V. T. Kalinnikov

Preparation of LiTaO3 , LiNbO3 , and NaNbO3 from Peroxide Solutions

A procedure is described for preparing peroxide solutions of LiTaO3 and LiNbO3 . It is shown that the use of peroxide solutions makes it possible to obtain stoichiometric LiTaO3 , LiNbO3 , and NaNbO3 and LixNa1 – xNbО3 solid solutions.

Raman Spectra and Structural Perfection of Nominally Pure Lithium Niobate Crystals

We have studied the Raman spectra of nominally pure lithium niobate single crystals with congruent, near-stoichiometric, and stoichiometric compositions. The stoichiometric crystals have been grown by different procedures: from melts of congruent composition containing K2O (4.5 and 6 wt %) as an alkaline solvent (flux) and by a conventional procedure from a melt containing a considerable excess of Li2O (58.6 mol %). The results indicate that the growth procedure has a significant effect on the structural perfection and photorefractive properties of the crystals because it determines the nature and density of structural defects and, hence, the concentration of localized electrons. Stoichiometric crystals grown from a K2O flux, though less perfect than stoichiometric crystals grown by a conventional procedure, exhibit a reduced photorefractive effect in comparison with both stoichiometric crystals grown with no flux and crystals of congruent composition.

Sol-gel synthesis of Li1.3Al0.3Ti1.7(PO4)3 solid electrolyte

A modified sol-gel process was studied as applied to synthesize a lithium-conducting solid electrolyte of composition Li1.3Al0.3Ti1.7(PO4)3 (LATP) using water-soluble salts Al(NO3)3 · 9H2O, LiNO3 · 3H2O, and (NH4)2HPO4 and a titanium(IV) citrate complex. As-synthesized samples were characterized using X-ray powder diffraction, DSC/TG, SEM, and impedance spectroscopy. Sintering of as-synthesized amorphous powders at 700°C was found to yield LATP with crystallite sizes of 42–48 nm. Ionic conductivity of the electrolyte measured in the frequency range 25–106 Hz in disks having 86–90% density that were sintered at 1000°C was (3–4) × 10−4 S/cm. Temperature-dependent ionic conductivity was studied in the range 25–200°C. The activation energy of conduction was determined for LATP.

Investigation into the mechanism of interaction of calcium and magnesium silicates with carbon dioxide in the course of mechanical activation

A prolonged grinding of diopside, akermanite, sphene, wollastonite, and enstatite is accompanied by absorption of CO2 from the environment (carbonation) along with amorphization and hydration. The IR spectra of ground minerals contain bands of distorted carbonate groups due to absorption of carbon dioxide. If the mechanical activation is not attended by the distortion of the crystal lattice, the sorption of carbon dioxide results in the formation of undistorted [CO32–] groups.

Effects of nonstoichiometry and doping on the curie temperature and defect structure of lithium niobate

LiNbO3 crystals doped with Gd, Zn, Cu, and Er to various levels were grown by the Czochralski technique. The structural parameters, Curie temperature, and density of the LiNbO3 crystals were determined as a function of composition. With increasing Gd content, thea parameter of the hexagonal cell increases, c remains constant within the experimental error, density increases, and Tc gradually decreases. The defect structure and properties of LiNbO3 doped with Gd, Zn, Cu, Er, Mg, and Ta are contrasted with those of nominally undoped LiNbO3 crystals differing in Li/Nb ratio. The results suggest that the variation of the Curie temperature with composition is determined primarily by the position that the dopant cations occupy in the structure of lithium niobate.

Physical Chemistry of the Magnetic Semiconductor CdCr2Se4

The magnetic semiconductor CdCr2Se4 is the best known chalcogenide spinel. This article reviews the available information about this compound: phase diagrams, homogeneity region, vapor pressure, crystal growth, doping of crystals, and defect chemistry. A large body of data in this field have been obtained by the authors.

Synthesis, properties, and thermal decomposition of compounds [Co(En)3][Fe(CN)6] · 2H2O and [Co(En)3]4[Fe(CN)6]3 · 15H2O

Binary complex salts, [Co(En)3][Fe(CN)6] · 2H2O and [Co(En)3]4[Fe(CN)6]3 · 15H2O, are synthesized. The properties of the salts and their thermolysis in air, dihydrogen, and argon are studied. Oxides of the central ions of the binary complex salts are found to be the thermolysis products in an oxidative atmosphere. Solid solutions (intermetallic compounds) CoFe are the thermolysis products in the reductive atmosphere, whereas intermetallides containing considerable amounts of C and N and an impurity of Co and Fe oxides are the thermolysis products in an inert atmosphere. Gaseous thermolysis products in dihydrogen and argon are NH3, hydrocarbons, and ethylenediamine.

Stoichiometry and doping effects on cation ordering in LiNbO3 crystals

The cation disorder in stoichiometric and congruent lithium niobate crystals and also in congruent crystals doped with Y3+ or Gd3+ has been studied by X-ray diffraction and Raman scattering spectroscopy using vacancy models. The results indicate that the structural disordering induced by doping with Y3+, revealed by both X-ray diffraction and Raman spectroscopy, can be understood in terms of the mechanism of yttrium incorporation into the cation sublattice of the crystal. Yttrium substitution for Nb5+ on its normal lattice site causes Nb5+ to occupy vacant octahedra, thereby increasing the cation and vacancy disorder along the polar axis and distorting the octahedra because the ionic radius of Y3+ exceeds that of Nb5+.

Gelatin-containing calcium hydroxyapatites: Synthesis and physicochemical characterization

The CaCl2-(NH4-)2HPO4-NH3-H2O-gelatin system was studied at 25°C using the solubility (residual concentrations) method. Stoichiometric nanocrystalline (11–15.4 nm) gelatin-containing calcium hydroxyapatites (HAs) were found to form. They were characterized by chemical analysis, thermal analysis, Xray powder diffraction, and IR spectroscopy.

Magnesium-vapor reduction of niobium oxide compounds

The effect of precursor composition and reduction conditions on the characteristics of niobium powders obtained by magnesium reduction were studied. The hypothesis of the possible increase in the specific surface area of the powders by a large factor by using complex oxides as precursors was confirmed. With magnesium niobate Mg4Nb2O9 as the precursor, mesoporous powders, unprecedented in the world, with a specific surface area of up to150 m2 g–1 and an average pore size of 4.6 nm were produced.