We have studied the catalytic activity of Cu–Ni bimetallic catalysts on yttrium-, tin-, zinc-, and niobium-doped zirconia and ceria supports for methanol steam reforming (MSR), a process for hydrogen production, and examined the effect of the nature of the dopants and annealing temperature on the structure and particle size of the oxide supports and the catalytic activity of the metal oxide composites. In all cases, the addition of heterovalent ions improved the catalytic activity of the materials for the MSR process in comparison with undoped zirconia. The highest hydrogen yield was reached in the case of catalysts doped with niobium and yttrium oxides.
We have studied and optimized conditions for spontaneous flux growth of TbCr3(BO3)4 crystals. Phase relations in the pseudoternary system TbCr3(BO3)4–K2Mo3O10–B2O3 have been studied in the temperature range 900–1130°C and the single-phase terbium chromium borate crystallization field has been mapped out. It has been shown that increasing the TbCr3(BO3)4 content of the starting high-temperature solution leads to a rhombohedral-to-monoclinic phase transition. Using K2Mo3O10-based high-temperature solutions, we have grown single-phase TbCr3(BO3)4 single crystals or crystals in which the rhombohedral phase (sp. gr. R32) significantly prevails over the monoclinic phase (sp. gr. C2/c). The grown crystals have been characterized by X-ray diffraction techniques, IR spectroscopy, and magnetic measurements.
We have synthesized hybrid membranes based on N-phosphorylated polybenzimidazole, containing different percentages of silica (2–20 wt %). The materials have been characterized by scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, IR spectroscopy, and impedance spectroscopy. The membranes have been shown to contain silica nanoparticles with a bimodal size distribution: 3–5 and 20–60 nm. The hybrid membranes have high proton conductivity (9.7 mS/cm at 130°C), which has a maximum when the dopant content is 2–10 wt %. The phosphonic groups grafted onto the polymer ensure additional hydration of the membranes at increased humidity. The addition of silica helps to reduce the gas permeability of the membranes by a factor of ~1.5
We have studied the effect of surface modification with acids and subsequent heat treatment on the properties of hydrous zirconia. It has been shown that surface modification with phosphate and sulfate groups makes it possible not only to control the phase composition of the heat-treated oxide but also to considerably suppress particle growth. We have discussed the processes involved and shown that, in the initial stages of thermolysis, the process leads to the formation of metastable, tetragonal ZrO2, which transforms into monoclinic zirconia at higher temperatures. Surface modification with phosphoric acid stabilizes tetragonal zirconia up to 850°C.
Single-phase Sr1– x – yYbxEuyF2+ x + y solid solutions with an average particle size near 90 nm have been synthesized via co-precipitation from aqueous solutions, followed by high-temperature annealing. Efficient Yb3+ luminescence was observed upon excitation at a wavelength of 266 nm. The highest external quantum yield of ytterbium luminescence (2.5%) under pumping at a wavelength of 266 nm was reached for the SrF2:Yb(1.0 mol %),Eu(0.05 mol %) composition.
We report the first systematic study of the effect of oxidizing annealing on the superconducting transition temperature Tc of Bi2Sr2 – xLaxCuO6 + δ crystals. Using a standard heat treatment procedure, we have obtained detailed Tc(x) data for Bi2Sr2 – xLaxCuO6 + δ crystals in the range x = 0.35–0.75. Comparison of the shape of the Tc(x) curve for Bi2Sr2 – xLaxCuO6 + δ with that for La2 – xSrxCuO4 demonstrates a factor of 4 reduction in the dependence of hole concentration in the CuO2 planes from a La3+ substitution on the Sr2+ sites becouse oxygen content (or index) varies. This finding can be accounted for in terms of changes in the amount of oxygen vacancies in the SrO planes. In particular, the oxygen index in Bi2Sr2 – xLaxCuO6 + δ varies by 0.3 per formula unit.
The processes occurring during the solid-state synthesis of germanium-doped lithium titanium phosphate have been studied. The formation of LiTi2 – xGex(PO4)3 has been shown to proceed through the titanium pyrophosphate formation followed by its transformation into materials with the NASICON structure. The process is completed at 1073 K. To produce ceramics with an optimal conductivity, annealing at 1173 K is required. Based on the results obtained, a two-stage synthesis procedure was developed. The highest ionic conductivity (3.9 × 10–5 Ohm–1 cm–1 at 433 K) and the lowest activation energy (46 ± 1 kJ/mol) were observed for LiTi2 – xGex(PO4)3 materials with a titanium substitution degree of 20–25% (x = 0.4–0.5). It can be attributed to an optimal size of lithium transport channels.
Order–disorder phenomena in nanocrystalline Gd2ZrO5 and Gd2HfO5 with highly imperfect fluorite- derived structures in the range 1000–1600°C have been studied using monochromatic synchrotron X-ray diffraction and Raman spectroscopy. The results demonstrate that the synthesis process leads to the formation of two coherent phases identical in composition: a nanocrystalline disordered fluorite-like (F) phase (Fm3m) and a nanoparticulate ordered fluorite derivative (C1) (Ia3). Their lattice parameters have been determined. In the range 1000–1600°C, the Raman spectra of the Gd2ZrO5 and Gd2HfO5 materials contain broad bands in low- and high-frequency regions, at ~118 (108), 362 (353), and 670 (665) cm–1, which characterize the C1 and F phases, respectively.