A computational study of yttria-stabilized zirconia: I. Using crystal chemistry to search for the ground state on a glassy energy landscape

Abstract

Yttria-stabilized zirconia (YSZ), a ZrO2-Y2O3 solid solution that contains a large population of oxygen vacancies, is widely used in energy and industrial applications.Past computational studies correctly predicted the anion diffusivity but not the cation diffusivity, which is important for material processing and stability. One of the challenges lies in identifying a plausible configuration akin to the ground state in a glassy landscape. This is unlikely to come from random sampling of even a very large sample space, but the odds are much improved by incorporating packing preferences revealed by a modest sized configurational library established from empirical potential calculations. Ab initio calculations corroborated these preferences, which prove remarkably robust extending to the fifth cation-oxygen shell about 8 Å away.2 Yet because of frustration there are still rampant violations of packing preferences and charge neutrality in the ground state, and the approach toward it bears a close analogy to glass relaxations. Fast relaxations proceed by fast oxygen movement around cations, while slow relaxations require slow cation diffusion. The latter is necessarily cooperative because of strong coupling imposed by the long-range packing preferences.

A computational study of yttria-stabilized zirconia: II. Cation diffusion

“…This is demonstrated by Fig. 9c, (correlation factor: 0.78) in which the Buckingham potential in the empirical potential [14,19] was used to calculate the short-range repulsions between the migrating Zr and nearby oxygens up to 3 Å. It is a reasonable result since the less repulsion the neighboring ions exert on the migrating cation, the less migration barrier the migrating ion should experience.…”

“…This study will address the above need. As we already noted in the companion paper (hereafter referred to as Paper I) [14], all the previous computational studies on cation defect and diffusion in YSZ employed empirical potential calculations [9][10][11][12][13]15]. This is not surprising because YSZ contains not only two types of cations but also many anion vacancies, which generate an astronomically large number of configurations even for a small supercell.…”

Electrical and hydrogen reduction enhances kinetics in doped zirconia and ceria: II. Mapping electrode polarization and vacancy condensation in YSZ

“…4.5 | Flash sintering in air and graded microstructure Enhanced cathodic grain growth has been observed in flash sintered 3YSZ. Instead, any modification of grain growth kinetics must come via the polarization of the chemical potential of the rate controlling species, e.g., cations in zirconia, 39,40 because of inadequate electrode kinetics. (We estimated current density using the geometry of the green body, which has a packing density~50%; if we estimate it using the geometry of the sintered body, which has full density, then the current density is~17 A/cm 2 ).…”

“…Therefore, grain growth of isotropic materials cannot be directly caused by an electric field. Instead, any modification of grain growth kinetics must come via the polarization of the chemical potential of the rate controlling species, e.g., cations in zirconia, 39,40 because of inadequate electrode kinetics. As will become clear in the Appendix, the chemical potential of cation is fully determined once the oxygen potential is known.…”

DC electrical degradation of YSZ: Voltage‐controlled electrical metallization of a fast ion conducting insulator

“…Charge neutrality, a large band gap, and disparate formation energies of different lattice defects rather strictly define the stoichiometry of insulating 8YSZ . Therefore, pumping out more oxygen than letting into it unavoidably renders it unstable, decomposing into a suboxide starting at the cathode.…”