Year: 2011
Type: dissertation
Abstract: This thesis investigates the structural and physical effects of changing the ratio of Mn:Ga in the anion deficient perovskite, YSr\\(_3\\)Mn\\(_{4-x}\\)GaxO\\(_{10.5}\\). YSr\\(_3\\)Mn\\(_{4-x}\\)GaxO\\(_{10.5}\\) crystallises in the tetragonal space group I4/mmm, with lattice parameters a~7.64 Å and c~15.66 Å. Magnetic characterisation indicates that the material is antiferromagnetic overall, with ferromagnetic ordering in the [001] direction of the unit cell. Earlier work on the structural analogue, Y\\(_{1.07}\\)Sr\\(_{2.93}\\)Mn\\(_{2.67}\\)Ga\\(_{1.33}\\)O\\(_{10.5}\\), identified a magnetic peak in the neutron diffraction pattern that could not be fitted following refinement of NPD data. This work concluded that the extra peak was due to a small MnO impurity. The effects of oxidation and fluorination on the structural and physical properties of YSr\\(_3\\)Mn\\(_{4-x}\\)Ga\\(_x\\)O\\(_{10.5}\\) with various Mn:Ga ratios are investigated. The physical and structural effects of substituting Mn\\(^{3+}\\) or Co\\(^{3+}\\) for Fe\\(^{3+}\\) in the perovskite related material, Pb\\(_4\\)Fe\\(_3\\)O\\(_8\\)Cl, have been investigated using XRPD, NPD and magnetic susceptibility measurements. An earlier characterisation of Pb\\(_8\\)WO\\(_{10}\\)Cl\\(_2\\) suggested a deficit on all atom sites within the unit cell. This work suggests a different structure with an intact cation and main oxygen sub-lattice. The site of an additional oxygen was established linked to tungsten. Pb\\(_8\\)WO\\(_{10}\\)Cl\\(_2\\) crystallises in space group I4/mmm, with a = 3.9846(2) and c = 22.690(2) Å.
Author: Deborah Ann Stephens
Language: English
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W203886658