The electrical conductivity of solid solutions with tetragonal syngony formed in 0.86(xKF - (1-x)PbF2) - 1.14SnF2 systems has been studied by 19F NMR and impedance spectroscopy. It was found that the Pb0.86Sn1.14F4 phase is characterized by better values of fluoride-ion conductivity than the ?-PbSnF4 compound. It was found that the substitution of Pb2+ ions by K+ up to ? = 0.07 in the structure of Pb0.86Sn1.14F4 contributes to increase in electrical conductivity by an order of magnitude relative to the original Pb0.86Sn1.14F4. The sample of the composition K0.03Pb0.83Sn1.14F3.97 has the highest electrical conductivity (?600 = 0.38 S cm-1, ?330 = 0.01 S cm-1). The fluoride anions in the synthesized samples of KxPb0.86-xSn1.14F4-x solid solutions occupy three structurally nonequivalent positions. It is shown that with increasing temperature, there is a redistribution of fluorine anions between positions in the anion lattice, which results in an increase in the concentration of highly mobile fluoride ions, which determine the electrical conductivity of samples.
The article presents the results of research on the hydrothermal synthesis of nanoscale oxide of cobalt and zirconium and their mixed oxide compositions. The synthesized samples have been characterized by the X‐ray phase, scanning electron microscopy and nitrogen adsorption‐desorption methods; the composition of the samples has been determined by chemical analysis methods, and their catalytic activity in the decomposition of hydrogen peroxide has been studied. It has been shown that during synthesis, highly dispersed cobalt and zirconium oxide are formed, and the sample of the composition (mol %): Co3O4(88)−ZrO2(12) has the highest specific surface area (181.2 m2/g) and the highest activity (K=6.18 ⋅ 10−2 s−1) against the decomposition of hydrogen peroxide. The increasing of the ZrO2 content in oxide compositions reduces their catalytic activity. The particle size in the synthesized samples is 7–38 nm.
In the PbF2 – SmF3 – SnF2 system, heterovalent substitution solid solutions Pb0.86-xSmxSn1,14F4+x (0 < x ≤ 0.15) with the structure β-PbSnF4 are formed. The unit cell parameters of solid solutions are satisfactorily described by Vegard’s rules. The electrical conductivity of the obtained samples decreases in the entire temperature range compared to Pb0.86Sn1.14F4 due to the introduction of SmF3 (at x≤0.08) in the initial structure. It brings them closer to the values of the electrical conductivity of β-PbSnF4. However, at temperatures above 520 K, the electrical conductivity of solid solutions is almost twice higher than that of the initial phase Pb0.86Sn1.14F4 (σ553 = 0.054 and 0.023 S/cm, respectively). The electrical conductivity of solid solutions increases with the Sm3+ content, reaching maximum values at x = 0.1. The Pb0.76Sm0.10Sn1.14F4.10 phases have the highest electrical conductivity and the lowest activation energy (σ373 = 1.08 • 10-2 S/cm). The substitution of Pb2+ ions by Sm3+ ions in the fluoride-conducting phase Pb0,86Sn1,14F4 helps to increase the electrical conductivity by almost an order of magnitude compared to the initial phase and by two orders of magnitude compared to β-PbSnF4. The ionic conductivity activation energy increases in the low-temperature region generally with increasing the SmF3 content and decreases proportionally at temperatures above 430 K. The nature of the dependence of the activation energy on the concentration of the heterovalent substituent and its value indicate that the conductivity of the obtained samples is provided by highly mobile interstitial fluoride ions in the structure of solid solutions. The Hebb-Wagner polarization saturation method was used to determine the electronic conductivity of the samples. It is 2 orders of magnitude lower than the ionic one. The fluorine ion transfer numbers are 0.99 and do not depend on the substituent content.
Cobalt and manganese oxides and their complex oxide compositions were obtained by the sol-gel method using various precipitators(ammonia solution and HMTA). It was determined by X-ray diffraction method that both individual and co-precipitated hydroxo compounds after calcination at 400 °С form oxide phases of Co3O4 and Mn3O4 composition. Samples obtained by sedimentation with ammonia solution have a larger specific surface area than synthesized in HMTA solution. When calcined at 400 °C, the specific surface area for cobalt-containing samples sedimentated with ammonia solution decreases, and for samples sedimentated from HMTA solution - increases. The pore volume depends on the precipitator and changes little during calcination. For co-sedimentated and calcined at 400 °C samples, the specific surface area plays a significant role: the higher it is, the greater the catalytic ability of the sample to decompose hydrogen peroxide. On the SEM image of samples driedat 100 °C, sedimentated with ammonia solution, agglomeration of flat particles of gitrated oxides of cobalt and/or manganese of globular form is observed. For samples deposited in HMTA solution, SEM images are represented by agglomeration of particles in the form of planar layers. Calcination at 400 °C partially destroys the structure. Kinetic studies of the decomposition of hydrogen peroxide with theparticipation of the obtained samples indicate the first order of the reaction. Samples of cobalt hydroxide and co-sedimentated cobalt and manganese hydroxy compounds synthesized in HMTA solution showed the best ability to catalyze. The highest productivity (dm3 H2O2 of decomposed 1 g of catalyst) is inherent in samples of cobalt hydroxy compounds and its composition with manganese compounds synthesized by HMTA, after heat treatment at 100 °C. The ability of such samples to catalytic decomposition of hydrogen peroxide is estimated to be not less than 2.4 dm3 H2O2 (14 days). Compared to compounds synthesizedwith ammonia solution, they retain their activity for a longer time.
The results of studies of the interaction of titanium dioxide with the eutectic melt of (0.48) NaCl–(0.52) CaCl2 (mol.) in the temperature range of 823–1073 K are shown. It is established that the interaction of titanium dioxide with the melt of sodium chlorides and calcium is accompanied by the formation in the salt phase of titanium compounds soluble in 1.0% solution of hydrochloric acid, and in the solid residue is recorded calcium titanate, and the number of products formed in both phases substantially. At temperatures above 923 K is formed calcium titanate, the relative amount of which increases with increasing temperature by reducing the equilibrium content of titanium compounds in the salt phase. At temperatures below 923 K, calcium titanate was not detected in the interaction products, and the content of titanium compounds in the salt phase was higher than at higher temperatures. The absence of calcium titanate in the solid residue after prolonged isothermal contact of TiO2 with the NaCl-CaCl2 melt in the temperature range 823–923 K may be due to the fact that at such temperatures, the dissolution of titanium dioxide occurs by physical mechanism or by a mixed physicochemical mechanism. The results of the calculations by the Schroeder-Le Chatelier equation support this. In the specified temperature range, the concentration of titanium compounds increases with temperature. Starting from 923 K the nature of the interaction between titanium dioxide and the melt changes. Apparently at such temperatures (923–1073 K), the contribution of the chemical interaction between the components accompanied by the formation of calcium metatanate and volatile titanium compounds is dominant. The quantitative content of the phase, which in composition in the solid residue is identified as CaTiO3, increases, and the number of titanium compounds in the salt phase (based on TiO2) decreases. The change of isobaric isothermal potential (∆G) in the temperature range of 300–1300 K of the exchange reactions between sodium chloride and calcium and titanium oxide is positive, so self-directed course is unlikely. The lowest Gibbs free energy values correspond to the reaction of the interaction of calcium chloride with titanium dioxide to form titanate or calcium oxide and tetrachloride or titanium oxochloride.
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