Effect of NiO-to-Ni transformation on conductivity and structure of yttria-stabilized ZrO2

The conductivity and structure of 8-mol%-yttria-stabilized zirconia with ad ditions of nickel oxide has been investigated, both in the as-prepared stat e and after reduction of NiO in hydrogen. During reduction at 1000 degreesC , the conductivity decreases by 40%-50% and most of the NiO dissolved in th e zirconia is exsolved in the form of nickel particles. This is accompanied by the formation of tetragonal zirconia precipitates of size 10-40 nm and by an increase in the lattice parameter. On reoxidation in air at 1000 degr eesC, the change in lattice parameter is partly reversed, but the conductiv ity shows no further changes.