Influence of Grain Structure Features on the Thermoelectric Properties of Compounds Based on Bismuth Telluride

Glass and Ceramics - An analysis of the specific mechanisms of the influence of the state of the grain structure on the thermoelectric properties (electrical resistivity and total thermal...     

Synthesis and electrical properties of Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript>-based thermoelectric materials doped with Er,Tm, Yb,and Lu

Nanopowders of Bi₂Te₃ and R_0.1Bi_1.9Te₃ (where R = Er, Tm, Yb, Lu) are obtained by microwave solvothermal synthesis. The powder-like materials are compacted by cold isostatic compression followed by annealing in argon. The influence of the doping agent on the structure and characteristics of the derived materials are investigated. It is demonstrated that the introduction of rare-earth elements (2 at %) into the bismuth-telluride lattice leads to a decrease in the electrical resistivity and to an increase in the Seebeck coefficient. The best thermoelectric properties are obtained for the sample of bismuth telluride doped with thulium.     

Ultrasonic disintegration of tungsten trioxide pseudomorphs after ammonium paratungstate as a route for stable aqueous sols of nanocrystalline WO<Subscript>3</Subscript>

A new facile method is proposed for the preparation of aqueous sols of highly crystalline tungsten trioxide with a particle size of 60–150 nm, containing no organic stabilizers/surfactants. These sols possess high sedimentation stability, which is quite unusual for inorganic colloidal systems containing relatively large particles, with a rather high density (ρ _c(WO₃) = 7.3 g/cm³). The method is based on the thermal decomposition of ammonium paratungstate, followed by dispersing the resulting powders in water under ultrasonic treatment. Thermal decomposition of ammonium paratungstate, and the composition and structure of the resulting tungsten trioxide and its aqueous dispersions, were investigated with thermal analysis combined with the mass spectrometry of gaseous thermolysis products, powder X-ray diffraction, scanning electron microscopy, low-temperature nitrogen adsorption, IR spectroscopy and dynamic light scattering. It has been demonstrated that the high sedimentation stability of WO₃ results from electrostatic stabilization, which might be caused by the formation of tungstic acid on the surface of WO₃ particles when they come into contact with water. The nanocrystalline WO₃ obtained can be used to produce gas sensors for ammonia.     

Preparation of crystalline Mg(OH)_2 nanopowder from serpentinite mineral

In this paper we describe a route to produce crystalline Mg(OH)2 nanopowders from serpentinite ore distributed in the Halilovskiy array(Russia, Orenburg region). An efficient extraction route consisting of treatment on serpentinite in 40% HNO_3 at 80 °C followed by NH_4OH titration for Mg(OH)_2 precipitation was demonstrated. In this study, crystalline Mg(OH)2 nanopowders have been synthesized by solvothermal reaction method using(Mg(NO_3)_2á6H_2O) which were obtained from serpentinite, NH4 OH as a precipitator, and hydroxyethylated nonylphenol as surface-active substance. Microstructure and phase composition of samples were investigated employing scanning electron microscopy(SEM) and transmission electron microscopy(TEM), X-ray phase analysis(XRD), and inductively coupled plasma optical emission spectroscopy(ICP-OES). XRD reveals that Mg(OH)2 nanopowder with high purity has the brucite structure. It was found that crystalline Mg(OH)_2 nanopowders exclusively consist of lamellar-like structures and the sizes of Mg(OH)_2 are 30–265 nm length or width.     

Intercalation of Porphyrin‐Based SURMOF in Layered Eu(III) Hydroxide: An Approach Toward Symbimetic Hybrid Materials

A strategy for rational design of synergetic hybrid materials exploiting stabilization of intercalated layered matrices via coordination bonding is described. A new hybrid material is assembled through subsequent intercalation of the surface‐anchored metal–organic framework (SURMOF) components, zinc acetate and 5,10,15,20‐tetrakis(4‐carboxyphenyl)‐porphyrin‐zinc(II) (ZnTCPP), into the layered europium(III) hydroxychloride (LEuH). The formation of the SURMOF clusters intercalated in LEuH is confirmed by X‐ray diffraction, FTIR and Raman spectroscopy, and BET nitrogen absorption methods. The catalytic function of the SURMOF/LEuH hybrid and its components in the model reaction of hydrolysis of bis(4‐nitrophenyl) phosphate in the acidic solution is studied by UV–vis and MALDI‐TOF spectroscopy. Both the non‐intercalated matrix and the MOF powder are inactive and unstable in the substrate solution. Unlike its components, the SURMOF/LEuH hybrid exhibits synergetic catalytic activity increasing with the amount of the intercalated compounds because of the mutual stabilization of the components through coordination interactions. The results provide a basis for symbimetic (mimicking the symbiotic behavior in biological systems) hybrid materials, in which stabilization of functional units in the intercalated structure translates into a synergy of useful properties.     

Effect of Spark Plasma Sintering Temperature on Thermoelectric Properties of Grained Bi1.9Gd0.1Te3 Compound

Semiconductors - Patterns in changes of the microstructure (grain structure) and the thermoelectric properties of the n-type grained Bi1.9Gd0.1Te3 compound, spark-plasma-sintered at different...     

Synthesis of nanocrystalline ZrO<Subscript>2</Subscript> with tailored phase composition and microstructure under high-power sonication

The effect of sonication on the composition and properties of zirconia precipitated from aqueous zirconyl nitrate solutions at various pH values has been studied using thermal analysis, X-ray diffraction, and low-temperature nitrogen adsorption measurements. The results demonstrate that acoustic processing considerably reduces the content of sorbed ions in amorphous ZrO₂ · xH₂O gels and allows one to control the composition and microstructure of the nanocrystalline zirconia produced through thermal decomposition of the gels.     

Thermoelectric Properties of Bi2 –xLuxTe2.7Se0.3 Solid Solutions

Semiconductors - The thermoelectric properties of compounds based on Bi2 –xLuxTe2.7Se0.3 solid solutions with x = 0, 0.05, 0.1, and 0.2 are studied. The samples for investigations are...     

Influence of the Sintering Temperature on the Thermoelectric Properties of the Bi1.9Gd0.1Te3 Compound

Semiconductors - The regularities of the influence of the sintering temperature (750, 780, 810, and 840 K) on the elemental composition, crystal-lattice parameters, electrical resistivity, Seebeck...