Influence of ZrO2 and P2O5 addition on phase formation, optical transmittance and microhardness in lithium disilicate based glass-ceramics

99(1Li2O:2SiO2)-1K2O glasses have been synthesized by a melt quenching technique with the consecutive addition of ZrO2 and P2O5. The addition of ZrO2 decreases the Q2 units and increases the Q3 units due to the formation of Si-O-Zr bonds. Whereas the P2O5 addition increases the fraction of Q4 units while decreasing the Q2 and Q3 units by forming disordered Li3PO4 and Li4P2O7 regions in the glasses. The changes in the fraction of Q2, Q3 and Q4 units affect the crystallization sequence in glass-ceramics. The ZrO2 addition hampers the Li2Si2O5 phase formation and allows the Li2SiO3 phase formation. Whereas, the P2O5 addition promotes the formation of both the Li2Si2O5 and Li2SiO3 phases. For the glass-ceramic containing 2 mol % P2O5, the highest Hv 6.7±0.09 GPa and an optical transmittance 63 % (at a wavelength of 550 nm for the specimen thickness 2 mm) could be achieved.