Doping effect on sinterability of polycrystalline yttria: From the viewpoint of cation diffusivity

The sintering behavior of Y2O3 doped with 1 mol% of a trivalent or tetravalent cation was investigated by pressureless sintering in air. Ga3+ or Ge4+-doped Y2O3 bodies exhibited higher relative densities than the undoped Y2O3, while the La3+ or Zr4+-doping suppressed the densification of Y2O3. An interdiffusion experiment was performed on the diffusion couples of polycrystalline Er2O3 and Y2O3 doped with Ni2+ or Zr4+, which are some of the most effective and least effective dopants for the improvement of the sinterability, respectively. The lattice and grain boundary diffusion coefficients of the Er3+ cation in Y2O3 were increased by the Ni2+-doping, but were decreased by the Zr4+-doping. High-resolution transmission electron microscopy observations and nano-probe X-ray energy dispersive spectroscopy analyses confirmed that the dopant cations segregate along the grain boundaries without forming an amorphous phase. The doping effect on the sinterability of Y2O3 must result from the change in the diffusivity in Y2O3.