Ya. V. Baklanova

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.

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.

Influence of dispersion on the physicochemical properties of metatitanic acid

Li2TiO3 and H2TiO3 samples with various degrees of dispersion were investigated by X-ray diffraction, NMR spectroscopy, and electronic microscopy. It was shown that H2TiO3 has a distinct structure and exhibits high sorption activity in relation to rare earth elements. The sorption activity of H2TiO3 grows due to the increase in specific surface of samples.

Thermal Expansion and Luminescent Properties of Triorthogermanates CaLa 2- x Eu x Ge 3 O 10 ( x = 0.0–0.6)

Solid solutions CaLa2-xEuxGe3O10 (x = 0.0–0.6, Δx = 0.1) have been synthesized for the first time. The compounds are isostructural to CaLa2Ge3O10, they crystallize in the monoclinic system, space group P21/c, Z = 4. The low-temperature X-ray diffraction studies have revealed the strain anisotropy of germanate CaLa2Ge3O10 crystal lattice in the temperature range 80–298 K, and the linear thermal expansion coefficients have been calculated. The optical properties of the activated phases have been studied, and the influence of the dopant concentration and the excitation wavelength on the luminescence characteristics of the synthesized compounds has been established.

Novel IR Phosphor Based on Sr3La2(Ge3O9)2 : Nd3+,Ho3+ Germanate

Cyclogermanate Sr3La2(Ge3O9)2, isostructural to silicate Sr3Er2(Si3O9)2, activated by neodymium and holmium is obtained for the first time by the precursor method. Ion Nd3+ in the structure of Sr3La2(Ge3O9)2 is a sensitizer of the infrared luminescence of Ho3+. Excitation by radiation with a wavelength of 808 nm leads to a series of emission lines in the luminescence spectra of Sr3La2-xNdx(Ge3O9)2 : Ho3+ in the short-wave and middle-IR ranges (1.0–3.4 μm). The highest intensity of lines at 2.1 and 2.7 μm, associated with the 5I7 → 5I8 and 5I6 → 5I7 transitions in the Ho3+ ion, is found for compositions containing traces of holmium. Based on the analysis of the concentration dependences of the luminescence intensity, an optimal composition of the phosphor is determined, which ensures the maximum efficiency of conversion of laser radiation energy. The data obtained are interpreted in the assumption of cross-relaxation energy transfer from Nd3+ to Ho3+.

Influence of lattice defects on the reactivity of lithium titanate

Abstract7Li NMR spectroscopic experiments on Li2TiO3 demonstrate that the presence of planar crystal defects leads to lithium ion mobility in the temperature range of 30–100°C. Kinetics studies show the number of planar defects (and thus the rate of Li-H ion exchange) depends on the method and conditions of lithium titanate synthesis. The complete exchange of Li+ for H+ results in the formation of crystalline titanium oxyhydroxide TiO(OH)2 due to stabilization of defect state.