X-ray and electrical conductivity study of the fluorite phase in the system ZrO₂-CaO

Abstract

In the ZrO₂-CaO system cubic solid solutions of the fluorite-type structure are formed between 12 and 22 mole % CaO for specimens fired at 2000°C and subsequently quenched from 1400°C. The lattice parameter increased linearly from 5.125 to 5.144 Å with increasing CaO content. Results of x-ray diffraction intensity studies favored the oxygen-ion vacancy model over the cation interstitial model for these solid solutions. As the CaO content was increased from 13 to 20 mole %, the electrical conductivity at 1000°C decreased from 5×10^-2 to 6×10^-3 Ω^-1 cm^-1 and the activation energy increased from 1.11 to 1.35 eV. Specimens heated at 1000°C for one week showed extra x-ray diffraction lines. These data coupled with accompanying changes in electrical conductivity are discussed in terms of an order- disorder transition.