Doping of tantalum, niobium, and hafnium in a translucent ZrO2-SiO2 nanocrystalline glass-ceramic

The addition of dopant(s) is an effective strategy to regulate the microstructure and properties of ZrO 2 -based ceramics. In this study, we investigated the effects of ternary element alloying, namely tantalum (Ta), niobium (Nb), and hafnium (Hf) elements, on the microstructure and transformability of ZrO 2 nanocrystallites in a ZrO 2 -SiO 2 nanocrystalline glass-ceramic (NCGC) during sintering and thermal treatments. The ternary dopants enhanced the transformability of tetragonal ZrO 2 (t-ZrO 2 ) nanocrystallites during sintering, i.e., the dopants acted as t-ZrO 2 destabilizer. The Ta, Nb and Hf elements dissolved in ZrO 2 nanocrystallites, forming ZrO 2 solid solution. Meanwhile, lamella nanotwins were formed within many ZrO 2 nanocrystallites. No obvious segregation of dopants was detected at ZrO 2 grain boundaries. t-ZrO 2 and monoclinic (m) ZrO 2 nanocrystallites were metastable in thermal treatments process, with “t” to “m” and the reverse “m” to “t” polymorphic transformation occurred simultaneously. Meanwhile, t-ZrO 2 and m-ZrO 2 nanocrystallites had a great tendency to grow larger during thermal treatments.