M. Burianek, P. Held, M. Mühlberg: Improved Single Crystal Growth of the Boron Sillenite “Bi24B2O39” and Investigation of the Crystal Structure

Crystal Research and Technology

Cryst. Res. Technol. 37 (2002) 785 - Abstract -

M. Burianek, P. Held, M. Mühlberg

University of Cologne, Institute of Crystallography, Zülpicher Str. 49 b, 50674 Cologne, Germany

Improved Single Crystal Growth of the Boron Sillenite “Bi₂₄B₂O₃₉” and Investigation of the Crystal Structure

The boron sillenite, up to now known as the 12:1 compound Bi24B2O39 in the system Bi₂O₃ – B₂O₃ and crystallizing in the space group I23, melts incongruently at 655 °C only about 25 K above the eutectic tie line and corresponding to a steep liquidus line. Single crystals with dimensions larger then 1 cm³ have been successfully grown in [100], [110], and [111] direction by an improved Top Seeded Solution Growth (TSSG) technique equipped with crucible weighing, accelerated crystal rotation technique and air-cooled pulling rod. The structure of the boron sillenite was analyzed by X-ray diffraction method, which was possible due to the high crystalline quality achieved. A defect-free sublattice corresponding to a Bi-O framework is isostructural with all sillenites, but a 2 Å environment around the origin is occupied by different cations with different population coefficients. The best calculation results in the formula Bi_24.5BO_38.25 which is more Bi-rich than the 12:1 assumption.

Keywords: boron-sillenite, incongruent melting, crystal growth by the TSSG method, structure analysis, corrected chemical formula Bi24B2O39 to Bi24.5BO38.25

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