Vol 53, No 5 (2017)

Using chemical vapor transport, we have grown AgGaS₂ single crystals possessing large room-temperature X-ray induced conductivity and X-ray sensitivity coefficients, which allows the single crystals to be recommended for use as key elements of various uncooled and very fast X-ray detecting devices and systems.

The surface composition and morphology of a carbon matrix/Mo₂C composite have been studied by scanning electron microscopy and X-ray photoelectron spectroscopy. The results demonstrate that the carbon matrix has the form of entangled filaments of carbon nanotubes. The surface layer of the composite contains 57 carbon atoms per molybdenum atom. Molybdenum is present here in the form of the Mo₂C carbide (39 at %) and the Mo₂O₅ (50 at %) and MoO₂ (11 at %) oxides, with E_b(Mo 3d_5/2) = 228.2, 229.6, and 231.9 eV, respectively. The presence of the Mo⁴⁺ and Mo⁵⁺ oxides in the surface layer is due to active reaction of the Mo₂C in the composite with atmospheric oxygen and moisture during the sample preparation process and can be accounted for by the small particle size of the material. Based on analysis of the structure of the C 2s and C 2p valence electron spectra, we assume that the carbon nanotubes of the composite are graphitelike carbon structures. The composite studied here does not become charged when exposed to an X-ray beam, which suggests that it is a weak dielectric.

Thin samples (about 4 μm in thickness) of membrane foil of a Pd–Cu solid solution have been grown on the surface of a SiO₂/Si heterostructure by magnetron sputtering. The key features of \(\beta \rightleftharpoons \alpha \) phase transformations have been identified using X-ray diffraction, Auger electron spectroscopy, energy dispersive X-ray microanalysis, and resistivity measurements during a heating–cooling cycle. The results demonstrate that the phase transformations are reversible only in solid solutions containing an excess of copper in the concentration range corresponding to limiting temperatures near the temperature stability limit of the β-phase. Thermal conditions of membrane element operation have been found that ensure stability of the ordered atomic structure of the foil and, accordingly, its high performance. The \(\beta \rightleftharpoons \alpha \) phase transformation has been shown to be reversible after holding the foil at t = 830°C, in a state with a disordered atomic structure, which ensures restoration of its high hydrogen permeability after diffusion bonding to the case of a membrane element.

Nanocrystalline BaZrO₃ has been prepared by solid-state reaction, using preliminary mechanical activation of a stoichiometric mixture of BaCO₃ and ZrO₂. The mechanical activation was performed in an AGO-2 centrifugal planetary mill for 10 min at a centrifugal factor of 40g. The effect of mechanical activation of the reactant mixture on the processes that take place during subsequent heating of the mixture has been studied using a combination of thermoanalytical techniques. The synthesized barium zirconate, with an average crystallite size from 50 to 100 nm, has been characterized by X-ray diffraction and scanning and transmission electron microscopy.

Yb₂Sn₂O₇ and Lu₂Sn₂O₇ have been prepared by solid-state reactions, by firing mixtures of Yb₂O₃ or Lu₂O₃ and SnO₂ at 1473 K, and the molar heat capacity of these compounds (pyrochlore structure) has been determined by differential scanning calorimetry. The C_p(T) data have been used to evaluate the thermodynamic properties of the stannates: enthalpy increment, entropy change, and reduced Gibbs energy.

The Tl–I system has been studied using differential thermal analysis, X-ray diffraction, and emf measurements on TlI concentration cells. A more accurate Tl–I phase diagram is presented, according to which the compounds existing in the Tl–I system are TlI, Tl₂I₃, and TlI₃. Thallium monoiodide melts congruently at 715 K and undergoes a polymorphic transformation at 440 K. The other iodides melt peritectically at 535 and 404 K, respectively. In contrast to what was reported previously, no compound of composition Tl₃I₄ has been obtained. Using experimental emf data, we evaluated relative partial molar thermodynamic functions of the TlI in alloys of the TlI–I system and the standard Gibbs free energy, enthalpy of formation, and standard entropies of TlI₃ (−ΔG₂₉₈⁰= 142.79 ± 0.73 kJ/mol, −ΔH₂₉₈⁰= 135.37 ± 2.85 kJ/mol, and S₂₉₈⁰= 263.3 ± 7.4 J/(mol K)) and Tl₂I₃ (271.39 ± 1.47, 262.40 ± 5.34, and 322.8 ± 13.2).

Osteoconductive ceramic implants based on Ca_3–xM_2x(PO₄)₂ (M = Na, K) double phosphates and having the Kelvin structure, tailored macropore size (in the range 50–750 μm), and a total porosity of 70–80% have been produced by stereolithographic 3D printing. We demonstrate that, to maintain the initial geometry of a model and reach sufficiently high strength characteristics of macroporous ceramics (compressive strength up to 9 MPa and fracture toughness up to 0.7 MPa m^1/2), the polymer component should be removed under specially tailored heat treatment conditions. Based on our results on polymer matrix destruction kinetics, we have found heat treatment conditions that ensure a polymer removal rate no higher than 0.1 wt%/min and allow one to avoid implant cracking during the firing process.

This paper presents results of a detailed study of fundamental aspects of the formation of 2D and 3D nanostructured YSZ:Yb³⁺ ceramics with a cubic structure through a key synthesis step in aqueous solutions of zirconium-containing hydroxy nanoparticles (1–2 nm) modified by Y³⁺ and Yb³⁺ ions, with the use of a sol–gel method and subsequent calcination of the resultant xerogels at temperatures above 350°C. As starting chemicals for the synthesis of ceramic powders, we used zirconyl, yttrium, and ytterbium nitrates and chlorides and aqueous ammonia. Using mixed solutions of these salts and a procedure developed by us, we synthesized sols, gels, and xerogels. To examine the effect of temperature on solid-state transformations, the xerogels were calcined according to a predetermined program in a muffle furnace at temperatures in the range from 350 to 1350°C (rarely, up to 1650°C). We focused primarily on ceramic powders close in composition to 0.86ZrO₂ · 0.10Y₂O₃ · 0.04Yb₂O₃. The ceramics were characterized by high-resolution transmission electron microscopy, electron microdiffraction, electronic diffuse reflectance spectroscopy, energy dispersive X-ray microanalysis, and X-ray fluorescence analysis.