T. A. Denisova

Defect crystal structure of new TiO(OH)2 hydroxide and related lithium salt Li2TiO3

Crystal structures of TiO(OH)(2) and Li(2)TiO(3) have been studied in detail and refined using X-ray powder diffraction data. Both compounds possess a high concentration of defects in the structure. The crystal structure of the Li(2)TiO(3) salt obtained at 700 degrees C reveals stacking faults of LiTi(2) metal layers, which leads to the appearance of short-range order in three possible space groups: C2/c, C2/m, P3(1)12. The possibility to stabilise this imperfect state increases the mobility of the Li(+) ions in the structure and allows the complete exchange of lithium by hydrogen in acid water solutions with formation of TiO(OH)(2). The crystal structure of TiO(OH)(2) belongs to the layered double hydroxide structure type with the 3R(1) sequence of oxygen layers and can be described as a stacking of charge-neutral metal oxyhydroxide slabs [(OH)(2)OTi(2)O(OH)(2)]. TiO(OH)(2) is the first layered double hydroxide structure formed by a cation with oxidation state +4 only.

Electronic Structure and Chemical Bonding in Monoclinic and Cubic Li2-xHxTiO3 (0≤ x ≤ 2)

The linear “muffin‐tin” orbitals method in a tight binding approximation and extended Huckel theory are used to study the electronic structure and chemical bonding of lithium titanate (Li2TiO3) and its protonated analogs (Li1.75H0.25TiO3 and H2TiO3). The effect of protons on electron spectrum characteristics and bond strength are investigated for the monoclinic and cubic phases of lithium titanate. Phase stability is evaluated by cohesion energy calculations.

Nd3 +, Ho3 +-codoped garnet-related Li7La3Hf2O12 phosphor with NIR luminescence

Simultaneous emission lines around 1.05μm, 1.3μm, 1.8μm, 2.1μm and 2.7μm have been observed in Li7La3-xNdxHf2O12:Ho3+ (x=0.00-0.15) under 808nm laser diode excitation. Near-infrared luminescence due to holmium ions with residual concentration in the Li7La3Hf2O12 host has been studied. The intensity of 2.1 and 2.7μm lines associated with 5I7→5I8 and 5I6→5I7 transitions in Ho3+ depends on the neodymium codopant concentration. This result indicates that Nd3+ ions can be potentially used as sensitizers for Ho3+ ions to stimulate the intense near-infrared emission in this system. Possible energy transfer mechanisms between lanthanide ions have been briefly discussed.

Short CommunicationNd3 +, Ho3 +-codoped garnet-related Li7La3Hf2O12 phosphor with NIR luminescence

Simultaneous emission lines around 1.05μm, 1.3μm, 1.8μm, 2.1μm and 2.7μm have been observed in Li7La3-xNdxHf2O12:Ho3+ (x=0.00-0.15) under 808nm laser diode excitation. Near-infrared luminescence due to holmium ions with residual concentration in the Li7La3Hf2O12 host has been studied. The intensity of 2.1 and 2.7μm lines associated with 5I7→5I8 and 5I6→5I7 transitions in Ho3+ depends on the neodymium codopant concentration. This result indicates that Nd3+ ions can be potentially used as sensitizers for Ho3+ ions to stimulate the intense near-infrared emission in this system. Possible energy transfer mechanisms between lanthanide ions have been briefly discussed.

Charge distribution and mobility of lithium ions in Li2TiO3 from 6,7Li NMR data

A comparative analysis of 6,7Li NMR spectra is performed for the samples of monoclinic lithium titanate obtained at different synthesis temperatures. In the 7Li NMR spectra three lines are found, which differ in quadrupole splitting frequencies vQ and according to ab initio EFG calculations are assigned to three crystallographic sites of lithium: Li1 (vQ ∼ 27 kHz); Li2 (vQ ∼ 59 kHz); Li3 (vQ ∼ 6 kHz). The dynamics of lithium ions is studied in a wide temperature range from 300 K to 900 K. It is found that the narrowing of 7Li NMR spectra as a result of thermally activated diffusion of lithium ions in the low-temperature Li2TiO3 sample is observed at a higher temperature in comparison with a sample of high-temperature lithium titanate. Based on the analysis of 6Li NMR spectra it is assumed that there is mixed occupancy of lithium and titanium sites in the corresponding layers of the crystal structure of low-temperature lithium titanate, which hinders lithium ion transfer over regular crystallographic sites.

Structural, electronic properties and chemical bonding in protonated lithium metallates Li2−xHxMO3 (M = Ti, Zr, Sn)

Within density functional theory by an ab initio molecular dynamics method (SIESTA code) the features of structural, electronic properties and chemical bonding in lithium metallates Li2MO3 (M = Ti, Zr, Sn) are studied, as well as of their protonated forms Li2−xHxMO3 at all possible H+ → Li+ substitutions. With the use of the calculated crystal orbital overlap populations and the formation energies of Li2−xHxMO3 the most preferred H+ → Li+ substitutions in Li2MO3 metallates are discussed.

Proton state in hydrated fluoro-substituted brownmillerites Ba2In2O5–0.5yFy∙nН2О

Solid solutions Ba2In2O5–0.5yFy with the structure of brownmillerite are studied by IR and 1Н MAS NMR spectroscopy. During the fluorine doping, the nearest oxygen environment of indium atoms is distorted and a part of In–O bonds is shortened. It is shown that partial fluoride ion substitution for oxygen atoms results in an increase in the proton mobility in hydrated Ba2In2O5–0.5yFy∙nН2О phases.

Features of the local structure of hydrated fluorine-substituted solid solutions based on Ba2In2O5

It is found for hydrated solid solutions of Ba2−0.5xIn2O5−xFx · nH2O, Ba2In2O5−0.5yFy · nH2O (0 ≤ x ≤ 0.30; 0 ≤ y ≤ 0.24) that increasing the concentration of fluorine lowers the degree of hydration. The composition of proton-containing groups and the places of their localization in the structure of hydrated oxyfluorides are determined. The presence of fluorine in the complex oxide’s structure helps increase the mobility of protons.

Finely dispersed phases of MO(OH)2 (M = Zr, Hf) oxyhydroxides

We discuss studies of new finely dispersed phases of zirconium and hafnium oxyhydroxides MO(OH)2 (M = Zr, Hf) by means of X-ray diffraction, NMR, Raman scattering, IR spectroscopy, electronic microscopy and thermal analysis. It is demonstrated that these compounds and their precursors (lithium salts obtained by citrating) are isostructural. Hafnium oxyhydroxide is thermally more stable than its zirconium analog and decomposes at approximately 260°C.

Electronic structure and quadrupole interactions in triple molybdates Li2M3Al(MoO4)4, M = Cs, Rb

Within the density functional theory the electronic structure of triple molybdates Li2M3Al(MoO4)4, where M = Cs, Rb, is studied for the first time. It is found that all molybdates studied belong to wide band insulators with a band gap of ~4 eV. Quadrupole frequencies and asymmetry parameters of the electric field gradient near magnetic 7Li, 27Al, 87Rb, and 133Cs nuclei are calculated and experimental NMR spectra are interpreted.