Abstract

Solute segregation at grain boundaries has been correlated with grain‐boundary conductivity in high‐purity 15‐mol%‐CaO‐stabilized ZrO 2 . STEM measurements of solute coverage show that the segregation of impurity silicon (present at bulk levels <80 ppm) is grain‐size dependent. The boundary coverage of silicon can be systematically varied by varying grain size at concentrations low enough that a discrete siliceous film does not form. The cosegregation of calcium and silicon is observed. The grain‐boundary solute coverage (T si+Ca ) has been correlated with the specific grain‐boundary conductivity (σ sp gb ) determined using impedance spectroscopy. At monolayer segregation levels, the specific boundary conductivity is less than the bulk conductivity by a factor >10 3 at 500°C. At the lowest levels of segregation achieved, <0.1 monolayer, σ sp gb remains ∼10 2 less, and possibly represents an “intrinsic” limiting value for the grain boundary. Comparison with Y 2 O 3 ‐doped ZrO 2 suggests similar behavior in this system. The control of grain‐boundary segregation through purity, microstructure, and thermal history is discussed from the objective of engineering the grain‐boundary impedance of polycrystalline ionic conductors.