Introductory Remarks

Yttria-stabilized zirconia (YSZ) is the most-common electrolyte material for solid oxide fuel cells due to its reasonable oxygen-ion conductivity and chemical stability. To achieve suitable ionic conductivities, YSZ ceramics must be near theoretical density, requiring sintering temperatures around 1450°C. Alternatively, flash sintering has been shown to densify YSZ ceramics at ~750°C in just a few seconds. During flash sintering, an electric field is applied across the sample and once a threshold temperature is reached, the sample conductivity and power dissipation rapidly increase causing densification. Since densification occurs quickly, grain growth can be difficult to control. The addition of a small amount of aluminum oxide (Al₂O₃) has been shown to hinder grain growth, enhance densification, and increase YSZ ionic conductivity during conventional sintering. Typically, secondary phase particles (Al₂O₃) are added to primary ceramic particles (YSZ) by mechanical mixing which can lead inhomogeneities in the final microstructure. In this work, particle atomic layer deposition (ALD) was used to conformally coat each YSZ particle with a thin film of amorphous Al₂O₃, homogeneously dispersing the Al₂O₃ prior to flash sintering. Transmission electron microscopy and scanning electron microscopy were used to characterize the as-deposited Al₂O₃ films and to determine the effect of the Al₂O₃ films on grain growth and microstructural homogeneity. Density measurements showed that a small amount of amorphous Al₂O₃ added by particle ALD increased the final density of YSZ after flash sintering. Particle ALD homogeneously adds amorphous Al₂O₃ to YSZ particles, resulting in higher final densities and greater microstructural control to enhance properties of interest (mechanical strength, ionic conductivity, etc.) after flash sintering.