Effects of dopants with various valences on densification behavior and phase composition of a ZrO2–SiO2 nanocrystalline glass-ceramic

Effects of dopants with different valences on the densification behavior and phase composition of a ZrO 2 –SiO 2 nanocrystalline glass-ceramic (NCGC) during pressureless sintering were investigated in this study. The raw powder of Ca 2+ , La 3+ , Ce 4+ and Ta 5+ ions doped ZrO 2 –SiO 2 (referred to as Ca-ZS, La-ZS, Ce-ZS, Ta-ZS, respectively) and pure ZrO 2 –SiO 2 (PZS) sample were synthesized by sol-gel method, followed by pressureless sintering. Compared with the PZS sample, doping of Ca 2+ and La 3+ ions significantly promoted the densification of the NCGCs. The “densification promotion” effect was attributed to the formation of oxygen vacancies and the decrease of SiO 2 viscosity due to doping of aliovalent cations. The dopants with various valences showed significant effects on the phase compositions of the NCGCs during sintering. Doping of Ca 2+ ion accelerated the reaction kinetics between ZrO 2 nanocrystallites and amorphous SiO 2 to yield ZrSiO 4 . The La 3+ ion acted as destabilizer of t-ZrO 2 , which resulted in a rapid tetragonal (t) to monoclinic (m) ZrO 2 phase transformation during sintering, while in the Ta 5+ and Ce 4+ ions doped sample, the phase transformation occurred gradually. All the doping ions increased the lattice parameters and the volume of t-ZrO 2 unit cell, while the effects of the doping ions on the lattice parameters of m-ZrO 2 unit cell were more complex.