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Title: Synthesis, structure and magnetic properties of some low dimensional metal compounds
Author: Patel, Rina
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2008
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A selection of low dimensional metal compounds have been synthesised; the structures and magnetic properties of these materials have been characterised using Rietveld analysis of powder X-ray and powder neutron data and magnetic susceptibility measurements. Refinements on the LnSrSc04 (Ln = La ~ Sm) were performed in several space groups accommodating octahedral tilts. Based on the statistics the Abma description was used to model the data and the orthorhombic distortion results from tilting of the SC06 octahedra within the perovskite: layer. Graphs of the alb ratio against temperature show that the level of distortion increases between 25 - 300°C and decreases between 300 - 1200 °C; for LaSrSc04 and PrSrSc04 the compounds revert to the ideal KzNiF4-type structure at approximately 900 and 1100 °C respectively. A similar analysis was undertaken for LnSrln04 (Ln = La and Prj, these compounds adopt the Pbca space group at room temperature. A comprehensive study has been carried out to investigate the factors that lead to the choice of structure and drive distortions of the K2NiF4-type structure away from an 14/mmm description. An investigation into the LnSrCo04(Ln = La - Gd) series has been performed. As the smaller lanthanides are incorporated into the structure (La-Er), the K2NiF4 structure is maintained until Tb. At which point the mismatch between the perovskite Co-O layer and the rocksalt Ln)-O layers become too great, resulting in the formation of SrLnZ04. Graphs of Co-O axial bond distances against temperature were plotted in order to determine whether a thermally induced spin transition occurs, anomalous behaviour for all compounds was observed. A comparison of the thermal expansion of the axial B-O distances in the compounds; LaSrCo04, LaSrFe04, La\8SrozCu04 and LaBaCo04 enabled us to identify that the Co3+ compounds expand much faster in the apical direction. If low spin Co3 +, (tzg 6, ego) dxldzldxi can be thermally excited to an intermediate-spin, (tzg5egl), the electron density would transfer to the dzz orbital. This would expand the axial distance faster than a normal thermal effect. Based on this there is strong evidence that a spin transition occurs in these compounds. Novel analogues ofLa2B%Co4015 have been synthesised by replacing La3+ with Nd3+ and Sm3 +. The structure of these phases and the previously reported LazBa6Co401S have been determined from analysis of neutron diffraction data and adopt the P63mc space group. The compound consists of one Co06 octahedron and three Co04 tetrahedra linked by corner sharing oxygen ions, forming a C040 1S cluster. The clusters form a triangular based lattice that resembles a honeycomb. Magnetic data reveal an antiferromagnetic transition due to the long range ordering of clusters at 4, 8.5 and 17.5 K for Ln2B%Co4015 (Ln = La, Nd and Sm) respectively. The ZFC and FC susceptibilities have been discussed in detail. Three complex transition metal triazole compounds have been synthesised and investigated by single crystal X-ray diffraction. 1) [Co2CI(3-amino-l,2,4-triazole)31 is an intriguing magnetically coupled coordination network. The implications of the observed ferrimagnetic ordering are discussed in the context of the topological structural disorder. The compound was obtained from a hydrothermal synthesis, crystallising in a primitive hexagonal cell a good structural model fur [Co2CI(3-amino-l,2,4-triazole)3] was obtained in the non-polar space group P6/mmc, revealing a 3-D coordination network. 2) [CuCI(3-amino-l,2,4-triazole)z.Cl] crystallises in the orthorhombic space group Pbcm and displays a zig-zag polymeric structure_ 3) [CusCh(3,5diamino- triazolate)3lHzO consists of unusual chains of trinuclear units with a 3,5-diaminotriazole linking the trimeric units. These trimeric entities are bridged by Cu coordinated to CI forming a chain, which are in turn linked by Cu-CI in a zig-zag formation to form layers,
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available