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Peer Reviewed
See detailFirst-Principles Study of Phase Transitions in Silicon Nitride at High Pressure
Xu, Bin ULiege; Dong, Jianjun; Shebanova, Olga et al

Poster (2009, June)

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See detailFirst-principles study of structural and vibrational properties of SrZrO3
Amisi, Safari ULiege; Bousquet, Eric ULiege; Katcho, Karume et al

in Physical Review. B, Condensed Matter and Materials Physics (2012), 85

Using first-principles calculations, we investigate the electronic, structural, and vibrational properties of SrZrO3. We start from the high-symmetry cubic perovskite phase, for which the phonon ... [more ▼]

Using first-principles calculations, we investigate the electronic, structural, and vibrational properties of SrZrO3. We start from the high-symmetry cubic perovskite phase, for which the phonon dispersion curves are reported.We point out the coexistence of structural antiferrodistortive instabilities at the R and M zone-boundary points and a ferroelectric instability at the zone center.We showthat the strong antiferrodistortive motions suppress ferroelectricity and are responsible for the orthorhombic ground state as in CaTiO3. The structural properties <br />of possible intermediate phases and of the orthorhombic Pnma ground state are reported. For the latter, an assignment of IR and Raman zone-center phonon modes is proposed. The main features of the ferroelectric instability are also discussed, and we show that a ferroelectric ground state can even be induced in SrZrO3 by strain engineering. [less ▲]

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See detailFirst-principles study of the dielectric and dynamical properties of lithium niobate
Veithen, M.; Ghosez, Philippe ULiege

in Physical Review. B, Condensed Matter and Materials Physics (2002), 65

Using a first-principles approach based on density-functional theory, the electronic, dielectric, and dynamical properties of the two phases of lithium niobate are studied. In particular, the spontaneous ... [more ▼]

Using a first-principles approach based on density-functional theory, the electronic, dielectric, and dynamical properties of the two phases of lithium niobate are studied. In particular, the spontaneous polarization, the optical dielectric tensors, the Born effective charges, and the zone-center phonons are computed. The Born effective charges are found to be significantly larger than the nominal ionic charges of the ions, a feature similar to what is observed in related ABO(3) compounds and attributed to the hybridization between the O 2p and Nb 4d states. The analysis of the zone-center phonons in the paraelectric phase reveals an unstable A(2u) mode to be responsible for the phase transition. The origin of the structural instability is attributed to destabilizing long-range dipolar interactions, which are not fully compensated by stabilizing short-range forces. Finally, the identification of the E modes in the ferroelectric phase, which is still the cause for debates in spite of the numerous experimental and theoretical studies, is discussed and an assignation based on the analysis of the mode-oscillator strengths and the angular dispersion relation of extraordinary phonons is proposed. [less ▲]

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See detailFirst-principles study of the dielectric and dynamical properties of orthorhombic CaMnO3
Bhattacharjee, Satadeep; Bousquet, Eric ULiege; Ghosez, Philippe ULiege

in Journal of Physics : Condensed Matter (2008), 20

The structural, dielectric and dynamical properties of the low temperature antiferromagnetic orthorhombic phase of CaMnO3 have been computed from first principles, using a density functional theory ... [more ▼]

The structural, dielectric and dynamical properties of the low temperature antiferromagnetic orthorhombic phase of CaMnO3 have been computed from first principles, using a density functional theory approach within the local spin density approximation. The theoretical structural parameters are in good agreement with experiment. The full set of zone-center phonons is reported, allowing new assignment of experimental Raman data and providing reference values for the interpretation of future infrared phonon measurements. It is shown that the static dielectric constant is very large and comparable in amplitude to that of isostructural CaTiO3. In contrast to the pseudocubic structure, it is also highly anisotropic. These features are discussed in relationship to the anomalous Born effective charges and the presence of low frequency polar modes. [less ▲]

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See detailFirst-principles study of the dynamical and nonlinear optical properties of urea single crystals
Hermet, Patrick ULiege; Ghosez, Philippe ULiege

in Physical Chemistry Chemical Physics [=PCCP] (2010), 12

Raman and infrared spectra of urea single crystals have been calculated using the density functional theory. This allowed us to assign the remaining experimental low-frequency phonon modes. Then, we have ... [more ▼]

Raman and infrared spectra of urea single crystals have been calculated using the density functional theory. This allowed us to assign the remaining experimental low-frequency phonon modes. Then, we have determined the sign of the second-harmonic nonlinear optical susceptibility coefficient in urea to be negative, clarifying a long debate in the literature. Finally, we computed for the first time the electro-optic coefficients of urea. We found that the electronic and ionic contributions have a similar order of magnitude and an opposite sign, yielding a smaller value than that expected, and necessitating further experimental clarifications. [less ▲]

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See detailFirst-principles study of the electro-optic effect in ferroelectric oxides
Veithen, M.; Gonze, X.; Ghosez, Philippe ULiege

in Physical Review Letters (2004), 93

We first present a method to compute the electro-optic tensor from first principles, explicitly taking into account the electronic, ionic and piezoelectric contributions. We then study the nonlinear optic ... [more ▼]

We first present a method to compute the electro-optic tensor from first principles, explicitly taking into account the electronic, ionic and piezoelectric contributions. We then study the nonlinear optic behavior of three paradigmatic ferroelectric oxides. Our calculations reveal the dominant contribution of the soft mode to the electro-optic coefficients in LiNbO3 and BaTiO3 and its minor role in PbTiO3. We identify the coupling between the electric field and the polar atomic displacements along the B-O chains as the origin of the large electro-optic response in perovskite ABO(3) compounds. [less ▲]

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See detailFirst-principles study of the ferroelectric Aurivillius phase Bi2WO6
Djani-Ait, Hania ULiege; Bousquet, Eric ULiege; Kellou, Abdelhafid et al

in Physical Review. B, Condensed Matter and Materials Physics (2012), 86

In order to better understand the reconstructive ferroelectric-paraelectric transition of Bi2WO6, which is unusual within the Aurivillius family of compounds, we performed first-principles calculations of ... [more ▼]

In order to better understand the reconstructive ferroelectric-paraelectric transition of Bi2WO6, which is unusual within the Aurivillius family of compounds, we performed first-principles calculations of the dielectric and dynamical properties of two possible high-temperature paraelectric structures—the monoclinic phase of A2/m symmetry observed experimentally and the tetragonal phase of I4/mmm symmetry—common to most Aurivillius-phase components. Both paraelectric structures exhibit various unstable modes, which, after their condensation, bring the system toward more stable structures of lower symmetry. The calculations confirm that, starting from the paraelectric A2/m phase at high temperatures, the system must undergo a reconstructive transition to reach the P21ab ferroelectric ground state. [less ▲]

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See detailFirst-principles study of the lattice dynamical properties of strontium ruthenate
Miao, Naihua ULiege; Bristowe, Nicholas ULiege; Xu, Bin et al

in Journal of Physics : Condensed Matter (2014), 26

By means of first-principles calculations, various properties of SrRuO3 are investigated, focusing on its lattice dynamical properties. Despite having a Goldschmidt tolerance factor very close to 1, the ... [more ▼]

By means of first-principles calculations, various properties of SrRuO3 are investigated, focusing on its lattice dynamical properties. Despite having a Goldschmidt tolerance factor very close to 1, the phonon dispersion curves of the high-temperature cubic phase of SrRuO3 show strong antiferrodistortive instabilities. The energetics of metastable phases with different tilt patterns are discussed, concluding that the coupling of oxygen rotation modes with anti-polar Sr motion plays a key role in stabilizing the Pnma phase with respect to alternative rotation patterns. Our systematic analysis confirms previous expectations and contributes to rationalizing better why many ABO3 perovskites, including metallic compounds, exhibit an orthorhombic ground state. The zone-center phonon modes of the Pnma phase have been computed, from which we propose partial reassignment of available experimental data. The full dispersion curves have also been obtained, constituting benchmark results for the interpretation of future measurements and providing access to thermodynamical properties. [less ▲]

Detailed reference viewed: 116 (11 ULiège)
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See detailFirst-Principles Study of the Mechanism for B4-to-B1 Phase Transformation in AlN
Xu, Bin ULiege; Dong, Jianjun; Stokes, Harold et al

Poster (2009, June)

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See detailFirst-Principles Study of the Thermoelectric Properties of SrRuO3
Miao, Naihua; Xu, Bin ULiege; Bristowe, Nicholas ULiege et al

in Journal of Physical Chemistry (2016), 120

Detailed reference viewed: 168 (5 ULiège)
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See detailFirst-Principles Study of Thermal and Elastic Properties of Al2O3
Xu, Bin ULiege; Dong, Jianjun

Poster (2007, February)

Detailed reference viewed: 32 (3 ULiège)
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See detailFirst-principles study of thermoelectric properties in SrTiO3 and FeSb2
Xu, Bin ULiege; Diakhate, Momar ULiege; Verstraete, Matthieu ULiege et al

Poster (2011, October)

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See detailFirst-principles study of transport properties in Os and OsSi
Xu, Bin ULiege; Verstraete, Matthieu ULiege

in Physical Review. B : Condensed Matter (2013), 87

Detailed reference viewed: 109 (9 ULiège)
See detailFirst-principles study of tungsten trioxide: Structural properties and polaron formation
Hamdi, Hanen ULiege

Doctoral thesis (2017)

Using first-principles calculations, we analyze the structural properties of tungsten trioxide WO3. Our calculations rely on density functional theory and the use of the B1-WC hybrid functional, which ... [more ▼]

Using first-principles calculations, we analyze the structural properties of tungsten trioxide WO3. Our calculations rely on density functional theory and the use of the B1-WC hybrid functional, which provides very good agreement with experimental data. We show that the hypothetical high-symmetry cubic reference structure combines several ferroelectric and antiferrodistortive (antipolar cation motions, rotations and tilts of oxygen octahedra) structural instabilities. Although the ferroelectric instability is the largest, the instability related to antipolar W motions combines with those associated to oxygen rotations and tilts to produce the biggest energy reduction, yielding a P2_1/c ground state. This non-polar P2_1/c phase is only different from the experimentally reported Pc ground state by the absence of a very tiny additional ferroelectric distortion. The calculations performed on a stoichiometric compound so suggest that the low temperature phase of WO3 is not intrinsically ferroelectric and that the {experimentally observed} ferroelectric character might arise from extrinsic defects such as oxygen vacancies. Independently, we also identify never observed R3m and R3c ferroelectric metastable phases with large polarizations and low energies close to the P21/c ground state, which makes WO3 a potential antiferroelectric material. The relative stability of various phases is discussed in terms of the anharmonic couplings between different structural distortions, highlighting a very complex interplay. On the second hand, the addition of a single electron to the largest supercell of the monoclinic P21/c ground state of WO3 causes the development of a medium polaron inside of this material. We then study and characterize a medium polaron formation in WO3 from first-principles calculation. We show how the medium polaron in the supercell of WO3 can change its structural, electronic and dynamical properties. [less ▲]

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See detailFirst-principles study of vibrational and noncollinear magnetic properties of the perovskite to postperovskite pressure transition of $NaMnF_3$
Garcia Castro, Andrés Camilo ULiege; Romero, A. H.; Bousquet, Eric ULiege

in Physical Review. B, Condensed Matter and Materials Physics (2014), 90

We performed a first-principles study of the structural, vibrational, electronic, and magnetic properties of NaMnF3 under applied isotropic pressure. We found that NaMnF3 undergoes a reconstructive phase ... [more ▼]

We performed a first-principles study of the structural, vibrational, electronic, and magnetic properties of NaMnF3 under applied isotropic pressure. We found that NaMnF3 undergoes a reconstructive phase transition at 8 GPa from the Pnma distorted perovskite structure toward the Cmcm postperovskite structure. This is confirmed by a sudden change of the Mn-F-Mn bondings where the crystal goes from corner-shared octahedra in the Pnma phase to edge-shared octahedra in the Cmcm phase. The magnetic ordering also changes from a G-type antiferromagnetic ordering in the Pnma phase to a C-type antiferromagnetic ordering in the Cmcm phase. Interestingly, we found that the high-spin d-orbital filling is kept at the phase transition which has never been observed in the known magnetic postperovskite structures. We also found a highly noncollinear magnetic ordering in the Cmcm postperovskite phase that drives a large ferromagnetic canting of the spins. We discuss the validity of these results with respect to the U and J parameters of the GGA+U exchange-correlation functional used in our study and conclude that large-spin canting is a promising property of the postperovskite fluoride compounds. [less ▲]

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See detailFirst-Principles Study on the Lattice Dynamics and Thermoelectric Properties of Materials
Miao, Naihua ULiege

Doctoral thesis (2015)

Thermoelectricity has been regarded as one of the most promising strategies for clean, low-cost and environmental friendly sustainable energy for several decades. Perovskite oxides, like SrRuO3, are ... [more ▼]

Thermoelectricity has been regarded as one of the most promising strategies for clean, low-cost and environmental friendly sustainable energy for several decades. Perovskite oxides, like SrRuO3, are considered as a potential thermoelectric material for low-cost and large-scale thermoelectric applications due to their good thermal and chemical stability in a wide temperature range, great flexibility for structural and compositional manipulating, and environmental friendliness. This thesis is devoted to a theoretical study of the lattice dynamics and thermoelectric properties of materials, like SrRuO3 perovskite and MgAgSb-based materials. Firstly, to obtain insight into the lattice dynamics of the SrRuO3, the phonon-related properties are presented and contributes to rationalize better why many ABO3 perovskites, including metallic compounds, exhibit an orthorhombic ground state. Then the thermoelectric properties of SrRuO3 are investigated by combining first-principles calculations and Boltzmann transport theory, revealing the relationship between the exchange-correlation functionals and the thermoelectric quantities. Furthermore, based on the first-principles calculations, effective model potentials for SrRuO3 are constructed providing access to the finite-temperature properties and phase-transitions. Additionally, the electronic structure and thermoelectric properties of a class of new emerging MgAgSb-based materials, which are promising for room-temperature thermoelectric applications, are also studied and the optimization strategies are proposed for the improvement of thermoelectric performance. [less ▲]

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See detailLe fisc peut-il ou doit-il prendre en considération l'origine légale ou morale des revenus imposables?
Richelle, Isabelle ULiege

Article for general public (2015)

Le fisc taxe des revenus illicites ou immoraux, mais qu'en est'il de la déductibilité frais de telle nature lorsqu'ils sont supportés en vue d'acquérir ou de conserver des revenus imposables?

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See detailFiscaal compendium: Internationaal fiscaal recht
Peeters, Bart ULiege; Bammens, Niels; Reypens, Nathalie

Book published by Wolters Kluwer (2016)

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See detailFiscal decentralization and the performance of higher education institutions: The case of Europe
Jacqmin, Julien ULiege

Scientific conference (2017, March 30)

Detailed reference viewed: 18 (2 ULiège)