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Non-stoichiometric perovskite oxides are a versatile class of functional ceramics. Their ABO3 framework accommodates many different cations and tolerates large changes in oxygen content, captured by the non-stoichiometry parameter δ. At high temperature and low oxygen partial pressure (pO2), oxygen vacancies are formed and B-site cations are reduced for charge neutrality. My research follows a single idea: oxygen content, usually adjusted to tune functional properties, can also serve as an active processing variable. I chose PrBaMn2O6 (PBMO) as a model system, since it remains structurally stable despite a high oxygen vacancy concentration — an ideal platform for studying how oxygen content can be used to control ceramic processing.

The first part introduces atmosphere as a new lever on the sintering of non-stoichiometric perovskites. Its outcome has long been governed by just two variables, time (t) and temperature (T); in these oxides, I found that atmosphere (pO2) can act as a comparably powerful third one. Specifically, I observed that introducing oxygen vacancies in PBMO significantly accelerates its sintering: for example, annealing at 900 °C under a reducing atmosphere gives a degree of coarsening comparable to that reached at 1200 °C in air. I attributed this to vacancy-induced bond softening, which lowers the barrier to atomic transport. Notably, this stays within the oxide regime — unlike oxide-to-metal reduction — and is reversible on demand. Sintering at a much lower temperature reduces the required energy and the carbon footprint, while broadening the available processing window. Currently, I am extending this to other perovskites.

The second part addresses constrained sintering, a classic problem in multilayer ceramics. As adjacent layers shrink by different amounts — most severely when a film is sintered on a rigid substrate — the mismatch drives stress and failure. Here I exploit a behavior particular to non-stoichiometric perovskites: as oxygen non-stoichiometry develops, the cations are reduced, and the lattice expands — counter to the intuition that losing oxygen should shrink it. In PBMO, I turn this into a processing route: starting from oxidized powder, I pack the green body on a rigid substrate and then sinter it in a reducing atmosphere, so that the non-stoichiometry induced in situ expands the lattice and offsets the shrinkage of sintering — an approach I termed Nonstoichiometric-Expansion-Compensated Constrained Sintering (NECCS).

By combining the two — the lower sintering temperature that lets PBMO be co-fired with a metal support, and NECCS that suppresses constraint-driven cracking — I formed a crack-free porous PBMO electrode directly on a rigid metal support, with pores and surface roughness fine enough to support a dense thin-film electrolyte. This forms the basis for a metal-supported thin-film solid oxide fuel cell (TF-SOFC) with a perovskite anode, which I am now developing.

Jaewon Yoo

Seoul National University / Mechanical Engineering Department / Renewable Energy Conversion Laboratory, Republic of Korea

jw0325@snu.ac.kr

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