Doping effect of divalent cations on sintering of polycrystalline yttria

The sintering behavior of Y2O3 doped with 1 mol% of Ca2+, Mg2+, Mn2+, Ni2+, Sr2+ or Zn2+ was investigated by pressureless sintering in air at a sintering temperature in the range 900–1600 °C. The sintering temperature required for full densification in Y2O3 was reduced by 100–400 °C by the cation doping, while undoped Y2O3 was densified at 1600 °C. The most effective dopant among the examined cations was Zn2+. The grain growth kinetics of undoped and cation-doped Y2O3 was described by the parabolic law. The grain boundary mobility of Y2O3 was accelerated by doping of the divalent cations. High-resolution transmission electron microscopy (HRTEM) observations and nano-probe X-ray energy dispersive spectroscopy (EDS) analyses confirmed that the dopant cations tended to segregate along the grain boundaries without forming amorphous layers. The improved sinterability of Y2O3 is probably related to the accelerated grain boundary diffusion owing to the grain boundary segregation of the dopant cations.