Effects of oxygen vacancy on bond ionicity, lattice energy, and microwave dielectric properties of CeO₂ ceramics with Yb³⁺ substitution

Novel Yb_xCe_1−xO_2−0.5x (x = 0–0.8) ceramics, designed by replacing Ce⁴⁺ with Yb³⁺ ions were prepared by conventional oxide reaction, and the structural stability of the cubic fluorite structure was assessed using lattice energy and ionic properties of Ce/Yb–O bonds. The oxygen vacancy caused by unequal substitution, which played a decisive role in bond ionicity and lattice energy, was analyzed experimentally by XPS and also theoretically by first principles. The Yb_xCe_1−xO_2−0.5x ceramics maintain a stable cubic fluorite structure when x ≤ 0.47, corresponding to the minimum lattice energy of 4142 kJ/mol with the lowest ionicity as ƒ_i = 87.57%. For microwave dielectric properties, when the Yb_xCe_1−xO_2−0.5x (x = 0–0.4) ceramics are pure phase, the porosity-corrected permittivity is dependent on the bond ionicity. The Q׃ values are related to the lattice energy and grain distribution. The temperature coefficient of resonance frequency has been analyzed using bond valence. When the Yb_xCe_1−xO_2−0.5x (x = 0.5–0.8) ceramics are multiple phases, the microwave dielectric properties are associated with the phase composition and grain growth.