO. Excitation by direct dipole scattering is completely missing in the spin-forbidden, multiplicity-changing transitions in MnO.

Resonant electron exchange scattering in late transition metal monoxides

Abstract Intra-atomic d-d transitions in NiO(100) and CoO(100) have been investigated with angle-resolved electron energy loss spectroscopy (EELS) at primary energies close to the metal 3s excitation threshold. Electron exchange scattering was found to be resonantly enhanced at the 3s threshold due to the temporary formation of a negative ion core state and its subsequent decay via Auger-like transitions. In both oxides the threshold is lowered several eV due to a strong electron- core hole interaction. Angle-dependent studies reveal a different dependency of exchange processes on the scattering angle as compared with nonresonant measurements and reveal a different angle dependence for each specific d-d transition. It is suggested that in these oxides large-angle single-step inelastic scattering contributes significantly to the EELS measurements in reflection mode.

Localized d-d excitations in NiO(100) and CoO(100).

The localized character of the 3d electrons in the antiferromagnetic oxides NiO(100) and CoO(100) has been studied with electron energy-loss spectroscopy at primary energies between 20 and 1200 eV. The spectra of both charge-transfer compounds exhibit weak but sharp loss structures within the insulating gap region due to crystal-field excitations of the 3${\mathit{d}}^{\mathit{n}}$ configuration (${\mathit{d}}^{\mathit{n}}$\ensuremath{\rightarrow}${\mathit{d}}^{\mathit{n}\mathrm{*}}$). These parity forbidden d-d excitations are strongly enhanced at low primary energies due to exchange scattering. Their observed loss intensity depends on the momentum transfer at the scattering process as is shown by angle-dependent measurements. At NiO(100) a surface d state is found that is due to the lower symmetry of the ligand field at the surface. The measurements demonstrate the existence of spin-forbidden exchange excitations $^{3}$${\mathit{A}}_{2\mathit{g}}$\ensuremath{\rightarrow}${(}^{1}$${\mathit{E}}_{\mathit{g}}$${,}^{1}$${\mathit{T}}_{1\mathit{g}}$) in NiO(100) and reveal their excitation energies. A resonant enhancement of all intra-atomic d-d transitions in NiO(100) is found at the Ni 3s excitation threshold. Temperature-dependent measurements up to the N\'eel point show only little influence of the antiferromagnetic ordering on the EELS spectra of NiO(100). The different shapes of the absorption edges due to interatomic d-d transitions across the insulating gaps of NiO(100) and CoO(100) are discussed.

Zur Hyperfeinstruktur von 111Cd in Metalloxiden

AbstractThe Perturbed Angular Correlation method was applied to measure the hyperfine interaction of the 111Cd‐nucleus after implantation of its radioactive mother isotope 111ln (≈ 1012 ions at E ≈ 400 keV) into various metal‐oxides (NiO, CuO, AgO, Cu2O, Ag2O, Al2O3, Cr2O3, In2O3, Rh2O3). In most cases we were able to identify 111Cd on substitutional sites in a defect‐free oxide surrounding by proper thermal annealing of our samples. The capability of the PAC method to resolve small changes in the microsurrounding will be demonstrated by the results of our experiments on In2O3. Exemplary, the application of the technique to the observation of magnetical, structural and chemical phase transitions in NiO, Rh2O3, AgO and CuO will be discussed. By comparing the experimental values with a simple point charge model, a systematic behaviour of the electric field gradients was found.

Ab initio SCF and limited CI calculations on the d-d transitions in NiO

SCF and limited CI calculations on d-d transitions in NiO are presented. The calculations were performed on NiO6 10-, stabilized by an electrostatic field. Closed Ni d-orbitals turned out delocalized from the calculations, but this was found to be an artifact of the calculation. The CI calculation showed that the d-electrons are in fact well localized on the metal, and that this localization may be obtained after pairwise rotations between the appropriate delocalized orbitals. The configuration interaction results are thus insensitive to the choice of reference state, provided that excitations describing the pairwise rotation are included in the CI expansion; only minor effects were obtained when excited-state orbitals instead of ground state orbitals were used in the calculations. A crystal-field treatment, based on SCF wave functions, yielded excitation energies in good agreement with the CI results. The computed results are satisfactory and the order 3 A 2g , 3 T 2g , 3 T 1g and 1 Eg is proposed for the ground and first three excited states.

Optical anisotropy measurements in multidomain samples: Application to phase transitions in NiO and Pb5Ge3O11

Optical anisotropy measurements in multidomain samples: Application to phase transitions in NiO and Pb5Ge3O11