Glasses in the system [50Li 2 O-xB 2 O 3 -(50-x)P 2 O 5 ] (10 < x < 27.5), have been prepared by the melt
quenching technique. Density, molar volume, hardness and Ft-IR spectroscopy have been employed to study the
role of B 2 O 3 on the structure of the glass network. The results of density and hardness showed that both
increased as P 2 O 5 is replaced by B 2 O 5 [as y was increased from 0.2 up to 0.4 where (y = B 2 O 3 /(B 2 O 3 +P 2 O 5 ))].
After Y  0.4 both of them decreased. Infrared spectra reveal that with the replacement P-O-B bonds are present
at very low B 2 O 3 content and their relative amount increased within the whole range of B 2 O 3 . BO 4 tetrahedral
groups are predominant (~ 100%) up to 15 mole% B 2 O 3 . Then, the proportion of BO 3 units starts to appear.