Vol 44, No 4 (2018)

The geometric and topological analysis of the crystal structure of intermetallic Li₂₆Na₅₈Ba₃₈ (cF488, a = 27.335 Å, V = 20 424 ų, F-43m) is carried out using computer methods (ToposPro software package). The analysis method is based on determining the chemical composition and structure of an intermetallic cluster precursor and constructing a basic 3D network of the structure in the form of a graph whose nodes correspond to the position of their centers of gravity. Using the method of the complete decomposition of the 3D factor graph of the crystal structure into cluster substructures, we find two types of framework-forming nanoclusters, namely, K69 of the 1@16@52 composition and K26 of the 0@4@22 composition with point symmetry g =–43m. The symmetric and topological code of self-assembly of 3D structures from nanocluster precursors is reconstructed in the following form: primary chain → microlayer → microframework. Clusters Ba5, Na₆(Na₄), and Na₂В are determined as spacers occupying voids in the 3D framework of nanoclusters K69 and K26.

Six compositions of 1 mol % Dy³⁺-doped multicomponent borate glasses containing single Li₂O, Na₂O, K₂O and mixed Li₂O–Na₂O, Li₂O–K₂O, and Na₂O–K₂O oxides have been synthesized by well-known melt-quenching technique. Following the measured density and refractive index values, various physical parameters were estimated for all the glass samples and differences in them are correlated with structural changes. To explore optical properties like absorption edge (λ_cut-off), optical band gap energy (E_opt), and Urbach energy (ΔE), optical absorption spectra were recorded for all the glasses. The E_g has been calculated using Davis and Mott theory for direct allowed, and indirect allowed transitions and the results were reported. The E_g values are also estimated using absorption spectrum fitting (ASF) method. The optical parameters variations have also been associated with the structural changes occurring in the glasses with different alkali/mixed alkali oxides content presence. The shielding properties of the prepared glasses were studied in terms of effective atomic numbers (Z_eff), mean free path (MFP), half value layer (HVL) and macroscopic effective removal cross-section (Σ_R). From these results, it was found that Potassium (K) glass shows superior gamma ray shielding properties due to a higher value of Z_eff and lower values of both MFP and HVL. These results indicate that the prepared glasses might be utilized in place of some common shielding materials to shield γ-rays and neutrons.

Tb³⁺-doped SrO–Al₂O₃–SiO₂ glass-ceramics are prepared by melting under ambient atmosphere and followed by two-step heat treatment approach. Extensive differential thermal analysis, X-ray diffraction and scanning electron microscope characterizations are applied to investigate thermal properties, crystal structure, and morphology of these glass-ceramics. The results indicate that the optimal ratio of two nucleation agents (TiO₂ and ZrO₂) is 3:1 (molar fraction) in glass-ceramics. In addition, several heat treatment schedules are developed to study the influence of treatment temperature on luminescence properties of Tb³⁺- doped glass-ceramics. The results demonstrate that there are four emission bands located at 489, 547, 588 and 623 nm under 376 nm ultraviolet excitation, corresponding to ⁵D₄ → ⁷F_j (j = 6, 5, 4, 3) transitions of Tb³⁺, respectively. At last, the corresponding chromaticity coordinates are calculated and constructed, which indicates that the Tb³⁺ glass-ceramic can emit approximate white light under 376 nm ultraviolet excitation when they nucleated at 950°C and crystallized at 1050°C. The white immersion approached standard illuminant C as the crystallization temperature increased.

Nanopowders with a composition of (СeO₂)_1–x(Gd₂O₃)_x (x = 0.03, 0.05, 0.07, and 0.10) are synthesized by the coprecipitation method using cryotechnologies. The coherent scattering region (CSR) of the powders is 10–14 nm and the specific surface area is 70–81 m²/g. Based on the powders, ceramic nanosized materials with CRS of 64–71 nm are obtained. The dependence of the phase composition, microstructure, and electrical transport properties of the obtained samples on the Gd₂O₃ content is established. In a CeO₂–Gd₂O₃ system, a solid solution with the composition of (CeO₂)_0.90(Gd₂O₃)_0.10 has the highest ionic conductivity with the transfer number of ions of t_i = 0.74 at a temperature of 700°C. It is shown that ceramics of this composition can be used as a solid electrolyte of intermediate-temperature fuel cells due to their physicochemical characteristics.

This work presents the results of investigating the catalytic activity of potassium titanate nanomaterials doped by different metals (Ni, Mg, Al, Fe, and Cr) in oxidation reactions of hydrogen and carbon monoxide. It is shown that the best characteristics of the oxidation of the investigated gases have nanotubes doped by aluminium (0.3 × 10^–5 mol H₂/(g s) at 250°C and 10^–5mol CO/(g s) at 350°C).

The geometric parameters of the molecular structures of aluminum–iron tetranuclear metal clusters of a stoichiometric composition, AlFe₃ and Al₃Fe, are calculated using the hybrid method of density functional theory (DFT) in the OPBE/TZVP approximation and Gaussian09 software. It is found that the AlFe₃ and Al₃Fe metal clusters can exist in ten and seven structural modifications, respectively; these modifications differ from each other in terms of their stability and geometric parameters. The bond lengths, as well as their bond and dihedral (torsion) angles, are listed for each modification.

Container and sheet glass are synthesized from various batches with the equivalent addition of complexing decolorizers. The effect of ceria and potassium nitrate on the light transmission coefficient is investigated. Measurement of optical characteristics of the glasses shows that light transmittance increases up to 90–93% (λ = 500–750 nm). It is determined that an increase in the concentration of ceria and potassium nitrate up to particular values in the case of each composition results in the increase in hydrolytic stability, TLCE, and the light transmission coefficient.

The relationship between the oxidation-reduction state of rare-earth (RE) elements (Sm, Gd, Eu, Ce, Nd), optical properties and the structural evolution of aluminoborosilicate glasses is studied. The study of the optical characteristics of glass is carried out by measuring optical transmission and analyzing Raman spectra. It is found that the increase in the concentration of monovalent Nd ions leads to the broadening of the optical band of forbidden energies (the band gap Eg), while the larger content of multivalent Sm, Eu, and Ce ions significantly decreases its width. The narrowing of Eg results from the irradiation of glass with a high-energy electron flux (2.5 MeV, a dose of up to 109 Gy). The observed evolution is explained by the coexistence of different charge states and the local environments of RE ions in the studied glass. The presence of different charge states of RE ions causes an increase in the number of color centers, while variations in the local environment of ions change the amount of nonbridging oxygen in the structure.

This article [1] has been retracted at the request of the Editor in Chief because it has been previously published in Journal of Wuhan University of Technology.

Materials Science Edition [2]. This article is therefore redundant. All authors agree to this retraction.

1. Li, H., Liu, L., Tang, X. et al. Glass Phys. Chem. (2017) 43: 548. https://doi.org/10.1134/S1087659617060049

2. Li, H., Liu, L., Tang, X. et al. J. Wuhan Univ. Technol.-Mat. Sci. Edit. (2017) 32: 1025. https://doi.org/10.1007/s11595-017-1706-7