Structure and phase diagram of the Na2B4O7-Na3AlF6 system

A complex study was carried out on Na2B4O7-Na3AlF6 binary system by means of differential thermal analyses (DTA), X-ray diffraction as well as infrared (IR), and Raman spectroscopy. Although the system exhibits a simple eutectic at 83 wt % Na2B4O7 and T-e = 642 degrees C, interesting structural changes of borate glasses formed have been evidenced by means of IR and Raman spectroscopy. Over 80-100 wt % Na2B4O7 range AlF63- anions are diluted in the vitreous matrix without significant structural changes while the further increase of Na3AlF6 content diminishes the concentration of BO4 groups and promotes the appearance of complex anions AlFx(x-3)- (x = 6, 5, 4) as well as the possible new BF4- and/or BO3F4- species. (C) 1999 Kluwer Academic Publishers.