Densification and grain growth of SiO2-doped ZnO

The grain growth kinetics in the 1, 2, 3 and 4 wt.% SiO2 doped ZnO was studied using the simplified phenomenological grain growth kinetics equation Gn−G0n=K0texp(−Q/RT) together with microstructure properties and densification of the sintered samples. The grain growth exponent values (n) were found to be 3 for 1 wt.% SiO2 doped ZnO, 6 for 2 and 3 wt.% SiO2 doped ZnO and 7 for 4 wt.% SiO2 doped ZnO. The apparent activation energy of 486 kJ/mol was found for 1 wt.% SiO2 added system. A sharp increase in the apparent activation energy to a value of 900, 840 and 935 kJ/mol was found for 2, 3 and 4 wt.% SiO2 added system, respectively. The apparent activation energy was increased with doping of SiO2 because of the formation of spinel Zn2SiO4 phase at the grain boundaries. This spinel phase inhibited the grain growth of ZnO. Also densification decreased with increasing SiO2 doping.