Investigating the electronic structure of fluorite-structured oxide compounds: comparison of experimental EELS with first principles calculations

Aguiar, J. Albino; Ramasse, Quentin M.; Asta, Mark; Browning, Nigel D.

doi:10.1088/0953-8984/24/29/295503

Cited by 9 publications

(12 citation statements)

References 48 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Our current DFT model fails to correctly cancel out the self-interaction energy leading to delocalization of the Ce 4f electrons which shifts the 4f levels down in energy. The simulate edge shape matches most of the predictions from other DFT methods seen in literature which show similar relative peak height trends [4]. Grain boundary structures were modelled using the method proposed by Braithwaite et al [5].…”

supporting

confidence: 70%

Predicting the Electronic Structure of CeO₂ Grain Boundaries for Comparison with Atomic Resolution EELS

2017

View full text Add to dashboard Cite

Intermediate temperature solid oxide fuel cells are an attractive energy source for converting hydrocarbon fuels into electrical energy. However, the highly resistive grain boundaries (GB) in these polycrystalline electrolytic materials leads to a significant decrease in the overall ionic conductivity. One of the most popular theories for the origin of this increased resistivity across electrolytic GB's is an intrinsic resistance arising from a so-called space charge potential region surrounding the GB core. Recent electron energyloss spectroscopy (EELS) analysis on doped CeO2 shows that grain boundary dopant segregation may also be a significant factor influencing oxygen migration energy [1,2]. To gain a fundamental understanding of the underlying GB charge transport mechanisms in ceria-based oxides, we are modelling the relationship between GB character, composition, electronic structure and conductivity. Initially, density functional theory was employed to determine the bonding for a select number of stoichiometric CeO2 symmetric tilt boundaries. Preliminary calculations are compared with experimentally determined EELS from CeO2.All computations were performed using the local density approximation (LDA) exchange-correlation functional with spin-polarization considered. Within LDA formalism, the Kohn-Sham equations were solved through the implementation of projector augmented wave (PAW) method using a plane-wave basis set as implemented in VASP [3]. The energies were converged within 1 meV with k-point sampling during all optimization carried out on a Monkhorst-Pack grid of 8x8x8 for bulk calculations and 1x5x5 for the GB supercells with a plane-wave cut-off of 400 eV. For a more accurate representation of the Fermi level and partial occupancies, the tetrahedron method with Blӧchl corrections and the Davidson-block iteration scheme was used.To validate the choice of pseudopotential, a comparison of simulated and experimental EELS oxygen Kedge was carried out for bulk CeO2. Figure 1 shows a good qualitative match between experiment and theory. The first peak in the simulated oxygen energy-loss spectrum is due to the 1s4f type transition. Our current DFT model fails to correctly cancel out the self-interaction energy leading to delocalization of the Ce 4f electrons which shifts the 4f levels down in energy. The simulate edge shape matches most of the predictions from other DFT methods seen in literature which show similar relative peak height trends [4]. Grain boundary structures were modelled using the method proposed by Braithwaite et al [5]. Our study has focused on the Σ3(210)/[001] symmetric tilt GB of stoichiometric CeO2 and the system was allowed to relax in three dimensions. Significant restructuring of the GB core was observed with atoms moving as much as 1 Å, as shown in Figure 2. To understand the electronic and local bonding changes associated with the GB, angular momentum site-projected density of states (DOS) was calculated for oxygen atoms at the bulk, the GB core and the GB side as depicted in F...

show abstract

supporting

confidence: 70%

Predicting the Electronic Structure of CeO₂ Grain Boundaries for Comparison with Atomic Resolution EELS

2017

View full text Add to dashboard Cite

show abstract

“…A ratio of the windowed integration over the edge and simultaneous subtracted background noise was utilized to determine the relative abundance of each element in the acquired core‐loss spectra . A multiple linear least squares peak fitting algorithm was performed, similar to the method employed by Aguiar et al ., to critique the changes in the near‐edge fine structure. The relative valence state of ions at the interface was determined using several methods including window integration and multiple linear peak fitting using the conjugate gradient method .…”

Section: Experimental Methodologymentioning

confidence: 99%

Thermal Expansion, Heat Capacity, and Thermal Conductivity of Nickel Ferrite (NiFe₂O₄)

et al. 2014

View full text Add to dashboard Cite

Nickel ferrite (NiFe 2 O 4 ) is major constituent of the oxide formed on the exterior of nuclear fuel cladding tubes during operation, which is comprised of corrosion products. Due to the impact of this oxide layer (typically referred to as CRUD) on the operation of commercial nuclear reactors, NiFe 2 O 4 has attracted interest. Although advances have been made in modeling CRUD nucleation and growth under a wide range of conditions, the thermophysical properties of NiFe 2 O 4 at high temperatures have only been approximated, thereby limiting the accuracy of such models. In this study, samples of NiFe 2 O 4 were synthesized in order to provide the thermal diffusivity, specific heat capacity, and thermal expansion data from room temperature to 1300K. These results were then used to determine thermal conductivity. Numerical fits are provided to facilitate ongoing modeling efforts. The Curie temperature determined through these measurements was in slight disagreement with literature values. Transmission electron microscopy investigation of multiple NiFe 2 O 4 samples revealed that minor nonstoichiometry was likely responsible for variations in the Curie temperature. However, these small changes in composition did not impact the thermal conductivity of NiFe 2 O 4 , and thus are not expected to play a large role * Corresponding Author

show abstract

“…Aguiar et al. have shown previously that this level of theory allows one to achieve qualitative agreement with experiment for such a sensitive probe of electronic structure as the electron energy loss spectra (EELS) for a variety of cubic oxides including urania …”

Section: Calculation Methodologymentioning

confidence: 93%

First‐Principles Molecular Dynamics Studies of Oxygen Sublattice Melting in Thoria

Szpunar

2016

J. Am. Ceram. Soc.

View full text Add to dashboard Cite

We apply first‐principles molecular dynamics to investigate the order–disorder transition in the oxygen sublattice, observed experimentally in thoria. The mean‐square displacements were calculated at high temperatures (2700 K–3660 K) and we demonstrate that oxygen atoms become mobile at 3000 K, while they stay confined at 2700 K. The rate of diffusion of oxygen atoms was calculated while for thorium atoms the mean‐square amplitudes of vibrations were evaluated. Thoria is predicted to exhibit a higher increase in thermal expansion with temperatures in the premelting region, similar to urania.

show abstract

Investigating the electronic structure of fluorite-structured oxide compounds: comparison of experimental EELS with first principles calculations

Cited by 9 publications

References 48 publications

Predicting the Electronic Structure of CeO₂ Grain Boundaries for Comparison with Atomic Resolution EELS

Predicting the Electronic Structure of CeO₂ Grain Boundaries for Comparison with Atomic Resolution EELS

Thermal Expansion, Heat Capacity, and Thermal Conductivity of Nickel Ferrite (NiFe₂O₄)

First‐Principles Molecular Dynamics Studies of Oxygen Sublattice Melting in Thoria

Contact Info

Product

Resources

About

Investigating the electronic structure of fluorite-structured oxide compounds: comparison of experimental EELS with first principles calculations

Cited by 9 publications

References 48 publications

Predicting the Electronic Structure of CeO2 Grain Boundaries for Comparison with Atomic Resolution EELS

Predicting the Electronic Structure of CeO2 Grain Boundaries for Comparison with Atomic Resolution EELS

Thermal Expansion, Heat Capacity, and Thermal Conductivity of Nickel Ferrite (NiFe2O4)

First‐Principles Molecular Dynamics Studies of Oxygen Sublattice Melting in Thoria

Contact Info

Product

Resources

About

Predicting the Electronic Structure of CeO₂ Grain Boundaries for Comparison with Atomic Resolution EELS

Predicting the Electronic Structure of CeO₂ Grain Boundaries for Comparison with Atomic Resolution EELS

Thermal Expansion, Heat Capacity, and Thermal Conductivity of Nickel Ferrite (NiFe₂O₄)