D. G. Kellerman

Electronic structure, x-ray spectra, and magnetic properties of the LiCoO2−δ and NaxCoO2 nonstoichiometric oxides

This paper reports on a study of the magnetic susceptibility, x-ray photoelectron, and x-ray emission spectra of the LiCoO2−δ and NaxCoO2 nonstoichiometric oxides. The valence-band structure of LiCoO2 was analyzed. The hole concentration in the oxygen 2p band of LiNiO2 and LiCoO2 was derived from measurements of the O Kα emission spectra. Measurements of Co 2p and Co 3s photoelectron spectra showed that the Co3+ ions reside in the low-spin state with S=0. The deficiency of oxygen in the LiCoO2−δ reduced oxides gives rise to the formation of divalent cobalt ions. The deficiency of the alkali metal in NaxCoO2 initiates the formation of holes in the oxygen 2p band while not changing the electronic configuration d6 of the cobalt-ion ground state.

Semiconductor-metal transition in defect lithium cobaltite

The magnetic susceptibility, electrical conductivity, and x-ray photoelectron and x-ray absorption spectra of defect lithium cobaltites of the general formula Li1 − xCoO2 are investigated. It is found that, for lithium cobaltites with x > 0.25, the magnetic susceptibility increases abruptly and the conductivity type changes at T ∼ 150 K. The assumption is made that the semiconductor-metal transition in defect lithium cobaltite is caused by the increase in the diffusion mobility of lithium ions with an increase in the temperature when there is a correlation between spatial distributions of lithium vacancies and “electron” holes.

Optical absorption and nuclear magnetic resonance in lithium titanium spinel doped by chromium

The optical absorption and nuclear magnetic resonance spectra of Li4 − xCr3xTi5 − 2xO12 (x = 0, 0.01, 0.02, 0.04) solid solutions have been investigated. It has been found that, in the Li4Ti5O12 spinel, lithium ions migrate from tetrahedral to octahedral positions with increasing temperature. Doping of chromium to the spinel favors an increase in the fraction of tetrahedrally coordinated lithium and hinders diffusion.

Charge states of cobalt ions in nanostructured lithium cobaltite: X-ray absorption and photoelectron spectra

The charge states of ions in nanostructured lithium cobaltite prepared by severe plastic deformation under pressure have been determined using X-ray absorption spectroscopy and photoelectron spectroscopy, as well as calculations of the atomic multiplets with allowance for the charge transfer. It has been found that small deformations (pressures up to 5 GPa and angles of anvil rotation up to 30°) lead to the generation of lithium vacancies in the bulk of the nanostructured material and the formation of the Li2O phase on the surface. The charge compensation occurs at the expense of holes in oxygen 2p states; the electronic configuration of cobalt ions is 3d6L, where L is a hole in oxygen 2p states. It has been shown that nanostructured lithium cobaltite belongs to the class of insulators with a negative charge transfer energy. An increase in the degree of deformation of lithium cobaltite (at a pressure up to 8 GPa) leads to the formation of Co2+ ions (with the electronic configuration 3d7).

Magnetism of LiMn2O4 manganite in structurally ordered and disordered states

The specific features of the crystal structure and the magnetic state of stoichiometric lithium manganite in the structurally ordered Li[Mn2]O4 and disordered Li1 − δMnδ[Mn2 − δLiδ]O4 (δ = 1/6) states have been investigated using neutron diffraction, X-ray diffraction, and magnetic methods. The structurally disordered state of the manganite was achieved under irradiation by fast neutrons (Eeff ≥ 1 MeV) with a fluence of 2 × 1020 cm−2 at a temperature of 340 K. It has been demonstrated that, in the initial sample, the charge ordering of manganese ions of different valences arises at room temperature, which is accompanied by orthorhombic distortions of the cubic spinel structure, and the long-range antiferromagnetic order with the wave vector k = 2π/c(0, 0, 0.44) is observed at low temperatures. It has been established that the structural disordering leads to radical changes in the structural and magnetic states of the LiMn2O4 manganite. The charge ordering is destroyed, and the structure retains the cubic symmetry even at a temperature of 5 K. The antiferromagnetic type of ordering transforms into ferrimagnetic ordering with local spin deviations in the octahedral sublattice due to the appearance of intersublattice exchange interactions.

Magnetic properties of synthetic Ni3Si2O5(OH)4 nanotubes

The present study focuses on the magnetic properties of the nanotubular Ni3 Si2 O5 (OH)4 pecoraite, the structural analogue of chrysotile, obtained by hydrothermal synthesis. The cell parameters of the material, determined by X-ray diffraction, are , , and . The element analysis revealed the decrease of the Ni:Si ratio after hydrothermal treatment. The synthesized nanotubes have bigger outer and inner diameters in comparison to chrysotile. Using a vibration sample magnetometer, we determined the temperature of the ferromagnetic transition (23.7 K), of the ion in pecoraite and the blocking temperature (18 K).

X-ray spectra and specific features of the structure of lithium-sodium cobaltite LixNayCoO2

The electronic structure and specific features of the structure of nonstoichiometric cobaltite LixNayCoO2 (x = 0.42, y = 0.36) have been studied comprehensively. The calculated multiplet for the lowspin state of the Co3+ ion agrees with the experimental spectra. It has been established using X-ray absorption spectra measured in the total photoelectric effect yield and total fluorescence yield modes that the LixNayCoO2 cobaltite is stoichiometric with respect to the alkali metal near its surface and is defective inside. It has been demonstrated that the charge compensation in the case of an alkali metal deficit in LixNayCoO2 is due to holes in O 2p states.

Synthesis and Characterization of the LiMnP1–xVxO4–δ Solid Solutions

Compounds with the olivine-type structures are considered as perspective materials for lithium-ion power sources for both industrial and transport applications. Lithium iron phosphate is most highly developed from this family, but LiMnPO4 is supposed as much promising, due to its higher EMF vs. lithium. One of the main lacks of this class of materials is the low electronic conductivity. The traditional ways of conductivity increase by partial replacement of Mn with other transition metal for LiMnPO4 do not result to essential success. Our approach consisting in the influence onto anion sublattice results to better effect. Such solid solutions should be suitable for oxygen nonstoichiometry creation in virtue of ability of vanadium ion for oxidation degree downturn. Using magnetic methods, we succeeded to show that the required solid solutions are really formed. The optimal synthesis conditions of LiMnP1-xVxO4-δ solid solutions were determined. It was shown, that the doping of LiMnPO4 by vanadium jointly with oxygen nonstoichiometry brings to substantial enhance of electronic conductivity in this material. Observed peculiarities of the magnetic properties indicate the restructuring in the local environment in anion sublattice.

Cluster formation in LiNi0.4Fe0.6O2

AbstractThe structure of an LiNi0.4Fe0.6O2 cubic solid solution is determined using magnetic measurements and electron diffraction. It is found that this solid solution has a microinhomogeneous structure due to the formation of superparamagnetic clusters. The electron diffraction analysis of LiNi0.4Fe0.6O2 samples has revealed diffuse scattering characteristic of the substitutional short-range order in ordered solid solutions with a B1-type structure. It is shown that the short-range order is associated with the LiNiO2-type rhombohedral superstructure (space group