Abstract
In this work, the electrical conductivities of sputtered 6 nm and 50 nm thick, dense yttria stabilized zirconia (YSZ) thin films are measured using impedance spectroscopy in both dry and humidified air at the intermediate temperatures of 300–650 °C. While the 50 nm thick films exhibited the same conductivity in both dry and humid air, the conductivity of 6 nm thick films in humidified air was around twice as much as that in dry air at temperatures below 500 °C. The conductivity increase for the 6 nm thick film was attributed to surface proton conduction, with a net conductance similar in magnitude to the bulk oxygen ion conductance. Contrary to some literature suggestions, proton conduction is believed to occur along the free surface and not through grain boundaries, since the lateral grain sizes of the 6 nm and 50 nm thick films are comparable. Interestingly, the proton conduction had an activation energy of 1.03 eV, similar to oxygen ion conduction in YSZ.
Highlights
Doped zirconia and ceria are solid electrolyte materials, normally thought to support high oxygen ion conductivity but poor conductivity for all other charged species
Besides oxygen ion and electron/hole conduction, proton conduction has been reported in these solid electrolytes
Wagner[5] suggested that polycrystalline yttria stabilized zirconia (YSZ) is a poor proton conductor based on measurements of the permeation of H2
Summary
Doped zirconia and ceria are solid electrolyte materials, normally thought to support high oxygen ion conductivity but poor conductivity for all other charged species. Scherrer et al and Gregori et al have reported proton conduction in YSZ14 and GDC15 thin lms, respectively, with a thickness of a few hundred nanometers Both of these studies found that a porous lm exhibited proton conduction at temperatures below about 300–400 C, while a dense lm showed no signi cant proton conduction. Paper proton conduction contributes signi cantly to the overall conduction of ultrathin solid oxide electrolyte lms in humid air at intermediate temperatures. This is the rst report of dense YSZ thin lms supporting proton conduction at these temperatures (400–500 C)
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