b-BaB2O4 (BBO) crystals were grown from high-temperature borate solutions by the top seeded growth method (TSGM) using NaF as a flux. During the crystal growth, volatiles were found to cause defects in BBO crystals. The component of volatiles was investigated to be sodium fluoride (NaF) by X-ray diffraction. Optical microscope and electron microscope were used to identify inclusions in BBO crystals. Two mechanisms for the formation of inclusions caused by the volatilization of NaF were discussed and the inclusion free BBO crystals with 70 mm in diameter and 20 mm in thickness were obtained. (C) 2004 Elsevier B.V. All rights reserved.