Electrochemical reduction-induced phase transformation and lattice modification in cubic zirconia (8YSZ)

Abstract

This study investigates the effects of electrical loading on cubic 8YSZ (8 mol% yttria-stabilized zirconia) under different atmospheric conditions with a focus on electrical and structural changes, lattice modifications, and the formation of new phases. Upon applying an electric field during various atmospheric transitions from oxygen to air to argon or nitrogen, an increase in oxygen extraction and enhanced electrical conductivity was linked to the formation of an atmosphere-dependent defective FCC rocksalt phase, ZrO in Ar, and Zr(O,N) in nitrogen, as confirmed by EDS, X-ray diffraction, and Raman spectroscopy, with lattice parameters consistent at approximately 0.458 nm. The microstructure of the electrically loaded material showed elongated precipitates of this new phase, particularly along grain boundaries, which were a few tens to hundreds of nanometers in size. Furthermore, dopant segregation and microstructural instability due to this lattice modification and phase transformation were observed. Comparison to the behavior of tetragonal 3YSZ revealed significant differences between the two compositions. These findings highlight the role of electrochemical reduction in altering material properties, with potential implications for flash sintering and energy applications like solid oxide fuel and electrolyzer cells.