Inorganic Materials (v.50, #10)

Synthesis of a stable colloidal solution of PbS nanoparticles by S. I. Sadovnikov; Yu. V. Kuznetsova; A. A. Rempel (969-975).
A method has been proposed for the synthesis of stable colloidal solutions of lead sulfide nanoparticles from aqueous lead acetate and sodium sulfide solutions. The citrate ion and ethylenediaminetetraacetic acid were used as complexing agents to stabilize the solution. The solutions obtained were shown to remain stable at room temperature for at least 30 days from the instant of synthesis, depending on the initial reactant concentration. According to X-ray diffraction and dynamic light scattering data, the stability and coagulation of the nanoparticles in solution were influenced by the lead and sulfur concentration, the presence of complexing agents, and the quantitative relation between the lead and complexing agent ions in solution. Optical absorption measurements for the colloidal PbS nanoparticle solutions showed that their absorbance was a nonlinear function of reactant concentration.

Electrochemical, optical, and magnetic properties of Ni x InSe (0 < x ≤ 1) intercalation compounds by V. B. Boledzyuk; Z. D. Kovalyuk; M. N. Pyrlya; A. D. Shevchenko (976-980).
We have studied the electrochemical, optical, and magnetic properties of nickel-intercalated InSe single crystals. The energy position of the excitonic maximum and the full width at half maximum of the excitonic band in the Ni x InSe intercalation compounds have been shown to be nonmonotonic functions of nickel concentration. Nickel-intercalated InSe possesses ferromagnetic properties: the dependence of its magnetic moment on magnetic field has the form of a hysteresis loop, characteristic of hard-magnetic ferromagnets.

Phase equilibria in the pseudoternary system Ag2Se-Ag8GeSe6-Ag8SnSe6 by Z. M. Alieva; S. M. Bagkheri; I. J. Alverdiev; Yu. A. Yusibov; M. B. Babanly (981-986).
Phase equilibria in the Ag2Se-Ag8GeSe6-Ag8SnSe6 system have been studied by differential thermal analysis, X-ray diffraction, scanning electron microscopy, and emf measurements on concentration cells with Ag4RbI5 as a solid electrolyte. We have mapped out the T-x phase diagram of the constituent binary system Ag8GeSe6-Ag8SnSe6, those of two mutually perpendicular sections, and the liquidus projection. The two crystalline phases of the constituent selenides Ag8GeSe6 and Ag8SnSe6 have been shown to form a continuous series of solid solutions. The Ag2Se-Ag8GeSe6-Ag8SnSe6 system is a pseudoternary section through the quaternary system Ag-Ge-Sn-Se, and its phase diagram has a univariant eutectic.

The surface of Hg1 − xy Cd x Eu y Se crystals has been examined by electron microscopy using backscattered and secondary electron imaging, and the composition of the crystals has been determined. Using transport and optical measurements, we have identified the predominant electron scattering mechanisms in the Hg1 − xy Cd x Eu y Se crystals.

Ion-exchange iron sorption by carbon nanotubes and nanofibers by Son Tung Luu; Hoo Van Nguyen; E. G. Rakov (992-996).
We have studied room-temperature equilibrium in systems containing an aqueous Fe(II) or Fe(III) salt solution and carbon nanofibers or carbon nanotubes with various contents of functional groups. The sorption capacity of the sorbents has been determined as a function of contact time, sorbent weight to solution volume ratio, salt concentrations in solution, solution pH, and sorbent “solubility” (degree of functionalization). Equilibrium data have been described by the Langmuir and Freundlich equations, and the sorption kinetics have been represented by a first-order or pseudo-second-order equation. We have demonstrated that the sorption process can be accelerated by physical activation of the system.

Tubular alumina as a key component of new thermally stable ceramic materials by S. S. Berdonosov; N. B. Prosvetkin; Yu. V. Alekseeva; I. V. Melikhov (997-1002).
Using scanning electron microscopy and X-ray diffraction, we have examined processes that occur in tubular alumina during heating in air to temperatures in the range 1100–1200°C. The results demonstrate that, starting at temperatures between 600 and 700°C, α-Al2O3 (corundum) is formed in the solid material. Heating the tubular material to 1000°C converts some of the starting alumina into χ-Al2O3 and some into α-Al2O3. The samples calcined for 2–10 h at 1100°C contain α-Al2O3 and æ-Al2O3. Heating to 1000–1300°C has no effect on the shape of the tubular particles. The ceramics obtained in this way are stable in contact with water. When tubular alumina with a SiCl4 vapor hydrolysis product deposited on its surface is heat-treated at temperatures in the range 1100–1300°C, we observe the formation of mullite (Al2O3 · 2SiO2) on the surface of the tubular particles.

Conversion of short-wavelength electromagnetic radiation in SiO2 opal photonic crystals by V. S. Gorelik; L. S. Lepnev; A. O. Litvinova (1003-1006).
Reflection spectra of the (111) growth surface of opal photonic crystals differing in silica sphere diameter have been measured under illumination with narrowband ultraviolet and violet light from a laser and light-emitting diodes and with broadband light from a halogen lamp. We have found narrow strong bands differing in spectral position from the light from the short-wavelength excitation sources. The spectral position of these bands corresponds to that of photonic band gaps and is independent of excitation wavelength. The silica sphere diameter has no effect on the shape of the reflection band, and its position always correlates with that of the band gap of the opal. The present results demonstrate that exposure of a photonic crystal to short-wavelength radiation leads to conversion of the radiation to the spectral range of the band gap. The microscopic mechanism of the conversion process may involve three-photon parametric processes and amplification of the broadband photoluminescence due to structural defects in the silica matrix. Our results open up the possibility of creating new types of optically pumped solid gain media based on opal photonic crystals.

Reflection spectra of synthetic opal at liquid-nitrogen temperature by V. S. Gorelik; V. V. Filatov (1007-1011).
Reflection spectra of the (111) surface of synthetic opal crystals with sphere diameters of 210, 250, and 300 nm have been measured at room and liquid-nitrogen temperatures. At cryogenic temperatures, we observed a narrowing and shift of photonic band gaps due to liquid nitrogen infiltration into the opal pores. We have calculated ω(k) dispersion relations and determined the reflectivity of the opal surface. The results have been compared to the measured reflection spectra. We have detected photon conversion from the edges of the band gap to its center.

This paper analyzes phase states in the Na2O-WO3-MnO-Mn2O3 and Na2O-WO3-Mn2O3-SiO2 systems at temperatures of oxidative coupling of methane (OCM). The results indicate that, in the case of effective OCM, Na/W/Mn/SiO2 composite catalysts are in melt-Mn2O3 -tridymite (cristobalite) equilibrium.

Preparation of Ln2O2S (Ln = Gd, Dy, Y, Er, Lu) in flowing hydrogen and hydrogen sulfide by P. O. Andreev; E. I. Sal’nikova; I. M. Kovenskii (1018-1023).
The exposure of anhydrous Ln2(SO4)3 (Ln = Gd, Dy, Y, Er, Lu) sulfates to flowing hydrogen in the range 500–1050°C leads to the formation of Ln2O2S + Ln2O3 materials. With increasing reaction temperature, the mole fraction of Ln2O2S in the samples decreases. Single-phase Ln2O2S (Ln = Gd, Dy, Y, Er, Lu) compounds have been obtained by exposing the rare-earth sulfates first to flowing hydrogen in the range 500–600°C and then to hydrogen sulfide in the range 850–950°C.

Lanthanum oxide sulfurization in ammonium rhodanide vapor by A. V. Sotnikov; V. V. Bakovets; V. V. Sokolov; I. Yu. Filatova (1024-1029).
We have studied phase formation processes in the La-O-S system during La2O3 sulfurization in ammonium rhodanide vapor and identified the sequence of steps in lanthanum oxide conversion into oxysulfides and lanthanum sulfide using X-ray diffraction, IR absorption spectroscopy, and Raman spectroscopy. In the initial stage of the sulfurization process, we observed the formation of lanthanum dioxydisulfide, which converted into lanthanum dioxymonosulfide and lanthanum sesquisulfide during further sulfurization. Our results demonstrate that low structural perfection of lanthanum oxide allows reactive sulfur to penetrate the surface layer, which probably favors lanthanum dioxydisulfide formation.

Effect of the composition of starting yttrium aluminum hydroxide sols on the properties of yttrium aluminum garnet powders by S. S. Balabanov; E. M. Gavrishchuk; V. V. Drobotenko; A. D. Plekhovich; E. E. Rostokina (1030-1034).
A technique has been developed for the synthesis of yttrium aluminum garnet sols aggregationstable in water as a dispersion medium. Depending on the type of precursor used, the temperature of yttrium aluminum garnet formation varies from 900°C to 1100°C. We have obtained yttrium aluminum garnet nanopowders with an average particle size from 40 to 300 nm, depending on the aluminum yttrium hydroxide hydrosol synthesis procedure and annealing temperature.

Oxygen interstitial and vacancy conduction in symmetric Ln2 ± x Zr2 ± x O7 ± x/2 (Ln = Nd, Sm) solid solutions by A. V. Shlyakhtina; D. A. Belov; A. V. Knotko; I. V. Kolbanev; A. N. Streletskii; O. K. Karyagina; L. G. Shcherbakova (1035-1049).
We have compared (Ln2 − x Zr x )Zr2O7 + x/2 (Ln = Nd, Sm) pyrochlore-like solid solutions with interstitial oxide ion conduction and Ln2(Zr2 − x Ln x )O7 − δ (Ln = Nd, Sm) pyrochlore-like solid solutions with vacancy-mediated oxide ion conduction in the symmetric systems Nd2O3-ZrO2 (NdZrO) and Sm2O3-ZrO2 (SmZrO). We have studied their structure, microstructure, and transport properties and determined the excess oxygen content of the (Sm2 − x Zr x )Zr2O7 + x/2 (x = 0.2) material using thermal analysis and mass spectrometry in a reducing atmosphere (H2/Ar-He). The Ln2 ± x Zr2 ± x O7 ± x/2 (Ln = Nd, Sm) solid solutions have almost identical maximum oxygen vacancy and interstitial conductivities: (3–4) × 10−3 S/cm at 750°C. The lower oxygen vacancy conductivity of the Ln2(Zr2 − x Ln x )O7 − δ (Ln = Nd, Sm; 0 < x ≤ 0.3) solid solutions is due to the sharp decrease in it as a result of defect association processes, whereas the interstitial oxide ion conductivity of the (Ln2 − x Zr x )Zr2O7 + x/2 (Ln = Nd, Sm; 0.2 ≤ x < 0.48) pyrochlore-like solid solutions is essentially constant in a broad range of Ln2O3 concentrations.

Silicophosphate gels ranging widely in P2O5 content and specific surface area have been synthesized by a sol-gel process. We have demonstrated the possibility of producing medium-temperature high-conductivity systems based on silicophosphate matrices and CsH2PO4. The thermal, structural, and transport properties of composite proton electrolytes have been investigated. The results indicate that the electrical conductivity of the composites based on matrices with Si : P = 1 : 0.5 increases by up to three and half or four orders of magnitude and that their proton conductivity is ∼10−3 to 3 × 10−2 S/cm at temperatures from 90 to 220°C and a water vapor content of ≃0.6–1 mol % in air. The additive suppresses the superionic phase transition of CsH2PO4. The increase in conductivity at low contents of the heterogeneous component is due to both CsH2PO4 dispersion and the presence of protonated centers on the matrix surface. When the mole fraction of the additive exceeds 0.3, the composites contain CsH5(PO4)2, a compound with a lower thermal stability, which is responsible for their high conductivity in a limited temperature range.

We have demonstrated that silicophosphate matrices with various P2O5 contents can be used to produce medium-temperature highly conductive CsH2PO4-based composites. The low-temperature conductivity of all the composites studied is higher than that of the salt at low humidity by up to three and half to four orders of magnitude. The phase transition disappears with increasing additive content. The proton conductivity, thermal characteristics, and phase composition of the salt are shown to depend significantly not only on the composition of the composite but also on that of the silicophosphate matrix. The composites with Si : P = 1 : 0.14 contain disordered CsH2PO4 in the range x = 0.1–0.6. Increasing the percentage of the heterogeneous component leads to CsH2PO4 amorphization at x = 0.7 and the formation of the CsH5(PO4)2 compound at x = 0.8–0.9. The thermodynamic properties and thermal stability of the composites vary in accordance with this. We have assessed the thermal stability of the electrolytes of various compositions under isothermal conditions at 200–210°C and water vapor content of ≃0.6–1% in air in prolonged tests. The thermal stability of the materials is shown to depend significantly on both the percentage of the salt in the composite and the composition of the matrix. We have determined the optimal thermal and transport characteristics of the composites based on silicophosphate gel with lower phosphorus content. This opens up the possibility of using them as membranes in medium-temperature hydrogen fuel cells.

Lithium ion conductivity and mobility in the Li0.12Na0.88Ta0.4Nb0.6O3 solid solution by N. V. Sidorov; M. N. Palatnikov; N. A. Teplyakova (1063-1067).
Lithium ion mobility and the superionic phase transition in the Li0.12Na0.88Ta0.4Nb0.6O3 solid solution have been studied using temperature-dependent ionic conductivity measurements and Raman spectroscopy. From the temperature dependences of the conductivity and the width of a Raman line corresponding to Li+ and Na+ vibrations in the AO x (A = Na+, Li+) polyhedra, the average lifetime of the Li+ ion in its equilibrium position and the height of the barrier to hopping have been estimated at ≃3.9 × 10−13 s and ≃16 kJ/mol, respectively.

Phase equilibria and electrical properties of barium-containing relaxor-based solid solutions by M. V. Talanov; L. A. Shilkina; L. A. Reznichenko; S. I. Dudkina (1068-1074).
We have studied the effect of modification with Ba on the phase composition, structure, and electrical properties of ceramic samples of Pb(1−x)Bax(Mg1/3Nb2/3) m (Zn1/3Nb2/3) y (Ni1/3Nb2/3) n Ti z O3 (0 ≤ x ≤ 0.15) solid solutions and investigated phase equilibria in this system in the range 0 ≤ x ≤ 0.15. The results indicate that a tetragonal and a low-symmetry phase coexist in the composition range 0 ≤ x ≤ 0.05, a pseudocubic phase exists in the range 0.05 < x < 0.10, and a cubic phase exists in the range 0.1 ≤ x ≤ 0.15. We propose a scheme of solid-solution formation according to which partial barium substitution for lead in the range 0 ≤ x ≤ γ (where γ is structural nonstoichiometry) causes the Pb ions to leave distorted octahedra. For x > γ, Ba2+ substitutes for Pb2+ on the cuboctahedral site. The sintering temperature is shown to influence the phase composition of the modified ceramics. We demonstrate, that varying the Ba content of the solid solutions, one can obtain a series of materials with a wide range of electrical parameters (ɛ/ɛ0 = 2880–11000, K p = 0.07–0.43, and Q m = 48–8300) and potential applications in hydroacoustics, piezoelectric motors, and capacitor technology.