HEO ceramics for detecting the ionic conductivity component in electron conductors

A series of solid solutions with high content of Tb2O3 — (TbxTi1–x)4O8–2x (x = 0.667–0.83) have been synthesized in the Tb2O3–TiO2 system by the method of co-precipitation and/or mechanical activation followed by high temperature annealing for 4–22 h. The X-ray diffraction method showed that the fluorite structure is realized for (TbxTi1–x)4O8–2x (x = 0.75–0.817). The solid solution Tb3.12Ti0.88O6.44 (64 mol.% Tb2O3 (x = 0.78)) with a fluorite structure was found to have a maximum hole conductivity of ~ 22 S/cm at 600 °C. In order to separate the ionic component of the conductivity in the electronic conductor Tb3.12Ti0.88O6.44, its high entropy analogue, (La0.2Gd0.2Tm0.2Lu0.2Y0.2)3.12Ti0.88O6.44, was synthesized in which all RE cations have a valency of 3+. As a result, the contribution of ionic (proton) conductivity (~ 7×10−6 S/cm at 600 °C) was revealed against the background of dominant hole conductivity. The proton conductivity of HEО (La0.2Gd0.2Tm0.2Lu0.2Y0.2)3.12Ti0.88O6.44 is confirmed by the detection of the isotope effect, where the mobility of the heavier O-D ions is lower than that of the O-H hydroxyls, resulting in lower conductivity in D2O vapors compared to H2O.