Effective Ionic Radius of Y 3+ Determined from Lattice Parameters of Fluorite‐Type HfO 2 and ZrO 2 Solid Solutions

Fluorite type HfO 2 and ZrO 2 solid solutions were prepared by doping with 8 to 14 mol% of Ho 2 O 3 and Y 2 O 3 , and their lattice parameters were determined. In both HfO 2 and ZrO 2 systems, the lattice parameters of the solid solutions containing Ho 2 0 3 were consistently greater than those containing the same amounts of Y 2 O 3 . This indicated that the ionic radius of Ho 3+ was larger than that of Y 3+ in the fluorite structure solid solutions. The effective ionic radius of Y 3+ in eightfold coordination was estimated to be 0.1011 nm by using the measured lattice parameters and the empirical equations to predict the lattice parameters of the fluorite‐type solid solutions.