Structural and magnetic characterisation of some mixed metal oxides and oxyhalides

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