Fabrication of surface crystallized glasses with α-Zn ₃B₂O₆ and their optical property

Surface crystallization of metastable α-Zn₃B ₂O₆ was observed in ZnO-B₂O₃-CaO- K₂O-Al₂O₃ glass after conventional heat treatment. Precipitation of α-Zn₃B₂O₆ with high orientation degree in the transparent glass-ceramics was confirmed by XRD measurement. Transmission electron microscope image showed that crystalline rods of α-Zn₃B₂O₆ were precipitated from the surface of the glass-ceramics with the crystalline orientation of (1 - 2 1) direction. Although the strongly oriented phase was observed in the glass-ceramics, the polarization direction was not strong from the crystal that can bring strong second harmonic generation (SHG). SHG measurement using a powder sample showed that the 2nd optical nonlinearity of α-Zn ₃B₂O₆ glass-ceramics was comparable to that of α-SiO₂.