Effects of oxygen vacancy on bond ionicity, lattice energy, and microwave dielectric properties of CeO <sub>2</sub> ceramics with Yb <sup>3+</sup> substitution
Ming‐An Shi, Shuyang Ma, Wangsuo Xia, Ying Wang, Jinzi Yu, Haitao Wu
Abstract
Novel Yb<sub><i>x</i></sub>Ce<sub>1−<i>x</i></sub>O<sub>2−0.5<i>x</i></sub> (<i>x</i> = 0–0.8) ceramics, designed by replacing Ce<sup>4+</sup> with Yb<sup>3+</sup> 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<sub><i>x</i></sub>Ce<sub>1−<i>x</i></sub>O<sub>2−0.5<i>x</i></sub> ceramics maintain a stable cubic fluorite structure when <i>x</i> ≤ 0.47, corresponding to the minimum lattice energy of 4142 kJ/mol with the lowest ionicity as ƒ<sub>i</sub> = 87.57%. For microwave dielectric properties, when the Yb<sub><i>x</i></sub>Ce<sub>1−<i>x</i></sub>O<sub>2−0.5<i>x</i></sub> (<i>x</i> = 0–0.4) ceramics are pure phase, the porosity-corrected permittivity is dependent on the bond ionicity. The <i>Q</i>׃ 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<sub><i>x</i></sub>Ce<sub>1−<i>x</i></sub>O<sub>2−0.5<i>x</i></sub> (<i>x</i> = 0.5–0.8) ceramics are multiple phases, the microwave dielectric properties are associated with the phase composition and grain growth.