Despite the fact that chemists frequently draw electron density distributions, there are few good methods for measuring this quantity, which has contributed to many longstanding controversies in chemistry. In this paper, we report the first application of element specific L absorption spectra and the “white light” sum rule to a series of nickel complexes, with wide oxidation state range from NiI to NiIV. Nickel L edge X-ray absorption spectroscopy is turning out to be an excellent quantitative probe of 3d-vacancies.

X-ray absorption spectra have been measured for NiO, β-Ni(OH) 2 , R-Ni(OH) 2 , LiNiO 2 , and KNiIO 6 samples, which contain nickel with valency in the range 2-4. Information on the local structure and nature of bonding of nickel compounds has been derived using theoretical standards generated with the FEFF code. The Ni K-edge energy was found to shift to higher values by about 1.5 eV per unit change in valency of nickel. The energy of the preedge peak (generally attributed to the transition from the 1s core states to the 3d unoccupied states) shifts to higher values by about 0.6 eV per unit change in valency of nickel. A many body amplitude reduction factor (S 0 2 ) of 0.77 ( 0.03 for Ni K-edge absorption can be used to scale theoretical spectra to fit the experimental ones in order to accurately determine the coordination numbers for compounds with complex structures. Our results show that chemical effects are very small and can be ignored for reliable structural analysis. Results of local structure for the first, second, and third coordination spheres for NiO are consistent with those derived from X-ray diffraction data. The results for β-Ni(OH) 2 are much closer in agreement with those derived from the neutron diffraction data rather than the X-ray diffraction data. The results for R-Ni(OH) 2 differ significantly from those based on the idealized structure model proposed by Bode et al. In fact, the structure within the hexagonal planes for R-Ni(OH) 2 is similar to that for β-Ni(OH) 2 . The apparent contraction in the Ni-Ni distance of the third coordination sphere for R-Ni(OH) 2 relative to that for β-Ni-(OH) 2 , which was previously reported by others, is not real and can be attributed to structural disorder. The Ni-O bond length for divalent nickel with an octahedral coordination is in the range 2.06-2.08 Å. The first coordination sphere for LiNiO 2 consists of four and two oxygens at 1.91 and 2.06 Å, respectively, rather than six oxygens at 2.04 Å, as predicted by the X-ray diffraction data. The short distance is characteristic of Ni 3+ -O 2bonds and Ni 2+ -O -bonds, while the long distance is characteristic of Ni 2+ -O 2bonds. The local structure for LiNiO 2 is consistent with the fact that the charge-compensating mechanism is largely due to oxygen 2p holes. The Ni-Ni second-shell distance for LiNiO 2 is consistent with that based on the X-ray and neutron diffraction data. The Ni-O bond length for quadrivalent Ni in KNiIO 6 is 1.88 Å. The Ni-O bond length varies with nickel valency in a nonlinear manner.

Raman spectra are reported for consolidated nanophase TiO2 particles in their as-compacted state and after annealing at a variety of temperatures up to 1273 K. The Raman-active bands normally observed for the rutile form of TiO2 were present in as-compacted samples having average grain sizes in the range from about 10 to 100 nm. However, significant broadening of these bands was found, which was uncorrelated with initial grain size, but not necessarily with other synthesis-related factors. This broadening decreased upon isochronal annealing at elevated temperatures in air. Based upon these observations, it is concluded that nanophase TiO2 in the as-consolidated state contains significant defect concentrations within the rutile grains and that these intragrain defects and the grain-boundary regions as well have local atomic structures with the rutile symmetry, albeit with some short-range displacements. Some sporadic sample regions containing small amounts (<5%) of the anatase form of TiO2 were also found; these traces of anatase transformed to rutile upon annealing in air at temperatures above 883 K.

We report x-ray photoemission spectra ͑XPS͒ of electrochemically prepared ␥-NiOOH. XPS spectra were measured with the Physical Electronics Model 5400 x-ray photoelectron spectrometer using unmonochromatized Mg K ␣ x rays at two pass energy settings corresponding to analyzer energy resolutions of 1.34 and 0.54 eV. We present the survey spectrum ͑binding energy range of 0-1100 eV͒ measured at an analyzer energy resolution of 1.34 eV. Multiplexes of the C, O, K, and Ni photoemission lines, valence band region, as well as Ni LMM Auger line were measured at an analyzer energy resolution of 0.54 eV. The ␥-NiOOH sample was prepared by the anodic oxidation of anodically formed ␣-Ni͑OH͒ 2 .

We have utilized X-ray absorption fine structure (XAFS) spectroscopy to investigate the local atomic and electronic structure of iron incorporated into electrodeposited nickel hydroxide films. We found that cathodic codeposition from a solution containing Fe(II) and Ni(II) ions results in iron occupying Ni lattice sites in R-Ni(OH) 2 . The X-ray absorption near edge structure (XANES) shows that Fe is present as Fe(III) ions in the cathodically codeposited film. Analysis of the extended X-ray absorption fine structure (EXAFS) shows that Fe is coordinated to oxygen at ∼2.00 Å and to Ni at ∼3.11 Å. This Fe-O bond length is smaller than the Fe(II)-O bond distance found in Fe(OH) 2 (∼2.10 Å) but is in good agreement with the average Fe-(III)-O bond distance found in FeOOH (R, γ). The Fe-Ni bond distance is in agreement with that of the Ni(II)-Ni(II) bond distance found in R-Ni(OH) 2 . Moreover, the radial structure function (RSF) around Fe shows a distinct peak at ∼5.8 Å, which is a fingerprint of the brucite (R-Ni(OH) 2 ) structure. On anodic oxidation of the codeposited film in KOH, we found that the Fe ions occupied Ni lattice sites in γ-NiOOH.The XANES shows that the Fe edge shifts to higher energy values, indicating an increase in the oxidation state of Fe on charging. Analysis of the EXAFS data shows that Fe is coordinated to oxygen at ∼1.94 Å and to Ni at ∼2.84 Å. The latter value is in good agreement with the Ni(IV)-Ni(IV) bond length found in γ-NiOOH. The RSF around Fe in the oxidized film shows a distinct peak at ∼5.4 Å, just as in the RSF of Ni in γ-NiOOH. The Fe-O bond distance of ∼1.94 Å is in good agreement with the Fe(IV)-O bond distance found in SrFeO 3 . Our results strongly suggest that the Fe ions in the oxidized film is nominally tetravalent but with the Fe-O bond possessing a high degree of covalency.

We have measured in situ the Ni K‐edge X‐ray absorption spectra of Lifalse(1−zfalse)Nifalse(1+zfalse)O2 cathode material charged in a nonaqueous cell. The material was charged to various states of charge (i.e., Li content) which corresponded to x = 0.0, 0.12, 0.24, 0.37, 0.49, and 0.86 in Lifalse(1−x−zfalse)Nifalse(1+zfalse)O2 . We have determined variations in the Ni‒O and Ni‒Ni coordination numbers, bond lengths, and local disorders as well as the Ni K‐edge energies as a function of Li content. We show that in the pristine state, the composition of the material can be described by the formula Li0.86Ni1.14O2 (i.e., x = 0 and z = 0.14). That is, the material consists of Ni2+ (25%) and Ni3+ (75%) with half the Ni2+ atoms residing in Li sites and the other half in the NiO2 slabs. Upon charging, initially Ni2+ is oxidized to Ni3+ up to a state of charge which corresponds to x = 2 z . Upon further charging to states corresponding to 2z

In situ laser Raman spectra of anodic corrosion films formed on Ni and Co in 0.05M NaOH have been obtained for the first time and the composition of the surface films deduced. The Raman spectrum of the film found on Ni at about 0.6V vs. Hg/HgO corresponds closely to that of hydrated Ni20~. The anodically formed film on Co at about 0.45V appeared to consist of a mixture of CoO and Co304.

We report x-ray photoemission spectra ͑XPS͒ of beta-nickel hydroxide ͑␤-Ni͑OH͒ 2 ͒. XPS spectra were measured with the Physical Electronics Model 5400 x-ray photoelectron spectrometer using unmonochromated Mg K ␣ x rays at two pass energy settings corresponding to analyzer energy resolutions of 1.34 and 0.54 eV. We present the survey spectrum ͑binding energy range of 0-1100 eV͒ measured at an analyzer energy resolution of 1.34 eV. Multiplexes of the C, O, and Ni photoemission lines, valence band region as well as the Ni LVV Auger lines were measured at an analyzer energy resolution of 0.54 eV. The research grade high purity ␤-Ni͑OH͒ 2 sample was obtained commercially from Chemical Company, Inc.