Structure and phase diagram of the Na2B4O7-Na3AlF6 system

A complex study was carried out on Na2B4O7-Na3AlF6 binary system by means o f differential thermal analyses (DTA), X-ray diffraction as well as infrare d (IR), and Raman spectroscopy. Although the system exhibits a simple eutec tic at 83 wt % Na2B4O7 and T-e = 642 degrees C, interesting structural chan ges of borate glasses formed have been evidenced by means of IR and Raman s pectroscopy. Over 80-100 wt % Na2B4O7 range AlF63- anions are diluted in th e 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 Pu blishers.