Defect chemistry to trigger zirconia densification at low temperatures by Spark Plasma Sintering

In-depth control of reactivity and defects chemistry is shown to be mandatory to reach high density YSZ ceramics at sintering temperatures lower than 900 degrees C. The combination of Cold Sintering Process (CSP) and Spark Plasma Sintering (SPS) has highlighted the role of transient chemistry on the densification of this material. More, optimised conditions were found for achieving densification of YSZ at 850 degrees C in a one-step SPS process. In particular, the vacuum level in the SPS chamber is clearly shown to be a decisive parameter to obtain dense nanostructured YSZ tetragonal ceramics up to 95% below 900 degrees C. The occurrence of oxygen vacancies has thus been addressed associating thermal analyses, X-ray photoelectron spectroscopy, Electron Paramagnetic Resonance, photoluminescence spectroscopy and impedance spectroscopy. Understanding defect chemistry mechanisms and their dependence on the process or combination of processes, is a lever towards high-quality YSZ nanostructured ceramics below 900 degrees C.