Effect of Nb 2 O 5 Alloying on Thermal Expansion Anisotropy of 2 mol% Y 2 O 3 ‐Stabilized Tetragonal ZrO 2

Tetragonal ZrO 2 ( t ‐ZrO 2 ) solid solutions were prepared with addit ons of 2 mol% Y 2 O 3 plus up to 0.45 mol% Nb 2 O 5 . The thermal expansion coefficients in both the a‐ and c ‐axis lattice directions increased with Nb 2 O 5 alloying and the thermal expansion in the c ‐axis direction was greater than that in the a ‐axis direction over the entire composition range. This anisotropic thermal expansion behavior was related to the 4‐fold coordination of Nb 5+ with oxygen ions in t ‐ZrO 2 solid solutions in the system ZrO 2 –Y 2 O 3 –Nb 2 O 5 . The fracture toughness continuously increased with Nb 2 O 5 alloying and suggested that the c/a axial ratio is a more significant factor than the internal stress that arises from the thermal expansion anisotropy, in the determination of the transformability of t ‐ZrO 2 in this system.