Manganese oxide-zirconium oxide solid solutions. An X-ray diffraction, Raman spectroscopy, thermogravimetry and magnetic study

Manganese oxide-doped ZrO2 samples, prepared by heating mixtures of coprecipitated hydroxides at 1073 K in a H2 stream, were analysed to obtain information on the solid solution (SS) formation. The state and the thermal stability of the incorporated species were also investigated. The samples (Mn up to 14.74 mass%), were studied "as-prepared" and after subsequent thermal treatments in O2 up to 753 K. XRD, Raman spectroscopy, TG and magnetic susceptibility measurements showed that in the "as-prepared" samples (1073 K, H2) a high fraction of Mn is incorporated in the ZrO2 structure, only a small fraction being present as an MnO separate phase. Most of the Mn in SS is present as Mn2+, the remainder as +3 and +4. TG and magnetic measurements revealed that the Mn3+ and/or Mn4+ formed both during the cooling in H2 by reaction with water present as an impurity in the gas phase, and during exposure to the atmosphere. As the Mn in SS increases, the ZrO2 unit cell volume slightly decreases. The SS formation favours the tetragonal and the cubic modifications at the expense of the thermodynamically stable monoclinic phase. When the samples are heated up to 753 K in O2, the Mn2+ in SS is partially oxidised to Mn3+ and/or Mn4+. 33 refs.