Synthesis and characterization of ternary manganese oxides

Kristina Uusi-Esko

    Research output: ThesisDoctoral ThesisCollection of Articles

    Abstract

    The demand for novel functional materials is a never-ending challenge, as the development of many future applications depends on the new innovations made in the field of materials science. Ternary manganese oxides are a versatile group of materials with interesting magnetic properties and several potential applications, e.g. in microelectronics and solid oxide fuel cells. This thesis reports the preparation of several ternary manganese oxide materials through a selection of synthesis methods. Studies on the structural details, magnetic properties and oxygen stoichiometry of the bulk and thin-film samples are moreover included in this work. The thesis consists of four publications, discussed with relevant literature data. The synthesis of an entire series of the hexagonal RMnO3 system for R = Y, Ho-Lu, and the subsequent conversion of the hexagonal phases to orthorhombic perovskites through high-pressure treatment is realized in the present work. The synthesis methods of the hexagonal bulk samples reported here include the hydrothermal and the sol-gel methods. A systematic study of the structural evolution is presented for both polymorphs, and studies on the magnetic properties have been performed as well. High-quality thin-film samples of the hexagonal and orthorhombic RMnO3 families have been fabricated employing the atomic layer deposition (ALD) technique and post-deposition heat treatment. The formation of metastable orthorhombic RMnO3 perovskites of the small rare earths has been successfully realized even for the smallest R constituent, Lu, by depositions on coherent perovskite substrates with low lattice mismatch with the targeted structure. The challenging task of studying the magnetic properties of these thin-film samples is also approached in the present work. The Néel temperatures determined for the RMnO3 films featuring antiferromagnetic ordering are in good accordance with the corresponding results on powder samples, and the presence of cation vacancies is shown for the ALD-grown LaMnO3+δ sample. The reproducible fabrication of spinel-structured (Mn,Co)3O4 thin films by ALD has been achieved and reported. Precise control of the oxygen content of as-deposited MnCo2O4+δ films has been realized for the first time for an ALD-grown thin-film sample through post-deposition heat treatments, as evidenced from the monotonous increases of both the unit-cell volume and the Curie temperature with increasing annealing temperature/decreasing oxygen partial pressure. The performance of ALD-grown MnCo2O4 protective coatings is also reported on ferritic stainless steel in solid oxide fuel cells with promising results.
    Translated title of the contributionSynthesis and characterization of ternary manganese oxides
    Original languageEnglish
    QualificationDoctor's degree
    Awarding Institution
    • Aalto University
    Supervisors/Advisors
    • Karppinen, Maarit, Supervisor
    Publisher
    Print ISBNs978-952-60-4177-3
    Electronic ISBNs978-952-60-4178-0
    Publication statusPublished - 2011
    MoE publication typeG5 Doctoral dissertation (article)

    Keywords

    • manganese oxide
    • high-pressure synthesis
    • atomic layer deposition
    • thin film
    • magnetic properties
    • oxygen stoichiometry

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