Electrochemical, X-ray diffraction, and K and L edge X-ray absorption data are reported for the layered cathode material Li 1.2 Mn 0.4 Cr 0.4 O 2 . The structural data show that this material can be understood as a solid solution of the layered phases Li 2 MnO 3 and LiCrO 2 , comprising tretravalent Mn and trivalent Cr, with approximately 0.2 lithium incorporated in the transition metal layers. According to the analysis of the K edge extended X-ray absorption fine structure, lithium ions in the transition metal layers are clustered around Mn ions. L edge X-ray absorption near edge spectra show that in the first charge-discharge cycle chromium is the electrochemically active species, cycling between Cr 3ϩ and Cr 6ϩ . Manganese remains as Mn 4ϩ throughout charge and discharge.Layered lithium manganese oxides are of interest as cathodes for rechargeable lithium batteries due to the safety, low cost, and low toxicity of manganese-based materials. However, basic problems such as the collapse of the layer structure toward the spinel structure have not yet been solved. This collapse usually leads to poor rate performance and to evolution of a two-plateau voltage profile, both of which are undesirable for practical applications. 1 Recently the development of a novel layered oxide cathode material, Li 1.2 Cr 0.4 Mn 0.4 O 2 , was reported, showing high capacity and good cycling stability in lithium-ion cells. 2 The material belongs to the solid solution series Li 2ϩx Cr y Mn 2Ϫy O 4ϩ␦ first reported by Davidson et al.,3,4 corresponding to the formulation Li 3 CrMnO 5 using the notation given by Davidson et al. ͑in the present work we prefer to use the notation Li 1.2 Cr 0.4 Mn 0.4 O 2 because it relates better to the rock salt crystal structure, as discussed below͒. Davidson et al. have evaluated the solid solution range in Li 2ϩx Cr y Mn 2Ϫy O 4ϩ␦ from y ϭ 0.49 to y ϭ 1.46, and found that discharge capacity tends to increase with higher Cr/Mn ratio, up to 230 mAh/g. 3 Although lower Cr/Mn ratios gave lower capacities, high reversible capacities of up to 200 mAh/g were found in examples with a Cr/Mn ratio of around 1.0.The objective of the work reported here is to examine in greater detail the structure and electrochemistry of the Li 1.2 Cr 0.4 Mn 0.4 O 2 material. We are interested in this phase because the composition has shown high capacity and yet contains 50% of its transition metal content as Mn. During the first charge of this material, up to 270 mAh/g ͑corresponding to nearly 1 Li in Li 1.2 Cr 0.4 Mn 0.4 O 2 ͒ can be extracted. This is only possible if either side reactions occur or the average transition metal valence state in the charged cathode is higher than the expected tetravalent state. The work reported here uses a combination of X-ray diffraction, and X-ray absorption at the transition metal K and L edges, to investigate the crystal and electronic structure of Li 1.2 Cr 0.4 Mn 0.4 O 2 , as prepared and during the first charge-discharge cycle. X-ray diffraction ͑XRD͒ gives information about the long range o...

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The zirconates Ln(2)Zr(2)O(7) (Ln = lanthanoid) have been studied using a combination of Zr L-edge X-ray absorption near edge structure (XANES) and synchrotron X-ray and neutron powder diffraction methods. These studies demonstrate that as the size of the lanthanoid cation decreases, the local structure evolves smoothly from the ideal pyrochlore toward the defect fluorite rather than undergoing an abrupt transformation. The Zr L-edge spectrum is found to be extremely sensitive to changes in the local coordination environment and demonstrates an increase in local disorder across the pyrochlore oxides. The sensitivity of the XANES measurements enables us to identify the progressive nature of the transition that could not be detected using bulk diffraction techniques.

The complex metal oxide SrCo0.5Ru0.5O(3-δ) possesses a slightly distorted perovskite crystal structure. Its insulating nature infers a well-defined charge distribution, and the six-fold coordinated transition metals have the oxidation states +5 for ruthenium and +3 for cobalt as observed by X-ray spectroscopy. We have discovered that Co(3+) ion is purely high-spin at room temperature, which is unique for a Co(3+) in an octahedral oxygen surrounding. We attribute this to the crystal field interaction being weaker than the Hund's-rule exchange due to a relatively large mean Co-O distances of 1.98(2) Å, as obtained by EXAFS and X-ray diffraction experiments. A gradual high-to-low spin state transition is completed by applying high hydrostatic pressure of up to 40 GPa. Across this spin state transition, the Co Kβ emission spectra can be fully explained by a weighted sum of the high-spin and low-spin spectra. Thereby is the much debated intermediate spin state of Co(3+) absent in this material. These results allow us to draw an energy diagram depicting relative stabilities of the high-, intermediate-, and low-spin states as functions of the metal-oxygen bond length for a Co(3+) ion in an octahedral coordination.

The reversible redox transformations [(NO)(2)Fe(S(t)Bu)(2)](-) ⇌ [Fe(μ-S(t)Bu)(NO)(2)](2)(2-) ⇌ [Fe(μ-S(t)Bu)(NO)(2)](2)(-) ⇌ [Fe(μ-S(t)Bu)(NO)(2)](2) and [cation][(NO)(2)Fe(SEt)(2)] ⇌ [cation](2)[(NO)(2)Fe(SEt)(2)] (cation = K(+)-18-crown-6 ether) are demonstrated. The countercation of the {Fe(NO)(2)}(9) dinitrosyliron complexes (DNICs) functions to control the formation of the {Fe(NO)(2)}(10){Fe(NO)(2)}(10) dianionic reduced Roussin's red ester (RRE) [PPN](2)[Fe(μ-SR)(NO)(2)](2) or the {Fe(NO)(2)}(10) dianionic reduced monomeric DNIC [K(+)-18-crown-6 ether](2)[(NO)(2)Fe(SR)(2)] upon reduction of the {Fe(NO)(2)}(9) DNICs [cation][(NO)(2)Fe(SR)(2)] (cation = PPN(+), K(+)-18-crown-6 ether; R = alkyl). The binding preference of ligands [OPh](-)/[SR](-) toward the {Fe(NO)(2)}(10){Fe(NO)(2)}(10) motif of dianionic reduced RRE follows the ligand-displacement series [SR](-) > [OPh](-). Compared to the Fe K-edge preedge energy falling within the range of 7113.6-7113.8 eV for the dinuclear {Fe(NO)(2)}(9){Fe(NO)(2)}(9) DNICs and 7113.4-7113.8 eV for the mononuclear {Fe(NO)(2)}(9) DNICs, the {Fe(NO)(2)}(10) dianionic reduced monomeric DNICs and the {Fe(NO)(2)}(10){Fe(NO)(2)}(10) dianionic reduced RREs containing S/O/N-ligation modes display the characteristic preedge energy 7113.1-7113.3 eV, which may be adopted to probe the formation of the EPR-silent {Fe(NO)(2)}(10)-{Fe(NO)(2)}(10) dianionic reduced RREs and {Fe(NO)(2)}(10) dianionic reduced monomeric DNICs in biology. In addition to the characteristic Fe/S K-edge preedge energy, the IR ν(NO) spectra may also be adopted to characterize and discriminate [(NO)(2)Fe(μ-S(t)Bu)](2) [IR ν(NO) 1809 vw, 1778 s, 1753 s cm(-1) (KBr)], [Fe(μ-S(t)Bu)(NO)(2)](2)(-) [IR ν(NO) 1674 s, 1651 s cm(-1) (KBr)], [Fe(μ-S(t)Bu)(NO)(2)](2)(2-) [IR ν(NO) 1637 m, 1613 s, 1578 s, 1567 s cm(-1) (KBr)], and [K-18-crown-6 ether](2)[(NO)(2)Fe(SEt)(2)] [IR ν(NO) 1604 s, 1560 s cm(-1) (KBr)].