| Autor: |
Volkov S; Grebenshchikov Institute of Silicate Chemistry, Makarov Emb, St Petersburg 199053, Russian Federation., Charkin D; Department of Chemistry, Lomonosov Moscow State University, Moscow 119991, Russian Federation., Bubnova R; Grebenshchikov Institute of Silicate Chemistry, Makarov Emb, St Petersburg 199053, Russian Federation., Povolotskiy A; Institute of Chemistry, Saint Petersburg State University, Ulianovskaya st., St Petersburg 198504, Russian Federation., Arsent'ev M; Grebenshchikov Institute of Silicate Chemistry, Makarov Emb, St Petersburg 199053, Russian Federation., Krzhizhanovskay M; Department of Crystallography, Saint Petersburg State University, University Emb. 7/9, Saint Petersburg 199034, Russian Federation., Stefanovich S; Department of Chemistry, Lomonosov Moscow State University, Moscow 119991, Russian Federation., Ugolkov V; Grebenshchikov Institute of Silicate Chemistry, Makarov Emb, St Petersburg 199053, Russian Federation., Kurilenko L; Grebenshchikov Institute of Silicate Chemistry, Makarov Emb, St Petersburg 199053, Russian Federation. |
| Abstrakt: |
The first silver bismuth borate, AgBi 2 B 5 O 11 (silver dibismuth pentaborate), has been prepared via glass crystallization in the Ag 2 O-Bi 2 O 3 -B 2 O 3 system and characterized by single-crystal X-ray diffraction. Its structure is derived from that of centrosymmetric Bi 3 B 5 O 12 by ordered substitution of one Bi 3+ ion for Ag + , which results in the disappearance of the mirror plane and inversion centre. Second harmonic generation (SHG) measurements confirm the acentric crystal structure. It is formed by [Bi 2 B 5 O 11 ] ∞ layers stretched along c and comprised of vertex-sharing B 5 O 10 and BiO 3 groups which incorporate the Ag + cations. The new compound was characterized by thermal analysis, high-temperature powder X-ray diffraction, and vibrational and UV-Vis-NIR (near infrared) spectroscopy. Its thermal expansion is strongly anisotropic due to the presence of rigid B 5 O 10 groups aligned in a parallel manner. The minimal value is observed along their axis [parallel to c, α c = 3.1 (1) × 10 -6 K -1 ], while maximal values are observed in the ab plane [α a = 20.4 (2) and α b = 7.8 (2) × 10 -6 K -1 ]. Upon heating, AgBi 2 B 5 O 11 starts to decay above 684 K due to partial reduction of silver; incongruent melting is observed at 861 K. According to density functional theory (DFT) band-structure calculations, the new compound is a semiconductor with an indirect energy gap of 3.57 eV, which agrees with the experimental data (absorption onset at 380 nm). |
