Irina G. Maslennikova

Structure and Internal Mobility of Complex Ions in Ammonium Pentafluorotitanate According to XRD and NMR Data

The crystal structure of NH4TiF5 (I) was determined (monoclinic crystals, a = 14.683(1), b = 6.392(1), c = 20.821(2) Å, β = 110.538(2); space group P21/n, Z = 4). Structure I is built from infinite zigzag chains of TiF6 octahedra linked by their cis-vertices in the [101] direction; the chains are connected by the ammonium ions forming hydrogen bonds. The chains of octahedra with the surrounding ammonium ions are staggered in the crystal lattice of I. 19F and 1H NMR spectroscopy was used to study the dynamics of the complex ions in NH4TiF5 in the temperature range 270-530 K. Types of ionic motion in the fluoride and proton subsystems were determined, and activation energies evaluated.

VOLATILE AMMONIUM FLUOROTITANATE

Single crystals of NH4TiO x F5−2x (x = 0.4) have been synthesized by gaseous product condensation at 300–400°C during the thermal decomposition of crystalline (NH4)2 Ti(OH) x F6−x (x = 0.6). The compound consists of kinked parallel infinite chains of cis-corner-connected TiF6 octahedra along the [1 0 1]-direction separated from each other by NH4 +-ions. The crystal parameters of this compound are as follows: monoclinic P21/n, a = 14.683 (1), b = 6.392 (1), c = 20.821 (2) Å, β = 110.538 (2)°, V = 1829.9 (3) Å3, Z = 16. The presence of oxygen was proved by chemical analyses, IR and NMR spectroscopy. Oxygen atoms must be randomly distributed in the crystal lattice. Fluorine and ammonium diffusion above 480 K can be the evidence of high ionic conductivity of this complex.

Nucleation and crystallization behavior of RE - doped tellurite glasses

The microstructure and crystallization of the glasses with composition (100-x-y)TeO2-xPbOP2O5-yPbF2:zMF3 (M= Er, Eu, Nd; x=42.5-30, y=5-30, z=0.5-3.0) were investigated by transmission electron microscopy (TEM) and luminescence methods. It was found that the doping with the rare-earth (III) fluorides promoted nucleation in the bulk glasses. The sizes of generated particles are about 2-5 nanometers and their shapes are close to spherical. The growth rate of crystallites depended on the lead fluoride content and glass forming rate. The heat treatment of the samples promotes the glass ceramic formation, where the crystalline phase is Pb2P2O7.

Bonding and structure of oxofluoroniobate-based glasses.

Glasses based on the oxofluoroniobate anion have been characterized by vibrational and solid-state NMR spectroscopy. The mechanism of glass formation in the systems K2NbOF5-MF3 (M = Al, In) has been suggested. A glass network is built from the chains of corner-sharing octahedra through -Nb-F(O)-M- and -Nb-F-Nb- bridges. Isolated NbOF5(2-) octahedra are also present, which is consistent with the glass composition. The high ionic mobility of NbOF5(2-) due to its fast reorientations results in equalization of the Nb-O and Nb-F distances, which is reflected in the appearance of the IR band at 700-800 cm(-1) not observed in the Raman spectrum. Its assignment to bridging -Nb-O-Nb- species accepted in the literature was not proven.