Effects of synthesis conditions on the nanostructure of Ce_xZr_1-xO₂ mesoporous ceramics

From X-ray diffraction (XRD) results it could be concluded that the two proposed syntheses produce a solid solution of Ce_xZr_1-xO₂ crystallized in a two phase system: cubic (space group Fm-3m) and tetragonal (P4₂/nmc). Synthesis A also generates a non-dissolute phase in ceria (ZrO₂), which is a tetragonal phase with space group P4₂/nmc. The synthesis B has a higher density, larger crystallite size and greater amount of cubic phase. The two syntheses present a non-uniform particle size distribution with the exception of sample Ce90B. Notwithstanding different pH values used in syntheses B the crystal phases did not change, but there are other differences in crystal structure like cell parameters, density and crystallite size. All materials exhibit a type IV isotherm and type H4 of hysteresis loop, indicating a mesoporous structure with narrow slit like pores. Synthesis A possesses a higher specific surface area and a larger pore volume. On the other hand, synthesis B exhibits a larger pore diameter. The Brunauer-Emmet-Teller (BET) specific surface areas and pore volume increase with the increase in pH values. The average pore diameters are affected by pH values. It is possible to notice a tendency of increase specific surface area and pore diameter with increase in the amount of ceria content for both syntheses. Through pore size distribution, all samples have a greater concentration of pore size in mesoporous range. Nevertheless, there is a presence of micropores in all samples. (author)