Transition metal oxides and oxide-halides

Field, Marianne Alice Louise (2004) Transition metal oxides and oxide-halides. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

Transition metal oxides and oxide halides of the composition Ln₃Ba₂Mn₂Cu₂O_12.1, Sr₂Cu_1-yCo_yO₂X₂ (X = Cl, Br), Sr₃Fe_2-yCo_yO₅X₂ (y - 0, 1, 2, X = Cl, Br) and NdSrZn_4-x(CO₃)_y have been synthesised and the structures of these materials characterised using Rietveld analysis of powder X-ray and powder neutron diffraction data, thermogravimetric analysis, differential thermal analysis and infra-red spectroscopy.

The structures of Ln₃Ba₂Mn₂Cu₂O_12.1 (Ln = Eu, Sm) have been determined through structure refinement using neutron diffraction data, and the disorder in the anion, and manganese and copper sub-lattices within the layered compounds noted. The displacement of approximately 15 - 20% of manganese ions into the CuO₂ sheets is likely to preclude the observation of superconductivity in these materials. The partial cross-linking of Cu(Mn)O₅ square-pyramids that occurs in the structure, through the addition of excess oxygen, would also be expected to have an inhibiting effect.

Solid solutions of Sr₂Cu_1-yCo_yO₂Cl₂ and Sr₂Cu_1-yCo_yO₂Br₂ (y = 0.2, 0.4, 0.5, 0.6, 0.8) have been synthesised and their structures characterised by powder X-ray diffraction. The cell parameters change as the copper ion is replaced by cobalt, with a steady increase in the a parameter and gradual decrease in the c parameter. This trend reflects the replacement of a Jahn Teller ion (copper (II) by an ion that is not subject to this effect (high spin cobalt (II)).

The crystal and magnetic structures (where appropriate) of the Ruddlesden-Popper related iron oxyhalides, Sr₃Fe_2-yCo_yO₅X₂ (y = 0, 1, 2, X - Cl, Br) have been studied using powder neutron powder diffraction. The materials consist of double layers of Fe/CoO₅ square pyramids separated along the c direction by SrX ‘rocksalt’ layers. Powder neutron diffraction data were collected at room temperature and 2 K for Sr₃Fe₂O₅Br₂, Sr₃FeCoO₅Cl₂ and Sr₃Co₂O₅Cl₂ whilst the thermal dependence of both the nuclear structure and the long range magnetic order of Sr₃Fe₂O₅Cl₂ in the range 17 K < T < 625 K has been studied, allowing the materials T_Neel= 590 K to be determined. All three phases adopt G-type antiferromagnetic spin structures, with the moments confined within the xy plane. The materials possess low temperature moments μ = 4.40(4) μ_B, μ = 4.07(6) μ_B, and μ_B and μ = 2.11(4) μ_B for Sr₃Fe₂O₅Cl₂, Sr₃Fe₂O₅Br₂ and Sr₃FeCoO₅Cl₂ respectively, indicating the presence of high spin iron (III) in all compounds.