Meaning
Presence of partially reduced, non-stoichiometric oxide species in a ceramic material after high-temperature thermal processing. In solid-state electrolyte fabrication, suboxide retention occurs when the sintering environment or rapid thermal cycle prevents the full oxidation of metal ions to their highest oxidation state. This phenomenon modifies the optical, electrical and mechanical characteristics of the sintered body.
Minimizing this effect is a primary target in producing highly resistive separators.
Secondary Phase
These reduced species often concentrate at the grain boundaries or along the pore surfaces. The presence of such suboxide retention phases alters the local chemical potential and increases the sensitivity of the ceramic to moisture and ambient carbon dioxide. Preventing their formation ensures stable long-term contact with metallic anodes.
Sintering Atmosphere
Control of the oxygen concentration during heat treatment determines the thermodynamic stability of the various metal oxides. Insufficient oxygen during rapid cooling steps leads to suboxide retention, whereas a post-sintering anneal in air can help convert these suboxides back to the desired stoichiometric phases.
Electronic Conduction
Low-valency metal species can introduce localized electronic states in the band gap, promoting unwanted electronic conductivity. This electronic transport in a solid electrolyte increases self-discharge rates and can trigger internal short circuits during battery charging.
