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We studied the influence of doping with 4d and 5d elements on the optical and photo-induced properties of Bi12SiO20 (BSO) crystals. Doping with Ru, Rh and Re does not significantly influence BSO absorption spectra as well as photo-induced absorption and photocurrent in BSO. On the other hand, doping with Os with concentration of 0.0004 mass% increases by more than an order of magnitude the illumination response time, the strength of the photochromic effect and photocurrent, all this being accompanied by only a slight change of the absorption coefficient as compared to undoped BSO. The observed effects are explained in the framework of the Rose model assuming that doping with Os creates deep levels in the gap that act as recombination centers with a very little cross-section of electron capture. We also studied the kinetic curves of photocurrent increase and decrease in BSO:Os which enabled us to determine the magnitude of the cross-section of a photon capture at an impurity center. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Single crystals of the new title compound are prepared by cooling a melt of composition 14.3 mol% BaO, 7.1 mol% Bi2O3, and 78.6 mol% B2O3 (Pt crucible, 850 °C, 20—24 h).

Single crystals of α- and β-polymorphs of Bi2B8O15 were grown by Czochralski method from a charge of the stoichiometric composition. The crystal structure of β-Bi2B8O15 was solved by direct methods from a twinned crystal and refined to R1=0.081 (wR=0.198) on the basis of 1584 unique observed reflections (I>2σ(I)). The compound is triclinic, space group P 1 ¯ , a=4.3159(8), b=6. 4604(12), c=22.485(4) A, α=87.094(15)°, β=86.538(15)°, γ=74.420(14)°, V=602.40(19) A3, Z=2. The B–O layered anion of β-Bi2B8O15 is topologically identical to the anion of α-Bi2B8O15 but the orientation of neighboring layers is different. Thermal expansion of α-Bi2B8O15 has been investigated by X-ray powder diffraction in air in temperature range from 20 to 700 °C. It is strongly anisotropic, which can be explained by the hinge mechanism applied to chains of Bi–O polyhedra. While the anisotropy of thermal expansion is rather high, the volume thermal expansion coefficient αV=40×106 °C−1 for α-Bi2B8O15 is close to those of other bismuth borates.

A new compound, SrBi 2 B 4 O 10 , has been grown by cooling a melt with the stoichiometric composition. It is triclinic, P −1, a =6.819(1), b =6.856(1), c =9.812(2) A, α= 96.09(1), β =109.11(1), γ =101.94(1)°, V =416.5(1) A 3 , Z =2. The crystal structure of the compound has been solved by direct methods and refined to R 1 =0.050 (w R 2 =0.128). The structure contains Bi–O pseudolayers build up from Bi–O chains involving oxocentred OBi 3 triangles. Sr atoms and [B 4 O 9 ] 6− isolated anions (4B:3 Δ □: Δ □> Δ ) are located between the Bi–O packages. The thermal treatment as well as DSC experiment showed that the compound melts above 800 °C presumably according to the peritectic reaction: SrBi 2 B 4 O 10 ↔ SrB 2 O 4 +SrB 4 O 7 + Liquid. According to high-temperature X-ray powder diffraction study thermal expansion of SrBi 2 B 4 O 10 structure is anisotropic ( α 11 =13, α 22 =9, α 33 =2, α V =24×10 −6 °C −1 ).