The effects of sintering temperature and addition of 4 mol.% ZnO as sintering additive on the crystal structure, microstructure and electrical properties of SrZr0.9Y0.1O3-delta are reported. The presence of ZnO as sintering aid brings about high densification at 1300 degrees C (relative density similar to 97%); gas-tightness is not achieved for ZnO-free samples sintered below 1600 degrees C. Bulk conductivity (sigma(B)) is considerably higher in wet and dry O-2 on doping with ZnO, but only slight variations of sigma(B) with sintering temperature are observed for the Zn-containing phases. Similarly, the apparent grain-boundary conductivities are much greater for the Zn-doped samples. The grain-boundary volume and accompanying resistances are much reduced on sintering at 1500 degrees C with ZnO addition in comparison to Zn-modified samples sintered below 1500 C-degrees, with only minor changes in grain-boundary relaxation frequency observed. Conversely, in comparison to the undoped sample with sintering temperature of 1600 C-degrees, there is an enormous improvement in the specific grain-boundary conductivity of two orders of magnitude for the ZnO-containing samples. Analysis on the basis of the core space-charge-layer model relates the enhancement of the grain-boundary transport to a higher concentration of charge carriers in the space-charge layer and associated lower potential barrier heights. (C) 2016 Elsevier B.V. All rights reserved.