A STRUCTURAL APPROACH TO (1-X)NAPO3-CENTER-DOT-XNA2B4O7 GLASSES - THECORRELATION OF STRUCTURE WITH PHYSICAL AND CHEMICAL-PROPERTIES

Vibrational (infrared and Raman) and NMR (P-31 MAS, B-11) results of g lasses belonging to the pseudo binary (1-x)NaPO3.xNa2B4O7 system are s ummarised. Structural models are proposed as a function of x. In the p hosphate rich compositional region (0 < x less-than-or-equal-to 0.2) t he addition of the Na2B4O7 produces a shortening of the metaphosphate chain lengths. For the higher phosphate concentration (x less-than-or- equal-to 0.05) the boron atoms, mainly of the B(cIV) O4/2- unit form, compensated by phosphate units, interconnect the phosphate chains, wit h a random branching tendency and the formation of borophosphate group s of the form (O3/2B(cIV)OP(c)O5/2)2- and (O3/2B(cIV)OP(c)O4/2)-. For x close to 0.2 the glasses are built up with B(IV)O4/2- and/or B(III)O 3/2 units which connect 'isolated' phosphate entities to form not only (O3/2B(cIV)OP(c)O5/2)2- and (O3/2B(cIV)OP(c)O4/2)- but also (O3/2B(IV )OPO5/2)- and (O2/2B(III)OPO5/2)- borophosphate groups. The borate ric h glasses are formed by some O2/2PO2- phosphate units inserted in 'bor ate like' network. For higher borate concentrations some O1/2PO3(2-) e nd groups and perhaps PO4(3-) isolated monomers are present in the gla ss. The physical and chemical properties are correlated with the diffe rent structural models.