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Investigation of tunable buffer layers for coated superconductors: from solid state physics to quantum chemistry

Danny Vanpoucke UGent (2012)
abstract
High temperature ceramic superconductors can be grown in layered structures on metallic wires to provide the mechanical flexibility required for industrial applications. To prevent the metal atoms from diffusing into the superconductor –destroying its superconductivity– buffer layers are grown between the metal substrate and the superconductor. Recently, cerium oxide has been used as such a buffer layer. However, the layer thickness of these buffer layers is limited by the formation of cracks during deposition. This behaviour has been linked to internal stress due to lattice mismatch and different thermal expansion coefficients of the substrate and the buffer layer. A simple way to reduce these mismatches is through metal doping. In this work, we study the influence of dopants on the properties of cerium oxide through the use of ab initio calculations. Trends in the stability, lattice parameter, bulk modulus and thermal expansion coefficient of cerium oxide doped with different dopants are investigated. In addition, the influence of charge compensating oxygen vacancies is studied, and their role in the stability of heavily La-doped cerium oxide (La2Ce2O7) is presented. The use of dopants with different valences also leads to a modification of the charge distribution around the dopant sites. A way to have a more quantitative estimate of the charge transfer induced by dopants is via the introduction of the chemical concept of ‘atoms in a molecule’ into solids. This can be considered a first step in the direction of answering the experimental question: What is the charge of a given atom in a certain compound? In this work we present an implementation of this Hirshfeld method for solids, and calculate the atomic charges in doped cerium oxides.
Please use this url to cite or link to this publication:
author
promoter
UGent and UGent
organization
year
type
dissertation (monograph)
subject
keyword
ceria, doping, cerium oxides, ab initio calculations, atoms in molecules, DFT, Hirshfeld-I, lanthanum cerate
pages
XIV, 204 pages
publisher
Ghent University. Faculty of Sciences
place of publication
Ghent, Belgium
defense location
Gent : Faculteit Ingenieurswetenschappen en Architectuur (Jozef Plateauzaal)
defense date
2012-10-05 15:00
language
English
UGent publication?
yes
classification
D1
additional info
dissertation consists of copyrighted material
copyright statement
I have transferred the copyright for this publication to the publisher
id
3010215
handle
http://hdl.handle.net/1854/LU-3010215
date created
2012-10-09 16:54:27
date last changed
2012-10-10 09:25:48
@phdthesis{3010215,
  abstract     = {High temperature ceramic superconductors can be grown in layered structures on metallic wires to provide the mechanical flexibility required for industrial applications. To prevent the metal atoms from diffusing into the superconductor --destroying its superconductivity-- buffer layers are grown between the metal substrate and the superconductor. Recently, cerium oxide has been used as such a buffer layer. However, the layer thickness of these buffer layers is limited by the formation of cracks during deposition. This behaviour has been linked to internal stress due to lattice mismatch and different thermal expansion coefficients of the substrate and the buffer layer. A simple way to reduce these mismatches is through metal doping.
In this work, we study the influence of dopants on the properties of cerium oxide through the use of ab initio calculations. Trends in the stability, lattice parameter, bulk modulus and thermal expansion coefficient of cerium oxide doped with different dopants are investigated. In addition, the influence of charge compensating oxygen vacancies is studied, and their role in the stability of heavily La-doped cerium oxide (La2Ce2O7) is presented.
The use of dopants with different valences also leads to a modification of the charge distribution around the dopant sites. A way to have a more quantitative estimate of the charge transfer induced by dopants is via the introduction of the chemical concept of {\textquoteleft}atoms in a molecule{\textquoteright} into solids. This can be considered a first step in the direction of answering the experimental question: What is the charge of a given atom in a certain compound? In this work we present an implementation of this Hirshfeld method for solids, and calculate the atomic charges in doped cerium oxides.},
  author       = {Vanpoucke, Danny},
  keyword      = {ceria,doping,cerium oxides,ab initio calculations,atoms in molecules,DFT,Hirshfeld-I,lanthanum cerate},
  language     = {eng},
  pages        = {XIV, 204},
  publisher    = {Ghent University. Faculty of Sciences},
  school       = {Ghent University},
  title        = {Investigation of tunable buffer layers for coated superconductors: from solid state physics to quantum chemistry},
  year         = {2012},
}

Chicago
Vanpoucke, Danny. 2012. “Investigation of Tunable Buffer Layers for Coated Superconductors: From Solid State Physics to Quantum Chemistry”. Ghent, Belgium: Ghent University. Faculty of Sciences.
APA
Vanpoucke, D. (2012). Investigation of tunable buffer layers for coated superconductors: from solid state physics to quantum chemistry. Ghent University. Faculty of Sciences, Ghent, Belgium.
Vancouver
1.
Vanpoucke D. Investigation of tunable buffer layers for coated superconductors: from solid state physics to quantum chemistry. [Ghent, Belgium]: Ghent University. Faculty of Sciences; 2012.
MLA
Vanpoucke, Danny. “Investigation of Tunable Buffer Layers for Coated Superconductors: From Solid State Physics to Quantum Chemistry.” 2012 : n. pag. Print.