Oxygen sensitive double layered CeO 2/Nb 2O 5 films were grown on Al 2O 3 ceramic substrates by reactive RF/DC magnetron sputtering.The CeO 2/Nb 2O 5 double layered films were studied by X ray photoelectron spectroscopy to understand the interfacial diffusion after in situ thermal annealing.Our interesting finding is that the thermal diffusion of Nb 2O 5 into the top CeO 2 layers results in two favorable results.For one thing,trace doping of Nb 2O 5 into the top CeO 2 layers can be reali...