Proton conductivity of rare-earth oxide–zirconia solid solutions with defect fluorite-type structure.

Proton conductivity in fluorite-structured RE 2 O 3 –ZrO 2 solid solutions (RE = Gd, Sm, and Nd) with the composition of [RE 2 O 3 ]/[ZrO 2 ] ∼ 1 was studied. By screening the proton solubility and diffusivity using the tracer diffusion technique with secondary ion mass spectrometry (SIMS) depth profiling, Nd 0.7 Zr 0.3 O 1.65 was found to exhibit the highest proton conductivity among the prepared RE 2 O 3 –ZrO 2 systems. Detailed electrical conductivity measurements at various atmospheric conditions and temperatures revealed that Nd 0.7 Zr 0.3 O 1.65 is a nearly pure proton conductor below 600 °C under a reducing atmosphere, whereas electron-hole conduction is dominant under an oxidizing atmosphere. The proton conductivity was 1 × 10−4 S cm−1 at 600 °C, which is approximately two orders of magnitude lower than that of Y 2 O 3 -doped BaZrO 3. Because proton solubility in Nd 0.7 Zr 0.3 O 1.65 and Y 2 O 3 -doped BaZrO 3 are similar, the lower conductivity was attributed to the lower proton diffusivity. • H+-conductivity in fluorite-structured RE 2 O 3 –ZrO 2 solid solutions (RE = Gd, Sm, and Nd) was studied. • Nd 0.7 Zr 0.3 O 1.65 is the best H+-conductor among the prepared systems (1 × 10−4 S cm−1 at 600 °C). • Nd 0.7 Zr 0.3 O 1.65 is a nearly pure H+-conductor below 600 °C under a reducing atmosphere. [ABSTRACT FROM AUTHOR]