Influence of through-lamella grain growth on ionic conductivity of plasma-sprayed yttria-stabilized zirconia as an electrolyte in solid oxide fuel cells

The development of a cost-effective fabrication method for stabilized zirconia electrolyte for the most advanced tubular solid oxide fuel cell (SOFC) remains the most important challenge for the commercialization of an SOFC power generation system. Atmospheric plasma spraying is expected to be a promising alternative to other costly electrolyte processing methods. The problem with the plasma-sprayed ceramic coating is the limited interface bonding of the lamellar structure, which reduces the ionic conductivity of stabilized zirconia deposits to one-fifth of the comparable bulk. Continuous growth of columnar grains across splat–splat interfaces has been achieved through control of the substrate surface temperature which affects spreading of molten droplets. These cross-splats columnar grains lead to improved bonding between lamellae. Measurements over the temperature range of 600–1000 °C have shown that the microstructural changes result in a significant increase of ionic conductivity of the yttria-stabilized zirconia deposit (by a factor of about 3). A change in activation energy at about 750 °C was observed for coatings deposited with two different sets of spray conditions. This change is associated with a switch of the predominant ion conduction path from grain boundary to intragrain with increasing temperature.