Grain boundary segregation-induced phase transformation and grain growth in Y₂O₃-stabilized ZrO₂ polycrystals

We systematically investigated the phase- Transformation and grain-growth behaviors during sintering in 2 and 3 mol% Y₂O₃-stabilized tetragonal ZrO₂ (2Y and 3Y) and 8 mol% Y₂O ₃-stabilized cubic ZrO₂ polycrystals (8Y). In particular, grain-boundary segregation and grain-interior distribution of Y³⁺ ions were examined by high-resolution transmission electron microscopy (HRTEM)- And scanning transmission electron microscopy (STEM)-nanoprobe X-ray energy dispersive spectroscopy (EDS) techniques. Above 1200°C, grain growth during sintering in 8Y was much faster than that in 2Y and 3Y. In the grain boundaries in these specimens, amorphous layers did not present; however, Y³⁺ ions segregated at the grain boundaries over a width of about 10 nm. The amount of segregated Y³⁺ ions in 8Y was significantly less than in 2Y and 3Y. This indicates that the amount of segregated Y³⁺ ions is related to grain growth behavior; i.e., an increase in segregated Y³⁺ ions retards grain growth. Therefore, grain-growth behavior during sintering can be reasonably explained by the solute-drag mechanism of Y³⁺ ions segregating along the grain boundary. In 2Y and 3Y, the cubic-phase regions were formed in grain interiors adjacent to the grain boundaries and/or the multiple junctions in which Y³⁺ ions segregated, which can be explained by a grain boundary segregation-induced phase transformation (GBSIPT) mechanism.