Beneficial Lattice Strain in Heterogeneously Doped Ceria

Oxygen ion conduction in heterogeneously doped films composed of alternating layers of pure Y2O3 and pure CeO2 was reported recently, with conduction coming predominantly from vacancies trapped in interfacial space charge regions in CeO2. Here, we expand this concept to films composed of CeO2 heterogeneously doped with Y2O3, Gd2O3, or La2O3 in order to study the effects of heterodopant identity on the oxygen ion conductivity. For all samples, the thickness of the entire structure and that of the individual dopant layers were kept constant. The dopant oxides used in this work adopt the cubic bixbyite crystal structure with pseudo-fluorite lattice parameters that are, relative to CeO2, smaller (Y2O3), larger (La2O3), and nearly equal (Gd2O3). The total conductivity of the films increased with increasing lattice parameter of the dopant oxides. An electrostatic Gouy–Chapman model is not sufficient to explain this behavior because all of the dopants theoretically contribute identical interfacial oxygen vacancy concentrations. Therefore, extensions beyond a Gouy–Chapman model are suggested, with consideration for the effects of interfacial strain on the concentration and mobility of vacancies from dopant oxides in the space charge region.