Structural and magnetic characterisation of some mixed metal oxides and oxyhalides

Stephens, Deborah Ann (2011). Structural and magnetic characterisation of some mixed metal oxides and oxyhalides. University of Birmingham. Ph.D.

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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.