CaGa<Subscript>2</Subscript>Se<Subscript>4</Subscript>–GaSe system

The phase relations in the CaGa₂S₄–GaSe system have been studied using differential thermal analysis, X-ray diffraction, microstructural analysis, microhardness tests, and density measurements, and its T–x phase diagram has been mapped out. The CaGa₂S₄–GaSe system has been shown to be a pseudobinary join of the ternary system Ca–Ga–Se. The CaGa₂S₄–GaSe system has been found to contain limited solid solutions based on the constituent selenides. The electrical conductivity of CaGa₂S₄ has been measured and its current–light behavior and photoelectric properties have been studied.     

Thermoelectric properties of tetradymite-like layered materials in the pseudoternary system Sb<Subscript>2</Subscript>Te<Subscript>3</Subscript>–GeTe–Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript>

The Hall coefficient, resistivity, and thermoelectric power of quaternary tetradymite-like layered materials in the pseudoternary system Sb₂Te₃–GeTe–Bi₂Te₃ have been measured in the temperature range 100–800 K. The results demonstrate that all of the samples studied in the Sb₂Te₃–GeTe–Bi₂Te₃ system are p-type and have high hole concentration due to point defects. Plots of lnσ against 1/T in the intrinsic region were used to evaluate the band gap (ΔE) of two materials: GeSb_3.91Bi_0.03Te_6.91(ΔE = 0.22 eV) and GeSbBiTe₄ (ΔE = 0.197 eV).     

Formation of Compounds in the Ag<Subscript>2</Subscript>O–Sb<Subscript>2</Subscript>O<Subscript>3</Subscript>–MoO<Subscript>3</Subscript> System on Heating

This paper presents a detailed study of phase formation processes in the AgNO₃–Sb₂O₃–MoO₃ system during heating in air. The compositions of the solid-state reaction products have been determined using thermogravimetry and qualitative X-ray diffraction. The results demonstrate that, at a final heat treatment temperature of 1023 K, synthesis yields a range of Ag_2–xSb_2–xMo _x O₆ compounds with the pyrochlore structure and 0.0 ≤ x ≤ 2.0. The structural parameters of the synthesized phases have been refined by the Rietveld method in space group Fd3?m and their electrical conductivity has been measured.     

Glasses formation,characterization, and crystal-structure determination in the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–Sb<Subscript>2</Subscript>O<Subscript>3</Subscript>–TeO<Subscript>2</Subscript> system prepared in an air

A glass-forming domain is found and studied within Bi₂O₃–Sb₂O₃–TeO₂ system. The glasses composition were obtained in pseudo-binary xSbO_1.5, (1−x)TeO₂ for 0.05 ≤ x ≤ 0.20. The constitution of glasses in the system Sb₂O₃–TeO₂ was investigated by DSC, Raman, and Infrared spectroscopy. The influence of a gradual addition of the modifier oxides on the coordination geometry of tellurium atoms has been elucidated based Infrared and Raman studies and showed the transition of TeO₄, TeO₃₊₁, and TeO₃ units with increasing Sb₂O₃ content. XRD results reveal the presence of three crystalline: γ-TeO₂, α-TeO₂, and SbTe₃O₈ phases during the crystallization process. The density of glasses has been measured. The investigation in the ternary system by the solid state reaction using XRD reveals the existence of a solid solution Bi_1−x Sb_1−x Te_2x O₄ isotopic to BiSbO₄ with 0 ≤ x ≤ 0.1.     

Syntheses and proton conductivity of mesoporous Nd<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> and NdOCl–SiO<Subscript>2</Subscript> composites

Two mesoporous oxide composites of Nd₂O₃–SiO₂ and NdOCl–SiO₂ were synthesized using SBA-15 as a template and neodymium nitrate or neodymium chloride as a precursor. The porous Nd₂O₃–SiO₂ with a SBA-15-like structure has amorphous walls and the porous NdOCl–SiO₂ with a replicated structure of SBA-15 has crystalline walls. These porous materials were characterized by X-ray diffraction, transmission electron microscopy and nitrogen adsorption/desorption. They exhibited significant proton conductivities in the presence of moisture at low temperatures and the highest conductivity observed was 4.55 × 10⁻⁴ S/cm at 47 °C in wet air (RH = 28.6%).     

Thermal and dielectric properties of the LTCC composites based on the eutectic system BaO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript>

The low-temperature co-fired ceramic (LTCC) composites containing quartz based on the eutectic system BaO–Al₂O₃–SiO₂–B₂O₃ are fabricated at the sintering temperature below 980 °C. Preparation process and sintering mechanism were described and discussed, respectively. The results indicated that the addition of quartz to the eutectic system can availably improve dielectric properties of the LTCC composites. In addition, The LTCC composites with optimum compositions, which were obtained by the regulation of an Al₂O₃ content in the composite, can express excellent dielectric properties (permittivity: 5.94, 5.48; loss: 7 × 10⁻⁴, 5 × 10⁻⁴), considerable CTE values (11.7 ppm. °C⁻¹, 10.6 ppm. °C⁻¹) and good mechanical properties (128 MPa,133 MPa).     

In vitro dissolution behavior of SiO<Subscript>2</Subscript>–MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–K<Subscript>2</Subscript>O–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–F glass–ceramic system

Herein, we report the results of the in vitro dissolution tests, which were carried out by immersing the selected glass-ceramic samples in artificial saliva (AS) for various time periods of up to 42 days. In our experiments, the SiO(2)-MgO-Al(2)O(3)-K(2)O-B(2)O(3)-F glass ceramics with different crystal morphology and crystal content were used and a comparison is also made with the baseline glass samples (without any crystals). The bioactivity of the samples was probed by measuring the changes in pH, ionic conductivity and ionic concentration of AS following in vitro dissolution experiments. High resistance of the selected glass-ceramic samples against in vitro leaching has been demonstrated by minimal weight loss (<1%) and insignificant density change, even after 6 weeks of dissolution in artificial saliva. While XRD analysis reveals the change in surface texture of the crystalline phase, FT-IR analysis weakly indicated the Ca-P compound formation on the leached surface. The experimental measurements further indicate that the leaching of F(-), Mg(2+) ions from the sample surface commonly causes the change in the surface chemistry. Furthermore, the presence of (Ca, P, O)-rich mineralized deposits on the leached glass-ceramic surface as well as the decrease in Ca(2+) ion concentrations in the leaching solutions (compared to that in the initial AS solution) provide evidences of the moderate bioactive or mild biomineralisation behaviour of investigated glass-ceramics.     

Optical properties and crystallization of glasses in the system Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–MoO<Subscript>3</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript>

The purpose of this work is to study the optical properties and crystallization of glasses in the ternary system Bi₂O₃–MoO₃–B₂O₃. In order to verify the obtaining of bismuth borate crystal phases several glass compositions have been selected for crystallization. The obtained samples were characterized by X-ray diffraction, scanning electron microscopy and UV–Vis spectroscopy. The UV–Vis spectroscopy showed that the obtained glasses are transparent in the visible region. The values of optical band gap (E _opt) and changes in cut-off (λ_c) depending on composition are reported. It was established that the increase in the MoO₃ content led to decreasing the transmittance of the glasses. Moreover, the absorption edge shifts towards longer wavelength.     

Vaporization in the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–MgO system

The pseudobinary system Al₂O₃–MgO has been studied in the temperature range 1750–2100 K by the Knudsen effusion method in combination with mass spectrometric analysis of the vapor phase. Over the entire composition range, except for the 100 mol % Al₂O₃ boundary, the vapor phase over the system consists of three species: Mg, O₂, and O. The partial pressures obtained have been used to construct a p–x section through the Al₂O₃–MgO phase diagram at 1900 K. The standard enthalpy of formation of the MgAl₂O₄ spinel at 298 K has been determined by third-law calculations:–2301.61 ± 11.00 kJ/mol. We have derived equations for the temperature dependences of the partial pressures of the vapor species over the Al₂O₃–MgO system.     

High-temperature heat capacity of the oxide compounds in the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–V<Subscript>2</Subscript>O<Subscript>5</Subscript> system

The compounds BiVO₄, Bi₄V₂O₁₁, and Bi₁₂V₂O₂₃ have been prepared by solid-state synthesis using stoichiometric mixtures of Bi₂O₃ and V₂O₅. The effect of temperature on the heat capacity of the synthesized bismuth vanadates has been studied by differential scanning calorimetry in the range 350–950 K. The C _p (T) curves have extrema at 531.7 K for BiVO₄ and at 725.2 and 852.8 K for Bi₄V₂O₁₁, which are due to polymorphic transformations of these compounds.     

Thermoelectric Properties of Layered Compounds and Multicomponent Solid Solutions in the Pseudoternary System Sb<Subscript>2</Subscript>Te<Subscript>3</Subscript>–PbTe–Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript>

The thermoelectric properties of layered compounds and solid solutions in the Sb₂Te₃–PbTe–Bi₂Te₃ system have been studied in a wide temperature range. The quaternary compounds and multicomponent solid solutions in this system have been shown to have a very low lattice thermal conductivity. The electrical conductivity of all the materials decreases with increasing temperature. All of the materials have been shown to be n-type. The layered compounds and multicomponent solid solutions have high thermoelectric efficiency, which makes them promising n-type thermoelectric materials.     

Compositional dependence of the structural and dielectric properties of Li<Subscript>2</Subscript>O–GeO<Subscript>2</Subscript>–ZnO–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

(10Li₂O–20GeO₂–30ZnO–(40-x)Bi₂O₃–xFe₂O₃ where x = 0.0, 3, 6, and 9 mol%) glasses were prepared. A number of studies, viz. density, differential thermal analysis, FT-IR spectra, DC and AC conductivities, and dielectric properties (constant ε′, loss tan δ, AC conductivity, σ _ac, over a wide range of frequency and temperature) of these glasses were carried out as a function of iron ion concentration. The analysis of the results indicate that, the density and molar volume decrease with an increasing of iron content indicates structural changes of the glass matrix. The glass transition temperature T _g and onset of crystallization temperature T _x increase with the variation of concentration of Fe₂O₃ referred to the growth in the network connectivity in this concentration range, while glass-forming ability parameter ΔT decrease with increase Fe₂O₃ content, indicates an increasing concentration of iron ions that take part in the network-modifying positions. The FT-IR spectra evidenced that the main structural units are BiO₃, BiO₆, ZnO₄, GeO₄, and GeO₆. The structural changes observed by varying the Fe₂O₃ content in these glasses and evidenced by FTIR investigation suggest that the iron ions play a network modifier role in these glasses while Bi₂O₃, GeO₂, and ZnO play the role of network formers. The temperature dependence of DC and AC conductivities at different frequencies was analyzed using Mott’s small polaron hopping model and, the high temperature activation energies have been estimated and discussed. The dielectric constant and dielectric loss increased with increase in temperature and Fe₂O₃ content.     

Sintering and microstructure of materials based on the fluorohydroxyapatite–ZrO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> system

We have studied the influence of the sintering temperature and modifying additives on the phase composition, microstructure, and mechanical strength of a fluorohydroxyapatite-based composite ceramic material containing 20 wt % zirconia. The addition of 5 wt % alumina has been shown to prevent recrystallization processes and contribute to phase composition stabilization. Moreover, the addition of a sintering aid (2 wt %) has made it possible to lower the sintering temperature to 1200°C and raise the bending strength of the material to 143 MPa.     

Characterization and analysis of CaO–SiO<Subscript>2</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript> ternary system ceramics

The dielectric, thermal and mechanical properties of CaO–SiO₂–B₂O₃ ternary system ceramics by solid-phase method have been carried out and quantitive analysis been examined by X-ray diffraction (XRD) patterns. The results showed that the major crystalline phase of CaO–SiO₂–B₂O₃ ternary system ceramics was wollastonite (about 90 wt%) which existed at the temperature ranging from 950 to 1,100 °C. It is also observed that wollastonite could be transformed to pseudowollastonite at 1,200 °C. In addition, with increase in calcination temperature, the amount of wollastonite increases. When the sintering temperature is at 1,100 °C, the amount of wollastonite has a maximum value of 92.7 wt%. Accordingly, CaO–SiO₂–B₂O₃ ternary system ceramics achieved excellent properties at 1,100 °C, such as dielectric constant of 8.38, dielectric loss of 1.51 × 10⁻³ at 1 MHz, linear thermal-expansion coefficient (300 K) of 6.68 × 10⁻⁶/K, bending strength of 121.75 Mpa. Analysis of the mechanical and dielectric properties showed that the measured bending strength, dielectric constant and loss of CaO–SiO₂–B₂O₃ ternary system ceramics can be substantially modified and improved by controlling the sintering temperature, in particular due to the amount of wollastonite crystalline phase and size of grains.     

Thermoelectric properties of Sb<Subscript>2</Subscript>Te<Subscript>3</Subscript>–Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> solid solutions prepared through melt solidification in liquids

Using scanning electron and optical microscopies, we have studied the morphology of fracture surfaces and microstructure of samples of an Sb₂Te₃–Bi₂Te₃ solid solution (p-type conductivity) prepared by hot pressing and extrusion of granules produced through melt solidification in liquids. All of the samples were found to contain an additional phase in the form of a tellurium-based eutectic, and their macroscopic structure was shown to depend on the granule comminution procedure. The electrical conductivity, Seebeck coefficient, and thermal conductivity of the samples have been measured in the range 100–700 K. We have obtained materials with the highest dimensionless thermoelectric figure of merit ZT ~ 1.0 at temperatures from 300 to 440 K.     

High-temperature laser coatings of the ZrB<Subscript>2</Subscript>–MoSi<Subscript>2</Subscript> system on graphite

Coatings of the ZrB₂–MoSi₂ system on graphite (≤ 50 μm thick and 14–15 GPa in hardness) have been produced by pulse laser melting in air of two-layer powder coating with sublayers based on ZrB₂ with additions of ZrSi₂ and SiC. Different coating structures: eutectics of the ZrSiO₄–SiO₂ system based on zircon or a structure of micron-thick fibers of composition Zr(Mo)B₂ are formed depending on the sublayer composition, which controls the coating heat conductivity and accordingly, the crystallization rate of the bath of melt. The prospects of this line of investigations are the improvement of a laser technology of the deposition of high-temperature coating using continuous wave lasers.     

Phase relations in the Cu<Subscript>2</Subscript>Te–Al<Subscript>2</Subscript>Te<Subscript>3</Subscript> semiconductor system

The T-x phase diagram of the Cu₂Te–Al₂Te₃ semiconductor system was achieved experimentally using 24 different mixtures of the binary compounds. The results of X-ray powder diffraction, differential thermal analysis, and electron microprobe analysis are presented. It was established that only one ternary compound CuAlTe₂ exists in this system crystallizing in the tetragonal structure of chalcopyrite with lattice constants at room temperature a = 6.035(5) and c = 11.94(1) Å. The maximal homogeneity region of this compound was discovered being limited by compositions with 0.474 and 0.544 molar part of Al₂Te₃ at 673 K. CuAlTe₂ decomposes peritectically at 1,183 K to (Cu₂Te)_0.97(Al₂Te₃)_0.03 alloy with the structure of Cu₂Te and liquid with the composition close to (Cu₂Te)_0.40(Al₂Te₃)_0.60 which transforms into homogeneous liquid region at 1,240 K.     

Crystallization and microstructural evolution of MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript>–La<Subscript>2</Subscript>O<Subscript>3</Subscript> glass-ceramics

Crystallization and microstructure of glasses with the molar compositions 1MgO·1.2Al₂O₃·2.8SiO₂·1.2TiO₂·xLa₂O₃ (x = 0.1 and 0.4) were thermally treated at different temperatures in the range from 950 to 1250 °C and then analyzed by X-ray diffraction and scanning electron microscopy, in combination with energy-dispersive X-ray spectroscopy and electron backscatter diffraction. It was found that the microstructure is first homogeneous with the precipitation of randomly distributed crystals and then indialite domains with embedded perrierite and rutile crystals are formed. For higher temperatures or prolonged times, more domains appear and expand into the bulk of the sample. Finally, the entire sample consists of the indialite domains and the boundaries that are enriched in rutile, perrierite, and magnesium aluminotitanate. Nevertheless, very distinct differences are observed between the samples with different La₂O₃ concentrations. For the sample with x = 0.4, the domains were detected at lower temperatures, while the quantity and size of the domains increase faster due to the promoted precipitation of indialite. For the sample with x = 0.1, in addition to the domain boundaries, secondary boundaries between the “regions” (assemblages of the domains) are observed in a larger length scale. The average size of the crystalline phases found between the “regions” is larger than that typically observed at the domain boundaries. The sizes of the crystals at the boundaries decrease with higher concentrations of La₂O₃, and the crystals (especially perrierite) within the domains become larger, resulting in a more homogeneous microstructure. This results in better dielectric properties, i.e., much higher quality factor for the sample with x = 0.4 in comparison to that with x = 0.1 after heat-treatment at 1150 or 1250 °C.     

Thermodynamic Assessment of EuCl<Subscript>3</Subscript>–MgCl<Subscript>2</Subscript> and EuCl<Subscript>3</Subscript>–BaCl<Subscript>2</Subscript> Systems

Using the CALPHAD technique, an assessment of the binary EuCl₃–MgCl₂ and EuCl₃–BaCl₂ systems has been carried out in this study. The modified quasi-chemical model was defined to describe the Gibbs energies of the liquid phases, and the model parameters were optimized from the experimental phase diagram data. The phase diagrams and enthalpies of mixing of the EuCl₃–MgCl₂ and EuCl₃–BaCl₂ systems were calculated. The calculated results by the present method agree well with the experimental data. The Gibbs energies of formation of Mg₃Eu₂Cl₁₂, Ba₃Eu₂Cl₁₂, and Ba₂Eu₃Cl₁₃ from the pure components were predicted.