María Luisa Sanjuán

Praseodymium oxides present redox properties analogous to those of Ce‐based systems and have been proposed for catalytic applications in combination with CeO 2 , ZrO 2 , or both. However, uncertainties remain concerning the nature and redox behavior of Pr‐rich mixtures, especially with ZrO 2 . Here we study the eutectic composites of the ZrO 2 –PrO x system, focusing on the sensitivity of their microstructure, phase symmetry, and composition to variations of the processing atmosphere from oxidizing to reducing. Mixed oxides have been produced by a laser‐assisted directional solidification technique in O 2 , air, N 2 , or 5%H 2 (Ar) environment, and the resulting materials have been analyzed by scanning electron microscopy/energy‐dispersive X‐ray spectroscopy, X‐ray diffraction, Raman spectroscopy, and magnetic susceptibility. In air, N 2 , or 5%H 2 (Ar) atmosphere, a lamellar, eutectic‐like microstructure forms, the major phase being the one with less Pr content. Both the Pr concentration in each phase as the PrO x molar percentage of the eutectic composites decrease as the atmosphere becomes more reducing. Both eutectic phases are fluorite‐like when processing in air, whereas in N 2 or 5%H 2 (Ar), the phase with high Pr content is of the A‐R 2 O 3 type, and the phase with low Pr content can be described as a fluorite phase containing C‐R 2 O 3 ‐like short‐range‐ordered regions. The results obtained for samples processed in O 2 suggest that for high enough pO 2 no eutectic forms, in analogy with the ZrO 2 –CeO 2 system. The evolution of the phase composition and symmetry is discussed in terms of the limited stability of the phases found in the ZrO 2 –Pr 2 O 3 system, namely, A‐ or C‐R 2 O 3 ‐like, beyond a certain Pr oxidation degree and oxygen content.