Oxygen stoichiometry control of nanometric oxide compounds: The case of titanium ferrites

Three techniques have been coupled with an original device, based on H2/H2O equilibrium, controlling oxygen partial pressure: XRD, TGA and DC conductivity in order to characterize very reactive compounds such as nanometric powders. From XRD, both the structure and the oxygen stoichiometry (thanks to their lattice parameter) were investigated in situ. From TGA, it was the oxygen stoichiometry (thanks to mass gain or loss) which was determined. From DC conductivity, it was both the structure and the oxygen stoichiometry (thanks to the activation energy) which were obtained. The advantages were to determine very rapidly and with a small amount of powder the equilibrium conditions (T, pO2) necessary to obtain the desired phase and stoichiometry. These methods have been evaluated for nanometric titanium ferrites. Two phenomena have been observed during the reducing process: the precipitation of a rhombohedral phase and a significant grain growth linked together.