<p>A series of layered perovskite-based compounds were synthesized and studied as follows.</p> <p>La<sub>5</sub>Mo<sub>2.76(4)</sub>V<sub>1.25(4)</sub>O<sub>16</sub> is a new pillared-perovskite synthesized by solid state chemistry method. It has layers of corner-sharing octahedra separated by dimers of edge-sharing octahedra, and is the first Mo-based pillared-perovskite whose magnetic structure was determined by neutron diffraction.</p> <p>Ca<sub>2</sub>FeMnO<sub>5</sub> is an oxygen-deficient-perovskite with a brownmillerite-type ordering of oxygen vacancies, resulting in layers of corner-sharing octahedra separated by chains of corner-sharing tetrahedra. The octahedral layer contains mostly (~87%) Mn, while the tetrahedral layer is mainly (~91%) occupied by Fe. Long-range G-type magnetic ordering is present, where the moment on each site is coupled antiferromagnetically relative to all nearest neighbors.</p> <p>Ca<sub>2</sub>FeCoO<sub>5</sub> has a brownmillerite superstructure with space group <em>Pcmb</em>, a rare space group for brownmillerites that requires doubling of one unit cell axis. Ca<sub>2</sub>FeCoO<sub>5 </sub>is the first brownmillerite to contain intra-layer cation ordering. It has a long-range G-type ordering, and is the first brownmillerite to show spin re-orientation as function of temperature.</p> <p>Sr<sub>2</sub>FeMnO<sub>5+y</sub> was synthesized in both air (y~0.5) and argon (y~0), both of which resulted in vacancy-disordered cubic structures. The argon compound has a local brownmillerite structure, i.e. local ordering of vacancies. It has a superparamagnetic state below ~55K, with domains of short range (50Å) G-type ordering at 4K. For the air synthesized compound, y~0.5, long range G-type ordering is observed in ~4% of the sample.</p> <p>Sr<sub>2</sub>Fe<sub>1.9</sub>M<sub>0.1</sub>O<sub>5+y</sub> (M=Mn, Cr, Co; y= 0, 0.5) were synthesized in both air(y~0.5), and argon(y~0). All argon materials are brownmillerites with G-type magnetic ordering, but T<sub>N</sub>’s are significantly different. The air-synthesized Co-material has long range vacancy ordering and magnetic ordering, while the Mn and Cr-materials (air) lack such orderings and both show spin-glass-like transitions.</p> <p>Sr<sub>2</sub>Fe<sub>1.5</sub>Cr<sub>0.5</sub>O<sub>5</sub> has a vacancy-disordered cubic structure, but contains long range G-type magnetic ordering, unlike the other vacancy-disordered materials studied.</p> / Doctor of Philosophy (PhD)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/11074 |
| Date | 10 1900 |
| Creators | Ramezanipour, Farshid |
| Contributors | Greedan, John E., Jacques Barbier, Yurij Mozharivskyj, Jacques Barbier, Yurij Mozharivskyj, Chemistry |
| Source Sets | McMaster University |
| Detected Language | English |
| Type | thesis |
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