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| Identifier |
000379382 |
| Title |
Μικροπορώδη οξείδια μετάλλων μετάβασης μικτού σθένους : σύνθεση - δομή - μαγνητοηλεκτρονικές ιδιότητες |
| Alternative Title |
Mixed valence microporous transition metal oxides : synthesis - structure - magnetoelectronic properties |
|
Author
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Αδαμόπουλος, Οθωνας Παν.
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Thesis advisor
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Λάππας, Αλέξανδρος
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Reviewer
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Τρικαλίτης, Παντελής
Φρουδάκης, Γεώργιος
|
| Abstract |
The thesis focuses on frustrated systems of mixed-valence transitional metal oxides. That is to say, on
systems, the symmetry of which leads to the development of competing interactions that can hardly
minimize their energy simultaneously. The main mixed-valence transition metal is Mn. We exploit the
capability of multi-valence state and synthesise compounds with multi coordination numbers. In its oxides
the structure is composed of Mn3+O6 octahedral units with common edges or vertices, forming prototype
porous complexes. Their microporous and layered structure further intensifies the geometric frustration,
while their spin-lattice interactions become more intriguing, when alkali metal cations get intercalated in
it. The derived compounds belong to the generic group of delafossites, A+M3+O2.
The parent delafossite is α-NaMnO2, the lattice of which consists of MnO2 layers with intercalated
Na+ cations. It is further studied, regarding the crystal structure stability and the magnetic properties of its
non-stoichiometric compounds, the phase transition, its structural changes employing synchrotron
radiation and microscopic magnetic excitations by inelastic neutrons scattering. The sub-stoichiometric
compounds are two-phase, while α-NaMnO2 exhibits a spin-gap at Τ≤ΤΝ=45 Κ, the magnetic interactions
are mainly developed along b-axis and the spin-fluctuations are one-dimensional, along the same axis.
Additionally, the isostructural CuMnO2 is studied, in the structure of which the intercalant cations have
been replaced by Cu+. It has been synthesized under a new synthesis protocol and characterised, with
respect to its thermal stability and magnetic properties. Moreover, its crystal and magnetic structure have
been analysed by synchrotron and neutron powder diffraction, respectively. It demonstrates a phase
transition from monoclinic to triclinic at TΝ=68 Κ with large structural changes, while it also has a spin-gap
at Τ≤ΤΝ. Eventually, the two delafossites are compared. Furthermore, there have been attempts to
synthesise and study the complementary compounds: the β-NaMnO2 polymorph, the NaVO2 homologues
system and the K0.125MnO2 analogue. The goal is the comparison of their structures and the
comprehension of the correlation between the magnetostructural mechanisms and their physicochemical
properties.
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| Language |
Greek |
| Subject |
crystal / magnetic structure |
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frustration |
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magnetoelectronic properties |
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microporous / layered structure |
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transition metals |
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Χ-ray diffraction / neutron scattering |
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κρυσταλλική / μαγνητική δομή |
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μέταλλα μετάβασης |
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μαγνητοηλεκτρονικές ιδιότητες |
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μικροπορώδης / φυλλόμορφη δομή |
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περίθλαση ακτίνων-Χ / σκέδαση νετρονίων |
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‘όχληση’ |
| Issue date |
2012-05-11 |
| Collection
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School/Department--School of Sciences and Engineering--Department of Chemistry--Doctoral theses
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|
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Type of Work--Doctoral theses
|
| Views |
767 |
Μικροπορώδη οξείδια μετάλλων μετάβασης μικτού σθένους : σύνθεση - δομή - μαγνητοηλεκτρονικές ιδιότητες
