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In this work, we studied the catalytic performance of a β-Bi₂O₃/Bi₁₂SiO₂₀ nanocomposite material in the reactions involving the photodecomposition of rhodamine B and selective photooxidation of 5-hydroxymethylfurfural (HMF). The semiconductor composite nanomaterial was obtained by means of the mechanical grinding of a mixture of nanopowders of β-Bi₂O₃ and sillenite, both individually produced via pulsed laser ablation. The crystal structure of the prepared composite particles was confirmed by means of X-ray diffraction, while the optical properties of both individual components and their composite (with different ratios of Bi₂O₃ and Bi₁₂SiO₂₀) were also studied. The photocatalytic activity of the composite particles was studied in the course of their decomposition of rhodamine B under LED excitation at wavelengths of 375, 410 and 470 nm. It was shown that the optimal β-Bi₂O₃/Bi₁₂SiO₂₀ ratio in the composite particles resulted in their photocatalytic activity exceeding those of both single-phase β-Bi₂O₃ and Bi₁₂SiO₂₀, as well as that of their mixtures (by ~2.3 times for the excitation of an LED with λ = 375 nm). The novel composite particles were also found to perform better in the selective photocatalytic oxidation of HMF: at a conversion of ~5%, the selectivity toward DFF of the nanocomposite was significantly higher (10.3%) than that of sample Bi₂O₃ (−4.2%). A model was proposed that explains the increase in activity of the newly prepared photocatalyst due to the formation of a type II heterojunction in its particles. Full article

The full matrix of electro-elastic constants of sillenite-type crystals Bi₁₂TiO₂₀ (BTO) and Bi₁₂SiO₂₀ (BSO) were determined by the resonance method, with d₁₄ and k₁₄ being on the order of 40–48 pC/N and 31%–36%, respectively. In addition, double-rotated orientation dependence of d₃₃ was investigated, with the maximum values of 25–28 pC/N being achieved in ZXtl45°/54°-cut samples. The electrical resistivity of BSO was found to be two orders higher than that of BTO, being on the order of 7 × 10⁵ Ω cm at 500 °C. The temperature dependence of dielectric and piezoelectric properties were investigated. BSO exhibited a high thermal stability in the temperature range of 25–500 °C, while BTO showed a variation of ~3% in the range of 25–350 °C. The high values of d₁₄ and k₁₄, together with the good thermal stability, make BTO and BSO crystals potential candidates for electromechanical applications in medium temperature range. Full article