Nanosized ceria-based ceramics: a comparative study

Ce_(1−x)Gd/Sm _x O_2−δ (x = 0.05–0.2, GDC/SDC) nanometric powder was prepared by glycine-nitrates combustion synthesis, by strictly following uniformity in the preparation route. The thermochemical properties of the obtained precursor were studied by TGA/DTA. Crystallization of the fluorite phase occurred on heating at 800 °C or higher temperature. The grain size of calcined powder was found to be about 15 nm. Densification was studied as a function of dopant content. SDC was found more sinterable than GDC. Crystal structure and microstructure were characterized by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). Electrical characterization was carried out using the impedance spectroscopy method in the frequency range of 50 Hz–13 MHz. The bulk conductivity of SDC is higher than GDC pellet for all concentration ranges. The results were analyzed by using the concept of change of the chemical bond ionicity due to the replacement of the host by dopant. Guest/host ionic size, valence mismatch ratio and their consequences are counted semiquantitatively into the configurational and thermal entropy.