Kyropoulos Growth and Characterization of Monoclinic α-Bi2B8O15 Single Crystal with Noncentrosymmetric Structure
Monoclinic bismuth-based borate crystal α-Bi2B8O15 was grown by the Kyropoulos method. High resolution X-ray diffraction analysis showed that the full width at half-maximum of the Y plate was about 0.04° for α-Bi2B8O15 crystal. The ideal morphology of the α-Bi2B8O15 crystal was analyzed based on the refined structure obtained by the Rietveld method and it was found that the α-Bi2B8O15 crystal had a layered structure along the b axis. The X-ray photoelectron spectroscopy, density, mechanical and thermal properties, transmission spectrum, and electrical resistivity of the α-Bi2B8O15 crystal were studied. Furthermore, the opto-electric properties were evaluated from the perspective of structural distortion. Results support that the α-Bi2B8O15 crystal possesses good chemical and thermal stability. The specific heat (0.61 J·g-1·K-1) was larger than that of the α-BiB3O6 crystal (0.48 J·g-1·K-1) at room temperature. In addition, the α-Bi2B8O15 crystal had a relatively large band gap (4.41 eV) and a wide transmission range (260 nm~4.43 μm). The infrared cut-off edge was 4.43 μm, larger than other borate crystals, such as β-BaB2O4, CsB3O5, and LiB3O5 crystals. Besides, a high electrical resistivity was observed for the α-Bi2B8O15 crystal and reached as high as 1.5×1010 Ω·cm at 300 °C along the Y axis, nearly two orders of magnitude higher than that of the La3Ga5SiO14 crystal (~8×108 Ω·cm). The multifunctional α-Bi2B8O15 crystal may have potential for opto-electric applications.