Conductivity and thermal expansion of the Ce0.8Gd0.2O1.9 solid electrolyte in the oxidizing and reducing atmospheres

Abstract

Highly compact (99%) solid electrolyte Ce0.8Gd0.2O1.9 with submicron (0.3 μm) grains is synthesized. The dilatometric (20–850°C) and conductivity (180–350°C) measurements are performed on the electrolyte in air and as a function of the partial oxygen pressure $$p_{O_2 } $$ (0.21−1×10−25 atm) at 600, 700, and 800°C. An inflection is found in the temperature dependences of the thermal coefficient of linear expansion and conductivity (impedance measurements) at ∼230°C, which is the evidence for a phase transition. The activation energies for conduction in the grain bulk and boundaries differ only slightly, indicating that the grain boundaries’ resistance is caused not by the precipitation of the second phase at the boundaries, but most probably by the presence of intergranular nanopores. The dilatometric measurements confirm a significant increase in the linear dimensions of Ce0.8Gd0.2O1.9 in the reducing atmospheres with a parallel increase in its electron conductivity. The electron conductivity and specific elongation increase proportionally to $$p_{O_2 }^{ - 1/4} $$ at all temperatures. The $$p_{O_2 } $$ values, at which the transport numbers of ions t i = 0.5, are determined. They are 10−22.5, 10−20, and 10−18 atm at 600, 700, and 800°C, respectively.