Top-seeded growth of Bi₂B₈O₁₅ from a stoichiometric melt is reported. Crystals have been grown with dimensions of up to 24 x 12 x 5 mm³. Bi₂B₈O₁₅ shows twin domains at room temperature; their origin was investigated by methods of thermal analysis. The domains were found to result from a sluggish phase transition that occurs in a broad temperature range (ΔT ~ 20 K) around ~390 K. Unit cell parameters at room temperature were determined: a = 4.3140(6) Å, b = 22.148(2) Å, c = 6.4695(6) Å, β = 105.46(1)°, possible space group P2₁ (no.4), the non-centrosymmetry was proved using powder SHG.

Keywords: bismuth borate, Bi2B8O15, crystal growth, phase transition

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