Oxide structure prediction and synthesis


Collins, Christopher ORCID: 0000-0002-0101-4426 Oxide structure prediction and synthesis. Doctor of Philosophy thesis, University of Liverpool.

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Abstract

Introduction: The focus of this chapter is to introduce the perovskite structure, beginning from the ideal cubit perovskite with the ABX3 formula unit. The concept of introducing long range ordering into the material are then presented along with the driving forces behind the extension of the structure. Possible magnetic ordering and solid solutions of perovskites are then presented. This is followed by the introduction of how theoretical chemistry can provide useful information to investigations and begin to predict how new materials can be made and is followed by a summary of the techniques commonly used. Methods: This chapter introduces the experimental methods used within this thesis, along with a description of the diffraction techniques used in the characterisation of oxide materials; including x-ray and neutron diffraction, iodometric titrations and the basic concepts behind Mössbauer spectroscopy. The second part to the chapter provides details on density functional theory (DFT) and force field (FF) calculations that are used throughout the thesis for the prediction of new materials. Chapter 3: Details the use of a series of calculations with DFT on the chemical substitution in the YBa2Fe3-xMxO8 (where M = Co, Ni and Mn), where the calculations are first tested on doping with Co, where it has been previously been experimentally reported. Calculations for un-reported substitutions a new compound is predicted. Synthetic investigations are then undertaken across the series, and a new material found where DFT calculations predict a new compound. Characterisation of the new material reveals that it has a crystal structure in good agreement with the structure predicted by DFT. Chapter 4: Computationally investigates doping in the YBa2Ca2Fe5-xMxO13 (M = Co, Cu, Mn, Ni, Ti and Zn) solid oxide fuel cell cathode material using DFT. The results from the calculations predict stable doping for Cu and Co, with small doping levels favoured for M = Ni and Zn, with M = Mn yielding results predicting marginal doping and doping not favoured at all for M = Ti. Chapter 5: When D. Hodgeman was experimentally investigating Cu doping of the YBa2Ca2Fe5O13 material an unknown perovskite superstructure was observed by x-ray diffraction. This chapter then focuses on the development of the Extended Module Materials Assembly (EMMA) method. The method is validated be correctly computing the correct crystal structure for the YBa2Ca2Fe5O13 perovskite and is used to predict the structure for the new Y2.24Ba2.28Ca3.48Fe7.44Cu0.56O21perovskite. The crystal structure predicted by EMMA is then used as the basis for the experimental refinement of the structure and the structures found to be in good agreement.

Item Type: Thesis (Doctor of Philosophy)
Additional Information: Date: 2013-11 (completed)
Subjects: ?? QD ??
Depositing User: Symplectic Admin
Date Deposited: 13 Feb 2014 10:57
Last Modified: 16 Dec 2022 04:40
DOI: 10.17638/00014055
Supervisors:
URI: https://livrepository.liverpool.ac.uk/id/eprint/14055
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