Processing of β-BaB2O4 powders and thin films through metal alkoxide

Abstract β-BaB 2 O 4 powders and films can be synthesized by the sol-gel method using metal alkoxides. A homogeneous and stable solution was prepared by the reaction of barium metal with boron triethoxide in a mixture of ethanol and 2-ethoxyethanol. The BaB 2 O 4 precursor was confirmed to contain four-coordinated boron by boron-11 nuclear magnetic resonance spectroscopy. Powder as-precipitated from the precursor solution by hydrolysis crystallized to the γ-phase, which was transformed to the β-phase at 600°C. The precursor films prepared by a dip coating crystallized to β-BaB 2 O 4 on Pt(111)/glass substrates at 500°C. The calcination of precursor films in a H 2 OO 2 gas mixture was found to be effective not only for crystallizing into β-BaB 2 O 4 , but also for the preferred orientation of β-BaB 2 O 4 films. β-BaB 2 O 4 films with highly preferred orientation were synthesized on LiTaO 3 substrates at 550°C. The orientation of β-BaB 2 O 4 films was found to depend upon the ligand of the precursor, and to change from (006) to (104) plane with increasing ratio of ethanol/2-ethoxyethanol in the solvent. The β-BaB 2 O 4 film on a Pt sheet showed the second harmonic generation of intense 532 nm light on irradiation with a 1064 nm Nd: YAG laser.