Preparation and characterisation of high oxidation state compounds of transition models
Preparation and characterisation of high oxidation state compounds of transition models
The synthesis of a range of complex oxides containing iron(IV), cobalt(IV) and nickel(III) is reported. These materials have been characterised by powder x-ray and neutron diffraction, thermogravimetric analysis, Mösbauer spectroscopy and magnetic and electrical measurements.
A new, pure iron(IV) phase, Sr2FeO4 has been synthesised and studied. This material crystallises with the K2NiF4 structure with an unusually regular octahedral coordination around the high spin d4 iron. No evidence for structural distortion has been found on cooling to 4.2K. The Nél temperature has been determined at 64K. Mösbauer measurements have shown the magnetic structure to be based on a spin helix; although the 4.2K neutron diffraction pattern only showed evidence of ordering in two-dimensions.
The system Sr3Fe27-y (0≤y≤1), which adopts the Ruddlesden-Popper phase intergrowth of SrFeO3 (perovskite) and Sr2FeO4 (K2NiF4), has been studied. The Nél temperature has been determined at 110K and the electronic dn configuration high spin d4. A charge disproportionation reaction is evidenced by Mösbauer spectroscopy in the pure Fe(IV) material such that Fe4+⇌ Fe^3+ + Fe^5+ . Magnetic ordering has been shown to occur in two-dimensions only with a doubled a lattice parameter. For oxygen stoichiometries below seven, one oxygen site in the perovskite block becomes partially occupied and is completely empty at y = 1, producing an unusual square pyramidal iron(III) coordination.
A new strontium cobaltate, Sr_3Co_2O_7-z has been prepared. This material possesses a structure similar to the Ruddlesden-Popper phase Sr_3Ti_2O_7, but triples in the b lattice direction as z increases above 1.0. Tripling is a result of oxygen ordering where one oxygen site is completely and two others partially occupied.
Mixed transition-metal oxide phases have been studied in the system Sr_3M_2-xN_xO_7-g M,N = Fe, Co and Ni. The cobalt/nickel system adopts the tripled orthorhombic phase at low nickel content, resuming the tetragonal Sr_3Ti_2O_7 structure at higher nickel levels. Refinement of neutron diffraction data indicates partial oxygen occupancy on two oxygen sites.
University of Southampton
Dann, Sandra E
bfa9eae2-bb8d-4499-801b-86b0c0c49946
1994
Dann, Sandra E
bfa9eae2-bb8d-4499-801b-86b0c0c49946
Dann, Sandra E
(1994)
Preparation and characterisation of high oxidation state compounds of transition models.
University of Southampton, Doctoral Thesis, 243pp.
Record type:
Thesis
(Doctoral)
Abstract
The synthesis of a range of complex oxides containing iron(IV), cobalt(IV) and nickel(III) is reported. These materials have been characterised by powder x-ray and neutron diffraction, thermogravimetric analysis, Mösbauer spectroscopy and magnetic and electrical measurements.
A new, pure iron(IV) phase, Sr2FeO4 has been synthesised and studied. This material crystallises with the K2NiF4 structure with an unusually regular octahedral coordination around the high spin d4 iron. No evidence for structural distortion has been found on cooling to 4.2K. The Nél temperature has been determined at 64K. Mösbauer measurements have shown the magnetic structure to be based on a spin helix; although the 4.2K neutron diffraction pattern only showed evidence of ordering in two-dimensions.
The system Sr3Fe27-y (0≤y≤1), which adopts the Ruddlesden-Popper phase intergrowth of SrFeO3 (perovskite) and Sr2FeO4 (K2NiF4), has been studied. The Nél temperature has been determined at 110K and the electronic dn configuration high spin d4. A charge disproportionation reaction is evidenced by Mösbauer spectroscopy in the pure Fe(IV) material such that Fe4+⇌ Fe^3+ + Fe^5+ . Magnetic ordering has been shown to occur in two-dimensions only with a doubled a lattice parameter. For oxygen stoichiometries below seven, one oxygen site in the perovskite block becomes partially occupied and is completely empty at y = 1, producing an unusual square pyramidal iron(III) coordination.
A new strontium cobaltate, Sr_3Co_2O_7-z has been prepared. This material possesses a structure similar to the Ruddlesden-Popper phase Sr_3Ti_2O_7, but triples in the b lattice direction as z increases above 1.0. Tripling is a result of oxygen ordering where one oxygen site is completely and two others partially occupied.
Mixed transition-metal oxide phases have been studied in the system Sr_3M_2-xN_xO_7-g M,N = Fe, Co and Ni. The cobalt/nickel system adopts the tripled orthorhombic phase at low nickel content, resuming the tetragonal Sr_3Ti_2O_7 structure at higher nickel levels. Refinement of neutron diffraction data indicates partial oxygen occupancy on two oxygen sites.
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94107476
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Published date: 1994
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Local EPrints ID: 462805
URI: http://eprints.soton.ac.uk/id/eprint/462805
PURE UUID: 40ee530c-3ef0-40fe-8213-b8f41e7c2a9d
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Date deposited: 04 Jul 2022 20:05
Last modified: 16 Mar 2024 18:58
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Author:
Sandra E Dann
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