1at%Mn was introduced to highly pure (~30ppm SiO2) and impure (~500ppm

SiO2) 8YSZ electrolytes via a wet chemical method. The densification behaviour, sintering mechanism and ionic conductivity of the two groups of samples were

systematically investigated. The addition of 1at%Mn enhanced the densification

and promoted grain growth of both pure and impure samples, which was attributed

to the fact that the presence of Mn significantly reduced the apparent activation

energy, although it did not change the early-stage sintering mechanism (dominated

by volume-diffusion). The addition of Mn decreased the grain interior conductivity,

with almost little impact on the grain-boundary conduction for the pure samples.

However, the combination of silica (a contaminant in impure 8YSZ) with Mn led

to a significant deterioration to the grain-boundary effect compared with silica

alone. Based on the estimated activation energies for grain-boundary conduction, it

was found that the “constriction model” can be used to describe the grain-boundary

behaviours of the samples more appropriately than other models. The grainboundary

coverage fraction decreased with increasing sintering temperature,

leading to a continuous increase in the GB conduction, which was found to be

associated with the dissolution of silica into zirconia lattice during sintering at high

temperatures.

Effect of Mn Addition on the Densification, Grain Growth and Ionic Conductivity

of Pure and SiO2-Containing 8YSZ Electrolytes. T.S.Zhang, S.H.Chan, W.Wang,

K.Hbaieb, L.B.Kong, J.Ma: Solid State Ionics, 2009, 180[1], 82-9