Disproportionation of Qm (0 ≤ m ≤ 4) species in partially devitrified Li2Si2O5 glasses with small amounts of P2O5

The effect of addition of small amounts of P2O5 in the lithium disilicate glasses results in the scavenging of lithium metal ions by a phosphate group, Li3PO4. As a consequence of the scavenging, the silicate network partially repolymerises. The phosphate group remains intact during heat treatment of the optically clear, X-ray amorphous and slightly nucleated base glasses. However, the relative amounts of the silicate species, Q(m) (0 <= m <= 4), are dependent on the state of the glasses. These amounts, in the optically clear and X-ray amorphous, do not change with heat treatment but they do change, i.e. disproportionation occurs in the slightly nucleated and milky coloured glasses. The disproportionation follows the relation 2Q(3) -> Q(2) + Q(4) which is evident from the relative intensity of the different peaks.