Eutectic ceramics of the CeO2–ZrO2–MgO system produced by laser-assisted directional solidification

• Published in: Journal of solid state chemistry 2022-11, Vol.315, p.123525, Article 123525
• Main Authors: Orera, Alodia, Oliete, Patricia B., Merino, Rosa I., Sanjuán, María Luisa
• Format: Article
• Language: English
• Subjects: CeO2–ZrO2–MgO; CO2 separation membranes; Directional solidification; Eutectic ceramics
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/j.jssc.2022.123525

Oxide eutectics have great potentiality as structural or functional materials, owing to the outstanding properties derived from the eutectic microstructure. Among them, the eutectic of the ZrO2–MgO system is particularly noteworthy because of the unusual combination of thermomechanical, optical and electrical properties. In a recent application, Zr1-δMgδO2-δ – MgO eutectic oxides have been used to produce porous supports for molten-carbonate based CO2 separation membranes. Here we explore composite ceramic oxides of the CexZr1-xO2 – MgO (x ≤ 0.5) system with eutectic microstructure, with the motivation that incorporating cerium may enhance the CO2 permeation properties. Eutectic composites with different cerium content are produced by a laser-assisted directional solidification technique at variable solidification rate, v. In all cases the composite bicrystal consists of two phases, MgO and a fluorite-like (CexZr1-x)1-yMgyO2-y phase. A purely fibrilar microstructure is found for x ≥ 0.3 at v = 25 mm/h, with MgO fibres embedded within the fluorite-like matrix. The MgO mol% in the eutectic composites decreases from ∼53% for x = 0 to ∼48% for x = 0.5. X-ray and Raman results evidence long-range ordering in a quasi-tetragonal monoclinic symmetry for x = 0.5. Impedance spectroscopy results are consistent with a change from ionic to mainly electronic conductivity when the atmosphere is changed from air or Ar to 5%H2–Ar. [Display omitted] •Eutectic ceramics of the ZrO2–CeO2–MgO system are produced by directional solidification.•MgO fibres appear embedded in a fluorite-like (CexZr1-x)1-yMgyO2-y matrix.•Long-range monoclinic symmetry in the matrix for x (Ce) = 0.5•Oxide-ion conductivity in air, n-type in reducing atmosphere.•Suitable candidates as MIEC supports for dual CO2-selective membranes.