L. A. Perelyaeva

Structure, ionic conduction, and phase transformations in lithium titanate Li4Ti5O12

The spinel structure of lithium titanate Li4Ti5O12 is refined by the Rietveld full-profile analysis with the use of x-ray and neutron powder diffraction data. The distribution and coordinates of atoms are determined. The Li4Ti5O12 compound is studied at high temperatures by differential scanning calorimetry and Raman spectroscopy. The electrical conductivity is measured in the high-temperature range. It is shown that the Li4Ti5O12 compound with a spinel structure undergoes two successive order-disorder phase transitions due to different distributions of lithium atoms and cation vacancies (□, V) in a defect structure of the NaCl type: (Li)8a[Li0.33Ti1.67]16dO4 → [Li□]16c[Li1.33Ti1.67]16dO4 → [Li1.33□0.67]16c[Ti1.67□0.33]16dO4. The low-temperature diffusion of lithium predominantly occurs either through the mechanism ... → Li(8a) → V(16c) → V(8a) → ... in the spinel phase or through the mechanism ... → Li(16c) → V(8a) → V(16c) → ... in an intermediate phase. In the high-temperature phase, the lithium cations also migrate over 48f vacancies: ... Li(16c) → V(8a, 48f) → V(16c) → ....

Crystal structure and optical properties of germanates Ln2Ca(GeO3)4 (Ln = Gd, Ho, Er, Yb, Y)

This paper reports on the results of structural and optical investigations of a new class of layered compounds Ln2Ga(GeO3)4 (Ln = Gd, Ho, Er, Yb, Y), which are promising for the use in photonics as converters of laser radiation.

Synthesis, optical properties, and photocatalytic activity of lanthanide-doped anatase

Quasi-one-dimensional (1D) Ti1 − xLnxO2 − x/2 anatase solid solutions were prepared by heating Ti1 − xLnx(OCH2CH2O)2 − x/2 precursors, where Ln = Nd, Eu, Tb, Er (x = 0.025), or Sm (0.005 ≤ x ≤ 0.025), in air. These solid solution were found to have a photocatalytic activity in hydroquinone oxidation in aqueous solution under exposure to UV radiation. UV-Vis absorption spectra were recorded for Ti1 − xLnxO2 − x/2 (Nd, Sm, Eu, Tb, or Er). The electronic structure and optical absorption spectra were calculated for anatase doped with neodymium, samarium, or terbium.

Electronic band structure, optical absorption, and photocatalytic activity of iron-doped anatase

Quasi-one-dimensional solid solutions of the composition Ti1 − xFexO2 − x/2 (0.005 ≤ x ≤ 0.050) with the anatase-type structure and extended aggregates have been prepared by the precursor method. The absorption spectra of the solid solutions have been investigated in the ultraviolet and visible regions, and the photocatalytic activity in the oxidation reaction of hydroquinone in water has been estimated. It has been found that the synthesized solid solutions serve as photocatalysts only under ultraviolet irradiation, and their photoactivity increases with an increase in the dopant concentration. The first-principles calculations of the electronic band structure and optical absorption in iron-doped anatase and rutile have been performed using the pseudopotential method LSDA + U (with the VASP software package). The on-site exchange-correlation parameters have been calibrated in the calculations of the electronic band structure of hematite α-Fe2O3 and ilmenite FeTiO3. It has been shown that, despite the appearance of impurity states within the band gap of anatase and rutile, doping with iron does not cause substantial absorption in the visible region, which correlates with the increase in photocatalytic activity only under ultraviolet irradiation. The most probable cause of the experimentally observed absorption in the visible region is the presence of finely dispersed hematite impurities in the obtained samples.

High-temperature Raman spectroscopy and phase transformations in phosphates and vanadates Ca3 − 3xNd2x(AO4)2 (A = P, V; 0 ≤ x ≤ 0.14)

The phases of variable composition Ca3 − 3xNd2x(AO4)2 (A = P, V; 0 ≤ x ≤ 0.14) based on calcium orthophosphate or orthovanadate are studied by Raman spectroscopy. The influence of the composition and temperature on the structural features of these compounds is considered. The changes observed in the Raman spectra at high temperatures are associated with the reversible phase transition due to the redistribution of calcium over different positions and partial reorientation of the AO4 tetrahedra.

Synthesis, structure, and properties of V2O3(XO4)2 (X = S, Se)

Compounds described as V2O3(XO4)2, where X = S or Se, were prepared from vanadium(V) oxide mixtures with concentrated sulfuric and selenic acids. The physicochemical properties of the products were studied; for V2O3(SeO4)2, the crystal structure was determined by powder X-ray diffraction and neutron diffraction, and its key differences from the structure of V2O3(SO4)2 were identified. V2O3(SeO4)2 crystallizes in the monoclinic system with the unit cell parameters a = 15.3831(2)Å, b = 5.54096(5)Å, c = 9.71644(7)Å, β = 111.886(1)°, V = 768.51Å3, space group C2/c (no. 15).

Synthesis and vibrational spectra of solid solutions based on lanthanum gallate

The synthesis conditions for single-phase solid solutions based on lanthanum gallate, LaGa1 − xMgxO3 − δ(x= 0–0.25, solid-phase method) and La1 − ySryGa1 − yMgyO3 − δ(y= 0–0.2, glycine nitrate method), have been investigated. The structural parameters have been calculated using X-ray powder diffraction data. The IR and Raman spectra have been analyzed. Regularities in the changes in the structural parameters and vibrational spectra with composition are established.

Electronic band structure and optical absorption of nanotubular zinc oxide doped with Iron, Cobalt, or Copper

The absorption spectra of the precursor-derived solid solutions Zn1 − xMxO (M = Fe, Co, Cu) with a tubular morphology of aggregates have been investigated in the ultraviolet and visible regions. The maximum metal concentration x in the Zn1 − xMxO solid solutions is 0.075 for iron, 0.2 for cobalt, and 0.1 for copper. It has been found that the optical absorption and the band gap of the Zn1 − xMxO compounds depend on the type of dopant. The obtained experimental data have been interpreted using the results of the performed ab initio calculations of the electronic band structure and optical absorption.

Synthesis and physicochemical study of M4Na2V10O28 · 10H2O (M=K, Rb, NH4)

AbstractThe formation conditions and physicochemical properties of binary decavanadates M4Na2V10O28 · 10H2O (M=K, Rb, NH4), synthesized by crystallization from saturated solutions of the NaVO3-MH2AsO4-H2O systems, were studied by chemical analysis, X-ray powder diffraction, microscopy, thermogravimetry, and IR spectroscopy. To optimize the synthesis conditions of M4Na2V10O28 · 10H2O, the ( 1-x)NaVO3 · 2H2O · xMH2AsO4-H2O (0.2 ≤ x ≤ 0.8) isomolar series method was applied to studying the interaction in the NaVO3-MH2AsO4-H2O systems (M = K, Rb, Cs) at the 0.4 mol/L total molar concentration of NaVO3 and MH2AsO4 in solutions. The studied M4Na2V10O28 · 10H2O compounds were shown to be isostructural with triclinic crystals (Z= 1, space group P