Lattice Parameters, Ionic Conductivities, and Solubility Limits in Fluorite‐Structure MO ₂ Oxide [M = Hf ⁴⁺ , Zr ⁴⁺ , Ce ⁴⁺ , Th ⁴⁺ , U ⁴⁺ ] Solid Solutions

Changes in the lattice parameters of fluorite type MO 2 oxides (M = Hf 4+ , Zr 4+ , Ce 4+ , Th 4+ , U 4+ ) due to the formation of solid solutions can be predicted by proposed empirical equations. The equations show the generalized relationship between dopant size and ionic conductivity in the binary systems of these oxides, illustrating that the smaller the difference between the dopant ionic radius and the critical dopant radius, the higher the conductivity. The solubility limit of the same periodic group elements in fluorite‐structure MO 2 oxides decreaes linearly with the square of Vegard's slope for each solute as determined from the proposed equations.