Polycrystalline ceramic samples of magnesia doped GdSm1–xMgxZr2O7–x/2 have been prepared by conventional solid state reaction method using high purity oxides. The influence of magnesia dopant content on densification, microstructure and electrical properties of GdSm1–xMgxZr2O7–x/2 ceramics are investigated. Magnesia doping promotes the sintering densification behaviour of GdSm1–xMgxZr2O7–x/2 ceramics. GdSm1–xMgxZr2O7–x/2 (x = 0, 0·05, 0·10) ceramics have a single phase of the pyrochlore type structure, while GdSm1–xMgxZr2O7–x/2 (x = 0·15, 0·20) ceramics consist of the pyrochlore type structure and a small amount of magnesia as the second phase. The total conductivity of GdSm1–xMgxZr2O7–x/2 ceramics obeys the Arrhenius relation, and gradually increases with increasing temperature from 723 to 1173 K. GdSm1–xMgxZr2O7–x/2 ceramics are oxide-ion conductors in the oxygen partial pressure range of 1·0×10–4 to 1·0 atm at each test temperature. The maximum value of the total conductivity is 1·29×10–2 S cm–1 at 1173 K for the GdSm0·85Mg0·15Zr2O6·925 ceramic.
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