Glass formation and the phase diagram of crystalline components in the Sb<Subscript>2</Subscript>S<Subscript>3</Subscript>-PbI<Subscript>2</Subscript> system

Glasses in the Sb₂S₃-PbI₂ system are synthesized, and their physicochemical properties are investigated. The glasses possess high refractive indices (up to 3 or greater). The phase diagram of the Sb₂S₃-PbI₂ system is constructed from the data of differential thermal and X-ray powder diffraction analyses. The diagram exhibits an eutectic behavior. The eutectic is located at a content of 47 mol % PbI₂ and at a temperature of 370 ± 5°C.Original Russian Text Copyright © 2004 by Fizika i Khimiya Stekla, Samoilenko, Mohammad Arif, Novikov, Filatov, Blinov.     

Influence of composition and temperature on the band gap of glassy melts As<Subscript>2</Subscript>S<Subscript>3</Subscript>-Sb<Subscript>2</Subscript>S<Subscript>3</Subscript>

The edge absorption of glassy melts of the As-Sb-S system are investigated in the temperature interval 77–300 K. It is shown that the temperature dependence of the fundamental absorption edge is described by an exponential function of the photon energy. The temperature and concentration dependences of the optical band gap of glasses of the (As₂S₃)_{100 − x} · (Sb₂S₃) _x section are found. The known Varshni relation is used to describe the temperature dependence.     

Phase Equilibria in the Gd<Subscript>2</Subscript>O<Subscript>3</Subscript>-SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript> System

The phase equilibria are investigated and the phase diagram is constructed for the Gd₂O₃-SrAl₂O₄ pseudobinary join of the Gd₂O₃-SrO-Al₂O₃ ternary oxide system. One ternary compound, namely, Gd₂SrAl₂O₇, is revealed in the Gd₂O₃-SrAl₂O₄ join. It is found that this compound undergoes congruent melting.     

Phase equilibria in the Ho<Subscript>2</Subscript>O<Subscript>3</Subscript>-SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript> system

The phase formation is investigated and the phase diagram of the Ho₂O₃-SrAl₂O₄ system is constructed. A ternary compound, namely, Ho₂SrAl₂O₇, is revealed. It is established that this compound undergoes incongruent melting.     

Thermoelectric properties of Cu-dispersed bi<Subscript>0.5</Subscript>sb<Subscript>1.5</Subscript>te<Subscript>3</Subscript>

A novel and simple approach was used to disperse Cu nanoparticles uniformly in the Bi_0.5Sb_1.5Te₃ matrix, and the thermoelectric properties were evaluated for the Cu-dispersed Bi_0.5Sb_1.5Te₃. Polycrystalline Bi_0.5Sb_1.5Te₃ powder prepared by encapsulated melting and grinding was dry-mixed with Cu(OAc)₂ powder. After Cu(OAc)₂ decomposition, the Cu-dispersed Bi_0.5Sb_1.5Te₃ was hot-pressed. Cu nanoparticles were well-dispersed in the Bi_0.5Sb_1.5Te₃ matrix and acted as effective phonon scattering centers. The electrical conductivity increased systematically with increasing level of Cu nanoparticle dispersion. All specimens had a positive Seebeck coefficient, which confirmed that the electrical charge was transported mainly by holes. The thermoelectric figure of merit was enhanced remarkably over a wide temperature range of 323-523 K.     

Phase equilibria in the LaAlO<Subscript>3</Subscript>-LaSrAlO<Subscript>4</Subscript> system

The phase equilibria are investigated and the phase diagram is constructed for the LaAlO₃-LaSrAlO₄ pseudobinary join of the La₂O₃-SrO-Al₂O₃ ternary oxide system. One ternary compound, namely, La₂SrAl₂O₇, is found in the LaAlO₃-LaSrAlO₄ join. The crystallographic, thermal, and some other physicochemical characteristics of the compounds are reported.Original Russian Text Copyright © 2004 by Fizika i Khimiya Stekla, Popova, Tugova, Zvereva, Gusarov.     

Physicochemical and optical properties of glasses in the Ga<Subscript>4</Subscript>Ge<Subscript>21</Subscript>Se<Subscript>50</Subscript>-Sb<Subscript>2</Subscript>Se<Subscript>3</Subscript> system

This paper reports on the results of an investigation into the concentration behavior of the glass-forming ability, heat resistance, glass transition temperature, density, refractive index, transparent spectral region, and impurity optical absorption of glasses in the Ga₄Ge₂₁Se₅₀-Sb₂Se₃ system. The data obtained indicate that glasses in the Ga₄Ge₂₁Se₅₀-Sb₂Se₃ system with a high Sb₂Se₃ content are of interest as materials for use in fiber optics.     

Effect of PbTe on Thermoelectric Properties of Co<Subscript>0.88</Subscript>Ni<Subscript>0.12</Subscript>Sb<Subscript>2.91</Subscript>Sn<Subscript>0.09</Subscript>

The Co_0.88Ni_0.12Sb_2.91Sn_0.09 compound was synthesized by a metallurgical route, and PbTe powder was prepared by the low-temperature aqueous chemical method. Composite materials (xPbTe/Co_0.88Ni_0.12Sb_2.91Sn_0.09) were prepared by the ball-milling and the hot-pressed process. Electrical conductivities of xPbTe/Co_0.88Ni_0.12Sb_2.91Sn_0.09 hot-pressed samples decrease with increase of PbTe content, but their thermal conductivities were effectively improved due to induction of disperse phase. Due to agglomeration of the disperse phase, little thermal conductivity improvement occurs for composite material with low PbTe content. The ZT values of xPbTe/Co_0.88Ni_0.12Sb_2.91Sn_0.09 samples were hardly enhanced due to the negative contribution of electrical conductivity.     

Photoreduction of CO<Subscript>2</Subscript> into CH<Subscript>4</Subscript> using Bi<Subscript>2</Subscript>S<Subscript>3</Subscript>-TiO<Subscript>2</Subscript> double-layered dense films

Nano-sized bismuth sulfide (Bi₂S₃) and titanium dioxide (TiO₂) with the orthorhombic and anatase tetragonal structures, respectively, were synthesized for application as catalysts for the reduction of carbon dioxide (CO₂) to methane (CH₄). Four double-layered dense films were fabricated with different coating sequences—TiO₂ (bottom layer)/Bi₂S₃ (top layer), Bi₂S₃/TiO₂, TiO₂/Bi₂S₃: TiO₂ (1 : 1) mix, and Bi₂S₃: TiO₂ (1 : 1) mix/Bi₂S₃: TiO₂ (1 : 1) mix—and applied to the photoreduction of CO₂ to CH₄; the catalytic activity of the fabricated films was compared to that of the pure TiO₂/TiO₂ and Bi₂S₃/Bi₂S₃ doubled-layered films. The TiO₂/Bi₂S₃ double-layered film exhibited superior photocatalytic behavior, and higher CH₄ production was obtained with the TiO₂/Bi₂S₃ double-layered film than with the other films. A model of the mechanism underlying the enhanced photoactivity of the TiO₂/Bi₂S₃ double-layered film was proposed, and it was attributed in effective charge separation.     

A study on the synthesis of water-soluble Sb<Subscript>2</Subscript>S<Subscript>3</Subscript>

Water-soluble Sb₂S₃ sub-microspheres were synthesized by aqueous-phase arrested precipitation using mercaptoacetic acid as capping agent and thioacetamide (TAA) as sulfur source. The effects of the experimental conditions, such as temperature, sulfur source, reactants concentration and reaction time, on the shapes, structures and properties of the products were studied. FESEM, TEM showed the products have uniform size distribution. In addition, ultraviolet-visible spectrophotometry (UV-vis) and photoluminescence (PL) showed the resulting products have excellent optical properties.     

Crystallization of glasses in the SrO-B<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The crystallization of strontium borate glasses containing 16.7–43.0 mol % SrO is investigated. New crystalline compounds of the hypothetical compositions 2SrO · 3B₂O₃ (metastable) and SrO · 5B₂O₃ (stable below 750°C), as well as the metastable diborate modification β-SrO · 2B₂O₃, are revealed, and their X-ray powder diffraction data are obtained. It is demonstrated that, with a deficit of strontium oxide, the 4SrO · 7B₂O₃ compound forms solid solutions. Strontium triborate SrO · 3B₂O₃, which was previously prepared only through the dehydration of crystal hydrates, is produced using crystallization of glasses. The thermal stability of this compound is studied. The influence of the dispersity on the stability of different crystalline phases is discussed. Variants of the phase diagram for the SrO · B₂O₃-B₂O₃ system in the case of monolithic and dispersed samples are proposed from analyzing the experimental results and the data available in the literature.     

Raman spectra and surface structure of CaO-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> glass leached in potassium hydroxide solutions

It is difficult to research on the surface structure of amorphous phase in fly ash during leaching reaction due to crystalline phase and complex structure. In the present work, in order to reveal the effects of leaching reaction on the surface structure of amorphous phase in fly ash, the modelling CaO-Fe₂O₃-Al₂O₃-SiO₂ glass was prepared by the traditional melting methods. The leaching reaction of CaO-Fe₂O₃-Al₂O₃-SiO₂ glass with 7.5 M KOH was investigated by spectroscopy, spectrophotometer and wet chemical method. The results show that the content of Q ¹, Q ², Q ³ and Q ⁴ of glass without corrosion was 4.21, 9.51, 23.03 and 52.55%, respectively, which shows that the network polymerization of glass is compact. The leaching reaction of glass can be described by the following equation: dS/dt = k/(r + S ₀). Leaching in KOH for various times induces the content of Q ⁴ and Q ¹ to be decreased, and Q ² and Q ³ increased, resulted in the depolymerization of network and the surface glass dissolved in alkaline solution to form a gel phase. In stage one of leaching reaction, the rate of iron ion leached from glass surface was slow, which resulted in the small slope of straight-line relationship of leaching curve. In the following stage, the leaching rate of iron ion increased with the prolongation of time.     

Wetting,surface tension,and work of adhesion of As<Subscript>2</Subscript>S<Subscript>3</Subscript> and As<Subscript>2</Subscript>Se<Subscript>3</Subscript> glass melts to quartz glass

The contact angles of the quartz glass surface by the As₂S₃ and As₂Se₃ glass melts and surface tension of these glass melts in the temperature range of 325–370°С have been experimentally measured. The polytherms are linear and possess negative slope in the mentioned temperature range. The work of the adhesion of As₂S₃ and As₂Se₃ glass melts to the quartz glass surface has been calculated and compared to the data on the adhesion strength of the As₂S₃–SiO₂ and As₂Se₃–SiO₂ boundaries of the solid phases.     

Electrolytic properties of sulfide-conducting phases based on the BaLn<Subscript>2</Subscript>S<Subscript>4</Subscript> and CaLn<Subscript>2</Subscript>S<Subscript>4</Subscript> compounds of different structural types

The criteria for the choice of objects of investigation that possess sulfide-ion conduction, have the general formula MeLn₂S₄, and crystallize in different structural types are considered. The data obtained on the electrolytic properties of phases based on BaLn₂S₄(Ln = Nd, Sm, Tm); CaFe₂O₄ structural type), CaLn₂S₄(Ln = Y, Yb); Yb₃S₄ structural type), and CaLn₂S₄(Ln = Pr, Nd, Gd); Th₃P₄ structural type) are generalized. The performed comparative analysis of the properties of the synthesized electrolytes has demonstrated that the properties of solid electrolytes depend on the configuration of the f state of lanthanides to a greater extent than on the structure of the electrolytes under investigation. The vacancy mechanism of defects formation and sulfide-ion transfer in phases based on thiolanthanates is proposed reasoning from the data on the dependence of the electrolytic and thermodynamic properties on the composition.     

Kinetics of crystal nucleation of Na<Subscript>2</Subscript>O · 2CaO · 3SiO<Subscript>2</Subscript>-based solid solutions in glasses of the Na<Subscript>2</Subscript>SiO<Subscript>3</Subscript>—CaSiO<Subscript>3</Subscript> pseudobinary join

The kinetics of crystal nucleation is investigated in sodium calcium silicate glasses of two compositions (22.4 and 24.4 mol % Na₂O), which belong to the Na₂SiO₃—CaSiO₃ pseudobinary join and, according to the phase diagram, lie in the region of the formation of solid solutions between the compositions Na₂O · 2CaO · 3SiO₂ and Na₂O · CaO · 2SiO₂. The stationary rate of crystal nucleation of Na₂O · 2CaO · 3SiO₂-based solid solutions is measured as a function of temperature. It is shown that the maximum stationary rate of nucleation increases with an increase in the sodium oxide content in the initial glasses. The experimental data are analyzed in the framework of the classical nucleation theory.Original Russian Text Copyright © 2004 by Fizika i Khimiya Stekla, Soboleva, Yuritsyn, Ugolkov.     

Thermoelectric Properties of <Emphasis Type="Italic">x</Emphasis>PbTe/Yb<Subscript>0.2</Subscript>Co<Subscript>4</Subscript>Sb<Subscript>12</Subscript> Hot-Pressed Samples

The xPbTe/Yb_0.2Co₄Sb₁₂ compounds were prepared by the ball-milling and hot-pressed process. Electrical conductivity of the composite samples are reduced with a increase in PbTe content; and, their temperature dependence coefficients show the positive values. The maximum electrical conductivity of composite materials is ~80000 Sm⁻¹ at 800 K. The Seebeck coefficient (absolute value) of the composite material is obviously improved with an increase in the dispersed phase (PbTe) content; the Seebeck coefficient (absolute value) of the 10PbTe sample is ~260 μVK⁻¹ at 700 K, which increases by 13.6% relative to that of the Yb_0.2Co₄Sb₁₂ sample. The thermal conductivity of the composite samples is improved due to introduction of PbTe, and the thermal conductivity of the 10PbTe sample is ~3 Wm⁻¹ K⁻¹ at 550 K. The maximum value of ZT is 0.78 at 700 K for the 2.5PbTe sample.     

Thermodynamic modeling of the BaO-SiO<Subscript>2</Subscript> and SrO-SiO<Subscript>2</Subscript> binary melts

The evaluation of the thermodynamic properties and the phase diagrams for the binary BaO-SiO₂ and SrO-SiO₂ systems is carried out using a structural model for silicate melts and glasses. This thermodynamic model is based on the assumption that an addition of metal oxides to silica results in the depolymerization of the silicon-oxygen network, with a characteristic free energy change. A least squares optimization program permits all available thermodynamic and phase diagram data to be optimized simultaneously. In this manner, data for the above binary systems have been analysed and represented with a small number of parameters. The resulting equations represent the thermodynamic and phase diagram data for the alkaline-earth oxide-silica systems within error limits for most of the experimental data. In particular, the measured limiting liquidus slope, at X _{SiO 2} = 1, is well reproduced.     

A fragmentary model of vitreous As<Subscript>2</Subscript>S<Subscript>3</Subscript>

The X-ray scattering intensity curves for vitreous As₂S₃ are experimentally measured using soft (copper) and hard (molybdenum) X rays. The inclusion of all the specific features revealed in the experimental scattering intensity curves makes it possible to obtain the experimental atomic radial distribution function (ARDF) in the ordering range up to ～1 nm. The experimental ARDF is interpreted in the framework of the fragmentary model. A comparison of the experimental ARDF with the model ARDF calculated from the crystal structure data obtained for orpiment demonstrates that the corrugated layers inherent in crystalline As₂S₃ are retained in the glass structure but the characteristic interlayer interatomic distances are absent. The layers are joined together through the As₄S₅ molecular clusters. Microcrystals consisting of several unit cells are absent in the glass structure, which involves only the structural fragments of both crystalline analogs. One of the possible variants of their joining is proposed.     

Structure and crystallization of ZnO-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

Structure and crystalline behavior of the ternary system ZnO-B₂O₃-P₂O₅ glasses were investigated by means of X-ray diffraction (XRD) and infrared Raman spectra. The research showed that number of the planar [BO₃] units increases with the increase of B₂O₃ content. When the B₂O₃ content is above ≥10 mol %, the relative content of planar [BO₃] units increases rapidly and causes weakening of the glass structure and decrease in the chemical stability. In the crystallized glasses the predominant crystal phase Zn₂P₂O₇ decreases with the increase of B₂O₃ content, while the crystal phase BPO₄ increases with it, which cause the declining of chemical stability and the decrease of thermal coefficients of expansion.     

Preparation of sulfide ceramic materials based on BaSm<Subscript>2</Subscript>S<Subscript>4</Subscript>and CaGd<Subscript>2</Subscript>S<Subscript>4</Subscript> with the use of sol-gel and cryochemical technologies

Solid solutions in the MeLn₂S₄?x (mol %) MeS (Ln₂S₃) (Me = Ca, Ba; Ln = Sm, Gd) systems are prepared. The regions of solid solution formation are determined, the unit cell parameters of the crystal lattice are calculated, the total conductivity is investigated, and the activation energies for electrical conduction are calculated for samples with different prehistories. The electrolytic properties of phases based on calcium and barium thiolanthanates are studied, and the mechanism of defect formation is proposed.