Flux crystal growth of Ba2TiOSi2O7

• BTS crystal with size up to 18×13×5 mm3 has been grown from the LiF–H3BO3 flux system.
• SHG of BTS is about 5.5 times that of KDP, which is caused by TiO5 polyhedra.
• The polarizations of TiO5 groups are enhanced along c-axis.
• The MF (M=Li, Na, K) and H3BO3 system was found to be a well kind of flux system.

Crystals of Ba2TiOSi2O7 (BTS) with sizes up to 18×13×5 mm3 have been successfully grown from the LiF–H3BO3 flux system. The selection of the flux and the morphology of the crystals were discussed. Through our experiment, the alkali metal fluoride and boric acid system was found to be a flux system that can reduce the system temperature drastically. The crystals exhibit a maximum second harmonic generation (SHG) response about 5.5 times that of KDP at the particle size range of 88–105 μm. The SHG response is mainly caused by the parallel alignment of the TiO5 polar pyramidal polyhedra, and the calculation of local dipole moments shows that the polarizations of all the TiO5 groups are well enhanced along the c-axis. The UV–vis–NIR Diffuse-Reflectance spectrum shows that the ultraviolet cutoff edge for BTS is 240 nm. The powder X-ray diffraction (XRD) pattern of the grown BTS crystals has been indexed.