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Thermodynamics of structural vacancies in titanium monoxide from first principles calculations
KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.ORCID-id: 0000-0002-9920-5393
KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
2005 (engelsk)Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 71, nr 14, s. 144101-Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

The structure, stability and electronic properties of the low oxygen oxides of titanium, TiOx with 1/3 <= x <= 3/2, have been studied by means of accurate first-principles calculations. In both stoichiometric and nonstoichiometric TiO there are large fractions of vacant lattice sites. These so-called structural vacancies are essential for understanding the properties and phase stability of titanium oxides. Structures with an ordered arrangement of vacancies were treated with a plane wave pseudo-potential method, while calculations for structures with disordered vacancies were performed within the framework of the Korringa-Kohn-Rostoker Green's function technique. The relaxed structural parameters in general compare well with experimental data, though some discrepancies exist for stoichiometric TiO in the ideal B1 structure, i.e., without any vacancies. The equation of state as well as the elastic properties are also derived. A monoclinic, vacancy-containing, structure of stoichiometric TiO is confirmed to be stable at low temperature and pressure. Experimentally a transition from a stoichiometric cubic structure with disordered vacancies to the ideal B1 structure without any vacancies has been observed at high pressure. It is discussed how this experimental observation relates to the present theoretical results for defect-containing and defect-free TiO.

sted, utgiver, år, opplag, sider
2005. Vol. 71, nr 14, s. 144101-
Emneord [en]
Total-Energy Calculations, Augmented-Wave Method, Electronic-Structure, Lattice-Dynamics, Basis-Set, Tio, Metals, Oxides, Films, Vanadium
HSV kategori
Identifikatorer
URN: urn:nbn:se:kth:diva-6885DOI: 10.1103/PhysRevB.71.144101ISI: 000228758700017Scopus ID: 2-s2.0-28744436258OAI: oai:DiVA.org:kth-6885DiVA, id: diva2:11725
Merknad

QC 20100622

Tilgjengelig fra: 2007-03-14 Laget: 2007-03-14 Sist oppdatert: 2017-12-14bibliografisk kontrollert
Inngår i avhandling
1. From the Electronic Structure of Point Defects to Functional Properties of Metals and Ceramics
Åpne denne publikasjonen i ny fane eller vindu >>From the Electronic Structure of Point Defects to Functional Properties of Metals and Ceramics
2007 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

Point defects are an inherent part of crystalline materials and they influence important physical and chemical properties, such as diffusion, hardness, catalytic activity and phase stability. Increased understanding of point defects enables us to tailor the defect-related properties to the application at hand. Modeling and simulation have a prominent role in acquiring this knowledge. In this thesis thermodynamic and kinetic properties of point defects in metals and ceramics are studied using first-principles calculations based on density functional theory. Phenomenological models are used to translate the atomic level properties, obtained from the first-principles calculations, into functional materials properties. The next paragraph presents the particular problems under study.

The formation and migration of vacancies and simple vacancy clusters in copper are investigated by calculating the energies associated with these processes. The structure, stability and electronic properties of the low-oxygen oxides of titanium, TiOx with 1/3 < x < 3/2, are studied and the importance of structural vacancies is demonstrated. We develop an integrated first-principles and Calphad approach to calculate phase diagrams in the titanium-carbon-nitrogen system, with particular focus on vacancy-induced ordering of the substoichiometric

carbonitride phase, TiCxNy (x+y < 1). The possibility of forming higher oxides of plutonium than plutonium dioxide is explored by calculating the enthalpies for nonstoichiometric defect-containing compounds and the analysis shows that such oxidation is only produced by strong oxidants. For ceria (CeO2) doped with trivalent ions from the lanthanide series we probe the connection between the choice of a dopant and the improvement of ionic conductivity by studying the oxygen-vacancy formation and migration properties. The significance of minimizing the dopant-vacancy interactions is highlighted. We investigate the redox thermodynamics of CeO2-MO2 solid solutions with M being Ti, Zr, Hf, Th, Si, Ge, Sn or Pb and show that reduction is facilitated by small solutes.

The results in this thesis are relevant for the performance of solid electrolytes, which are an integral part of solid oxide fuel cells, oxygen storage materials in automotive three-way catalysts, nuclear waste materials and cutting tool materials.

sted, utgiver, år, opplag, sider
Stockholm: Materialvetenskap, 2007
Emneord
first principles, ab initio, density functional theory, Calphad, point defects, diffusion, solid electrolytes, oxygen storage materials
HSV kategori
Identifikatorer
urn:nbn:se:kth:diva-4309 (URN)978-91-7178-590-9 (ISBN)
Disputas
2007-03-30, F2, Lindstedtsvägen 26, Stockholm, 10:00
Opponent
Veileder
Merknad
QC 20100622Tilgjengelig fra: 2007-03-14 Laget: 2007-03-14 Sist oppdatert: 2012-03-22bibliografisk kontrollert

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