Relative Occurrence of Oxygen-Vacancy Pairs in Yttrium-Containing Environments of Y₂O₃-Doped ZrO₂ Can Be Crucial to Ionic Conductivity

Abstract

Yttria-stabilized zirconia (YSZ) is widely used as an electrolyte in solid oxide fuel cells. Much of current research on ionic conductivity in YSZ has focused on understanding migration barriers for O2– ion movement and vacancy trapping behavior in an attempt to understand why dopant cation edges result in fewer vacancy hopping transitions. We show that the free energy of finding O2–-vacancy (O2–-vac) pairs in a local environment can also be crucial to the hopping transitions. Higher probability of O2–-vac pairs can result in a greater number of transitions. O2– ion movement in bulk YSZ is studied here using multiple independent short molecular dynamics (MD) trajectories. Analysis of the MD trajectories yields free energy of O2–-vac pairs in 42 different local cation (Y3+/Zr4+) environments, to our knowledge calculated for the first time, as well as coarse-grained O2– hopping rates and Arrhenius parameters. On the basis of the free energies we conclude that it is possible that ionic movement is hindered in some environments not only because of high migration barriers or vacancy trapping as believed earlier but also because O2–-vac pairs are destabilized by these environments. Increasing the temperature and/or decreasing the dopant composition stabilizes O2–-vac pairs in these environments, which in turn affects the YSZ conductivity. Another newly found aspect is the connection between the kinetic rate constants for different environments; namely, the rates of interconversion between two environments depend on their O2–-vac free energy differences.

All‐Solid‐State Oxygen Ion Electrochemical Random‐Access Memory for Neuromorphic Computing

“…Oxygen vacancies incorporated in the ZrO 2 www.advelectronicmat.de lattice provide high O 2ion conductivity. [25] Depositing YSZ in an oxygen-rich environment may compensate for lattice oxygen vacancy, which affects the YSZ conductivity and switching characteristics of the O-ECRAM device. This hypothesis was further supported by the changes in the O1s spectra of YSZ-I, YSZ-II, and YSZ-III.…”

Resolving the Temperature and Composition Dependence of Ion Conductivity for Yttria-Stabilized Zirconia from Machine Learning Simulation

“…Yttria-stabilized zirconia (YSZ, Y 2 x Zr 1–2 x O 2– x ) is one of the most important ion conducting solids, widely used in solid oxide fuel cells (SOFCs), solid oxide electrolysis cells (SOECs), and oxygen sensors. − Chemically, the ion conduction in YSZ can be understood as the consequence of the motion of oxygen vacancies (O v ) that are present due to the charge balance required by doped Y 3+ cations to replace Zr 4+ . The ever-increasing observations on the measured conductivity from experiments are, however, far more intriguing than one’s expectation.…”

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“…Zirconium oxides and hydroxides are inorganic compounds of major scientific and industrial importance. One of the prime examples is yttria-stabilized zirconia, which has been extremely well studied due to its excellent ionic conduction and mechanical properties. − ZrO 2 has also more recently been attracting a great deal of attention as a possible replacement for SiO 2 in complementary metal-oxide-semiconductor devices, as its higher dielectric constant permits the creation of thinner layers. − Many studies have also looked at ZrO 2 as a potential catalyst for the breakdown of species such as CO. , …”