PROCESSING OF BETA-BAB2O4 POWDERS AND THIN-FILMS THROUGH METAL ALKOXIDE

beta-BaB2O4 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 BaB2O4 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 gamma-phase, which was transformed to the beta-phase at 600 degrees C. The precursor films prepared by a dip coating crystallized to beta-BaB2O4 on Pt(111)/glass substrates at 500 degrees C. The calcination of precursor films in a H2O-O-2 gas mixture was found to be effective not only for crystallizing into beta-BaB2O4, but also for the preferred orientation of beta-BaB2O4 films. beta-BaB2O4 films with highly preferred orientation were synthesized on LiTaO3 substrates at 550 degrees C. The orientation of beta-BaB2O4 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 beta-BaB2O4 film on a Pt sheet showed the second harmonic generation of intense 532 nm light on irradiation with a 1064 nm Nd:YAG laser.