The temperature dependence of the relative grain‐boundary energy of yttria‐doped alumina

Atomic force microscopy was used to measure the dimensions of grain‐boundary thermal grooves on the surfaces of Al₂O₃, 100 ppm Y‐doped Al₂O₃, and 500 ppm Y‐doped Al₂O₃ ceramics heated at temperatures between 1350°C and 1650°C. The measurements were used to estimate the relative grain‐boundary energies as a function of temperature. The relative grain‐boundary energies of Al₂O₃ decrease slightly with increased temperature. When the doped samples were heated, there was an overall increase in the grain‐boundary energy, attributed to a reduction in the grain boundary excess at higher temperature. The overall trend of increasing grain‐boundary energy was interrupted by abrupt reductions in grain‐boundary energy between 1450°C and 1550°C. In the same temperature range, there is an abrupt increase in the grain‐boundary mobility that is associated with a complexion transition. When the 100 ppm Y‐doped sample was cooled, there was a corresponding increase in the relative grain‐boundary energy at the same complexion transition temperature, indicating that the transition is reversible.