Vol 59, No 2 (2023)

We have studied properties of p-type Bi0.5Sb1.5Te3 solid solution samples produced by hot pressing, extrusion, and spark plasma sintering of powders prepared by melt spinning and grinding the ingot in a jet mill to a particle size on the order of hundreds of microns or less than hundreds of nanometers (by mechanical activation). The powders and fracture surfaces of the samples have been examined on an optical and a scanning electron microscope. The powders prepared by melt spinning at disk rotation rates of 3000 and 5500 rpm had the form of platelets tens of microns in thickness, consisting of distinct regions ranging in thickness from a few to hundreds of nanometers. Microstructural analysis showed that all of the samples contained a small amount of tellurium, which was confirmed by X-ray microanalysis data. We have measured the thermoelectric parameters (Seebeck coefficient, electrical conductivity, and thermal conductivity) of the materials at room temperature and in the range 100–700 K and calculated their lattice thermal conductivity and thermoelectric figure of merit, ZT. The highest thermoelectric figure of merit, ZT = 1.0 ± 0.1 at 380 K, has been reached in the samples produced by spark plasma sintering and hot pressing of powders prepared by melt spinning and mechanical activation, respectively.

Low-temperature phase formation processes (below 1270–1450°C) underlying aluminothermic reduction of titanium from different TiO2 polymorphs—stable rutile and metastable anatase—have been studied during continuous heating and isothermal heat treatment. Interaction between the components has been investigated at TiO2/Al molar ratios of 0.23 and 0.43 using thermal analysis and X-ray diffraction. The results demonstrate that, in the case of continuous heating of anatase + aluminum powders with TiO2/Al = 0.43, the reduction process begins at a temperature of 943°C and does not reach completion up to 1270°C, resulting in the formation of the intermetallic phase Al3Ti, Al2O3, and intermediate titanium oxides (Ti0.78O0.937 and (Ti0.99Al0.01)2O3). Increasing the fraction of aluminum in the mixture (TiO2/Al = 0.23) increases the degree of reduction of titanium, which shows up as an increase in the amount of intermetallic phases (Al3Ti, Al2Ti, Al1.1Ti0.9, and AlTi3) in the reduction products and a decrease in the amount of intermediate titanium oxides. Rutile has been shown to have low reactivity: heating of rutile + aluminum mixtures to 1450°C leads to the formation of many intermediate titanium oxides along with a small amount of Al3Ti and AlTi3. The results have been confirmed by isothermal heat treatment (1400°C, 60 min) of mixtures of anatase and rutile with aluminum. The anatase-to-rutile polymorphic transformation during heating in flowing argon has been shown to occur in the range 622–913°C. During the reduction process, molten aluminum inhibits the phase transition of anatase, but its reactivity remains higher than that of rutile

Zr–B–Si–C–Ti and Zr–B–Si–C–Ti–N coatings have been produced for the first time by an arc physical vapor deposition process in a residual argon + nitrogen atmosphere. The Zr–B–Si–C–Ti coating had an amorphous–nanocrystalline structure. Nanocrystallites were formed in the Ti–B–C system, and the amorphous component of the material was formed by Zr–B–C and Si–C phases. The coating of the latter system had a predominantly amorphous structure (amorphous content of ~85–93%) based on titanium nitride with Ti–B and Ti–C bonds, zirconium carboboronitride (Zrx(C,N,B)y), zirconium boride, and silicon carbonitride.

This paper reports on the synthesis of terbium sesquioxide (Tb2O3) nanoparticles via laser ablation of a solid target in a flowing 95% Ar + 5% H2 binary welding mixture with the use of an ytterbium-doped fiber laser with an average output power of 300 W. We have studied morphological and structural features of the synthesized powder, its thermal behavior, magnetic properties, and densification dynamics during heating to 1450°C in vacuum. The synthesized particles were nearly spherical in shape, with an average size of 13 nm, and had a monoclinic crystal structure, which irreversibly transformed into a cubic structure of 
 symmetry as a result of firing in argon or vacuum at temperatures near 750 and 1050°C, respectively. Using temperature-dependent specific magnetization measurements, we determined their paramagnetic Curie temperature (θp = –11.8 K), Curie constant (C = 11.74 K emu/(mol Oe)), and effective magnetic moment (μeff = 9.69μB/Tb). These data suggest that antiferromagnetic exchange interaction between the terbium ions prevails and that the content of Tb4+ ions in the nanopowder is negligible. We have demonstrated the feasibility of producing transparent Tb2O3 ceramics by consolidating presintered nanoparticles via hot isostatic pressing for 2 h at a temperature of 1450°C and pressure of 200 MPa.

Using normal pull-off testing, we have studied adhesion contact strength in the GaxGe40–xS60–quartz glass system as a function of contact formation temperature, pull-off test temperature, and chalcogenide glass composition. The addition of 1 at % gallium to glass composition considerably reduces the adhesion strength. Further increasing the percentage of gallium, to 8 at %, causes only a slight drop in adhesion. The observed general relationships can be accounted for by partial glass crystallization on heating for adhesion contact formation and subsequent cooling to the pull-off test temperature. We have formulated recommendations concerning detachment of GaxGe40–xS60 glasses from the quartz reactor wall.

Compact stoichiometric zirconium carbide (ZrC) with a tailored shape has been synthesized by direct carburization of rolled zirconium metal in an atmosphere of an argon + ethylene gas mixture. Ceramics have been produced by reacting zirconium metal with ethylene gas, through absorption of the carbon released on the reaction surface as a result of C2H6 pyrolysis. We have characterized the microstructure of the ceramics and assessed the mechanical and conductive properties of the synthesized ZrC.

An approach has been proposed for preparing polymerizable precursors to alpha-alumina and aluminum oxynitride ceramics and using them in stereolithographic fabrication of aluminum-containing ceramics. With allowance for their homogeneity (optical transmission), photopolymerizability, and weight loss during thermolysis, three precursors based on aluminum chlorides (anhydrous and hexahydrate) and a basic aluminum chloride were chosen for characterization. We analyzed the behavior of the precursors during firing in an ammonia atmosphere for the preparation of oxynitride ceramics and during firing in air for the preparation of alpha-alumina ceramics from homogeneous precursors. Stereolithographic 3D printing of alpha-alumina ceramics was tested, in particular with the use of the proposed precursors in the form of photopolymerizable binders allowing the fraction of alumina in photosuspensions to be increased.

Electrical transport properties of a composite material based on ultrahigh molecular weight polyethylene having NiO nanoparticles deposited on its granules have been investigated using impedance spectroscopy. This has made it possible to study electrical engineering properties of an ensemble of nanoparticles uniformly distributed over a polymer matrix. We have evaluated the dielectric permittivity, capacitance, and dielectric loss tangent of the composite and found frequency dependences of the real and imaginary parts of its complex conductivity. The hopping conduction mechanism has been shown to prevail in the composite at frequencies of up to 1 MHz, giving way to a relaxation mechanism at higher frequencies. We discuss a correlation between structural features of the composite and charge transport processes.