Effect of Dopants on Zirconia Stabilization—An X‐ray Absorption Study: II, Tetravalent Dopants

Abstract

X‐ray absorption spectra at Zr‐ K , Ce‐L 111 and Ge‐ K edges in ZrO 2 –CeO 2 and ZrO 2 –GeO 2 solid solutions have been measured at 10 K. Both Ce and Ge substitute for Zr in the cation network, but CeO 8 and GeO 4 polyhedra are maintained around the dopants. The oversized CeO 8 is compressed to a Ce–O distance of 2.30 Å, which is smaller than the 2.35 Å seen in fluorite‐type CeO 2 . Meanwhile, the distortion of the Zr‐cation network is increased and the tetragonality is reduced. The undersized Ge has a Ge–O distance of 1.80 Å, which is much shorter than the Zr–O, distance of 2.10 Å. A strong tendency for Ge–Zr ordering in tetragonal solid solutions into locally scheelite‐like clusters, even within the solubility limit, is observed. This results in an increase in the tetragonality and a decrease in the distortion of the cation network. Despite the opposite effects on tetragonality, both Ce and Ge doping can stabilize tetragonal zirconia albeit via different mechanisms. The structural origin of the cubic phase is also elucidated.