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Title: Multi-scale simulation of electroceramics
Author: Ward, Robyn Elizabeth
ISNI:       0000 0004 7428 2784
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2018
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This thesis used a range of simulation techniques to investigate the various effects rareearth element doping has on barium titanate with a focus on their ability to increase the lifetime of such ceramics. Finite element simulation was used to look for a relationship between user generated regional input permittivities, conductivities and microstructures based on experimental core-shell microstructures formed in rare-earth element doped barium titanate and the simulated bulk output properties. No simple analytical relationship was found. Input properties for more local regions are needed for accurate simulations. These cannot easily be obtained from experiment. Experimental spectra (XRD and TEM) of perovskites were simulated from molecular dynamics simulations. The simulated spectra include dynamical information. The spectra along with the in-house analytical PALAMEDES code were used to interpret tilt features in the simulated systems. The code gives quantitative values for tilt and volumes for A and B sites in the system and identifies tilt phase. Static simulations of doped barium titanate demonstrate the affinity of rare-earth dopants to form specific compensation schemes. The simulation results agree with experiment. Lifetime improvements due to rare-earth dopants have been theorised to be due to oxygen vacancy trapping. Further simulations show that all mid-size trivalent rare-earth elements can strongly trap oxygen vacancies. The differences seen in lifetime improvements between rare-earths is due to their distribution and compensation schemes they adopt. Advanced sampling techniques were used to look at self-diffusion and rare-earth diffusion in barium titanate. The applicability of Mean Squared Displacement, Steered MD, Umbrella sampling and Metadynamics to solid-state systems is discussed. The selfdiffusion results agreed with available experimental values. Dysprosium was found to be the most mobile rare-earth of those investigated in barium titanate lattice suggesting that a combination of its mobility and preference to dope in a self-compensatory manner is the reason for its superior lifetime improvements.
Supervisor: Harding, J. H. ; Freeman, C. L. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available