References of "Ghosez, Philippe"
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See detailScaling of structure and electrical properties in ultrathin epitaxial ferroelectric heterostructures
Nagarajan, V.; Junquera, J.; He, J. Q. et al

in Journal of Applied Physics (2006), 100

Scaling of the structural order parameter, polarization, and electrical properties was investigated in model ultrathin epitaxial SrRuO3/PbZr0.2Ti0.8O3/SrRuO3/SrTiO3 heterostructures. High-resolution ... [more ▼]

Scaling of the structural order parameter, polarization, and electrical properties was investigated in model ultrathin epitaxial SrRuO3/PbZr0.2Ti0.8O3/SrRuO3/SrTiO3 heterostructures. High-resolution transmission electron microscopy images revealed the interfaces to be sharp and fully coherent. Synchrotron x-ray studies show that a high tetragonality (c/a similar to 1.058) is maintained down to 50 angstrom thick films, suggesting indirectly that ferroelectricity is fully preserved at such small thicknesses. However, measurement of the switchable polarization (Delta P) using a pulsed probe setup and the out-of-plane piezoelectric response (d(33)) revealed a systematic drop from similar to 140 mu C/cm(2) and 60 pm/V for a 150 angstrom thick film to 11 mu C/cm(2) and 7 pm/V for a 50 angstrom thick film. This apparent contradiction between the structural measurements and the measured switchable polarization is explained by an increasing presence of a strong depolarization field, which creates a pinned 180 degrees polydomain state for the thinnest films. Existence of a polydomain state is demonstrated by piezoresponse force microscopy images of the ultrathin films. These results suggest that the limit for a ferroelectric memory device may be much larger than the fundamental limit for ferroelectricity. (c) 2006 American Institute of Physics. [less ▲]

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See detailFinite-size effects in BaTiO3 nanowires
Geneste, G.; Bousquet, Eric ULg; Junquera, J. et al

in Applied Physics Letters (2006), 88

The size dependence of the ferroelectric properties of BaTiO3 nanowires is studied from first principles. We show that the ferroelectric distortion along the wire axis disappears below a critical diameter ... [more ▼]

The size dependence of the ferroelectric properties of BaTiO3 nanowires is studied from first principles. We show that the ferroelectric distortion along the wire axis disappears below a critical diameter of about 1.2 nm. This disappearance is related to a global contraction of the unit cell resulting from low atomic coordinations at the wire surface. It is shown that a ferroelectric distortion can be recovered under appropriate tensile strain conditions. (c) 2006 American Institute of Physics. [less ▲]

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See detailDirect evidence for ferroelectric polar distortion in ultrathin lead titanate perovskite films
Despont, L.; Koitzsch, C.; Clerc, F. et al

in Physical Review. B, Condensed Matter and Materials Physics (2006), 73

X-ray photoelectron diffraction is used to directly probe the intracell polar atomic distortion and tetragonality associated with ferroelectricity in ultrathin epitaxial PbTiO3 films. Our measurements ... [more ▼]

X-ray photoelectron diffraction is used to directly probe the intracell polar atomic distortion and tetragonality associated with ferroelectricity in ultrathin epitaxial PbTiO3 films. Our measurements, combined with ab initio calculations, unambiguously demonstrate noncentrosymmetry in films a few unit cells thick, imply that films as thin as three unit cells still preserve a ferroelectric polar distortion, and also show that there is no thick paraelectric dead layer at the surface. [less ▲]

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See detailFirst-principles modeling of ferroelectric oxide nanostructures
Ghosez, Philippe ULg; Junquera, J.

in Handbook of theoretical and computational nanotechnology (2006)

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See detailUnusual behavior of the ferroelectric polarization in PbTiO3/SrTiO3 superlattices
Dawber, M.; Lichtensteiger, C.; Cantoni, M. et al

in Physical Review Letters (2005), 95

Artificial PbTiO3/SrTiO3 superlattices were constructed using off-axis rf magnetron sputtering. X-ray diffraction and piezoelectric atomic force microscopy were used to study the evolution of the ... [more ▼]

Artificial PbTiO3/SrTiO3 superlattices were constructed using off-axis rf magnetron sputtering. X-ray diffraction and piezoelectric atomic force microscopy were used to study the evolution of the ferroelectric polarization as the ratio of PbTiO3 to SrTiO3 was changed. For PbTiO3 layer thicknesses larger than the 3-unit cell SrTiO3 thickness used in the structure, the polarization is found to be reduced as the PbTiO3 thickness is decreased. This observation confirms the primary role of the depolarization field in the polarization reduction in thin films. For the samples with ratios of PbTiO3 to SrTiO3 of less than one, a surprising recovery of ferroelectricity that cannot be explained by electrostatic considerations was observed. [less ▲]

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See detailNonlinear optical susceptibilities, Raman efficiencies, and electro-optic tensors from first-principles density functional perturbation theory
Veithen, M.; Gonze, X.; Ghosez, Philippe ULg

in Physical Review. B, Condensed Matter and Materials Physics (2005), 71

The nonlinear response of infinite periodic solids to homogenous electric fields and collective atomic displacements is discussed in the framework of density functional perturbation theory. The approach ... [more ▼]

The nonlinear response of infinite periodic solids to homogenous electric fields and collective atomic displacements is discussed in the framework of density functional perturbation theory. The approach is based on the 2n+1 theorem applied to an electric-field-dependent energy functional. We report the expressions for the calculation of the nonlinear optical susceptibilities, Raman scattering efficiencies, and electro-optic (EO) coefficients. Different formulations of third-order energy derivatives are examined and their convergence with respect to the k-point sampling is discussed. We apply our method to a few simple cases and compare our results to those obtained with distinct techniques. Finally, we discuss the effect of a scissors correction on the EO coefficients and nonlinear optical susceptibilities. [less ▲]

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See detailTemperature dependence of the electro-optic tensor and refractive indices of BaTiO3 from first principles
Veithen, M.; Ghosez, Philippe ULg

in Physical Review. B, Condensed Matter and Materials Physics (2005), 71

We present a method to compute the temperature dependence of the refractive indices and electro-optic coefficients of ferroelectrics from a first-principles effective Hamiltonian and apply it to BaTiO3 in ... [more ▼]

We present a method to compute the temperature dependence of the refractive indices and electro-optic coefficients of ferroelectrics from a first-principles effective Hamiltonian and apply it to BaTiO3 in its tetragonal phase. We show that the effective Hamiltonian is a valid approach to study optical properties. We compare our formalism with the model of DiDomenico and Wemple and justify why the latter was successful, although its basic assumption is not met in practice. [less ▲]

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See detailFerroelectricity and tetragonality in ultrathin PbTiO3 films
Lichtensteiger, C.; Triscone, J. M.; Junquera, J. et al

in Physical Review Letters (2005), 94

The evolution of tetragonality with thickness has been probed in epitaxial c-axis oriented PbTiO3 films with thicknesses ranging from 500 down to 24 Angstrom. High resolution x ray pointed out a ... [more ▼]

The evolution of tetragonality with thickness has been probed in epitaxial c-axis oriented PbTiO3 films with thicknesses ranging from 500 down to 24 Angstrom. High resolution x ray pointed out a systematic decrease of the c-axis lattice parameter with decreasing film thickness below 200 Angstrom. Using a first-principles model Hamiltonian approach, the decrease in tetragonality is related to a reduction of the polarization attributed to the presence of a residual unscreened depolarizing field. It is shown that films below 50 Angstrom display a significantly reduced polarization but still remain ferroelectric. [less ▲]

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See detailA brief introduction to the ABINIT software project
Gonze, X.; Rignanese, G.-M.; Verstraete, Matthieu ULg et al

in Zeitschrift für Kristallographie (2005), 220

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See detailPhysique (J. Kane & M. Sternheim)
Ghosez, Philippe ULg; Hoebeke, Maryse ULg; Llabres, Gabriel ULg

Book published by Dunod - 3rd ed. (2004)

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

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 detailCritical thickness for ferroelectricity in perovskite ultrathin films
Junquera, J.; Ghosez, Philippe ULg

in Nature (2003), 422(6931), 506-509

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See detailFirst-principles calculation of the band offset at BaO/BaTiO3 and SrO/SrTiO3 interfaces
Junquera, J.; Zimmer, M.; Ordejon, P. et al

in Physical Review. B, Condensed Matter and Materials Physics (2003), 67

We report first-principles density-functional pseudopotential calculations on the atomic structures, electronic properties, and band offsets of BaO/BaTiO3 and SrO/SrTiO3 nanosized heterojunctions grown on ... [more ▼]

We report first-principles density-functional pseudopotential calculations on the atomic structures, electronic properties, and band offsets of BaO/BaTiO3 and SrO/SrTiO3 nanosized heterojunctions grown on top of a silicon substrate. The density of states at the junction does not reveal any electronic induced interface states. A dominant perovskite character is found at the interface layer. The tunability of the band offset with the strain conditions imposed by the substrate is studied. Using previously reported theoretical data available for Si/SrO, Si/BaO, SrTiO3/Pt, and BaTiO3/SrRuO3 interfaces we extrapolate the band alignments along two gate stacks of technological interest: Si/SrO/SrTiO3/Pt and Si/BaO/BaTiO3/SrRuO3 heterostructures. [less ▲]

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See detailLocal structure of liquid GeTe via neutron scattering and ab initio simulations
Raty, Jean-Yves ULg; Godlevsky, V. V.; Gaspard, Jean-Pierre ULg et al

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

We examine the local atomic order as well as some dynamic properties of the semiconducting liquid GeTe. We employ hot-neutron two-axis diffraction at three temperatures above the melting point and compare ... [more ▼]

We examine the local atomic order as well as some dynamic properties of the semiconducting liquid GeTe. We employ hot-neutron two-axis diffraction at three temperatures above the melting point and compare these results with ab initio molecular dynamics simulations. The simulations were based on interatomic forces derived from pseudopotentials constructed within density functional theory. At the melting temperature, the Peierls distortion responsible for the lower-temperature crystal phase is shown to manifest itself within the liquid structure. At higher temperatures in the liquid, increasing disorder in the Ge environment determines the eventual semiconductor-metal transition. The calculated kinematic viscosity of the liquid is found to agree with the experimental value and is shown to arise from the small diffusion coefficient of the Te atoms. [less ▲]

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See detailFirst-principles computation of material properties: the ABINIT software project
Gonze, X.; Beuken, J. M.; Caracas, R. et al

in Computational Materials Science (2002), 25(3), 478-492

The density functional theory (DFT) computation of electronic structure, total energy and other properties of materials, is a field in constant progress. In order to stay at the forefront of knowledge, a ... [more ▼]

The density functional theory (DFT) computation of electronic structure, total energy and other properties of materials, is a field in constant progress. In order to stay at the forefront of knowledge, a DFT software project can benefit enormously from widespread collaboration, if handled properly. Also, modern software engineering concepts can considerably ease its development. The ABINIT project relies upon these ideas: freedom of sources, reliability, portability, and self-documentation are emphasised, in the development of a sophisticated plane-wave pseudopotential code. We describe ABINITv3.0, distributed under the GNU General Public License. The list of ABINITv3.0 capabilities is presented, as well as the different software techniques that have been used until now: PERL scripts and CPP directives treat a unique set of FORTRAN90 source files to generate sequential (or parallel) object code for many different platforms; more than 200 automated tests secure existing capabilities; strict coding rules are followed; the documentation is extensive, including online help files, tutorials, and HTML-formatted sources. (C) 2002 Elsevier Science B.V. All rights reserved. [less ▲]

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See detailAb initio study of metal/ferroelectric and insulator/ferroelectric heterostructures
Zimmer, M.; Junquera, J.; Ghosez, Philippe ULg

in AIP Conference Proceedings (2002), 626

We report first-principles calculations on the structural properties of SrRuO 3/BaTiO3 (metal/ferroelectric) and BaO/BaTiO3 (insulator/ferroelectric) heterostructures, both of them paradigmatic systems ... [more ▼]

We report first-principles calculations on the structural properties of SrRuO 3/BaTiO3 (metal/ferroelectric) and BaO/BaTiO3 (insulator/ferroelectric) heterostructures, both of them paradigmatic systems for experimental measurements. Using a density-functional pseudopotential plane-wave method, as implemented in the ABINIT package, we have studied the changes in the interlayer spacing and the atomic rumpling. The substrates are explicitly considered in our simulations, so the lateral stress on the BaTiO3 thin films and mechanical boundary conditions are automatically taken into account. For the SrRuO3/BaTiO3 interface short-circuit boundary conditions are imposed. Results on free-standing BaTiO3 surfaces are also reported, showing good agreement with previous works. The ground state for all the structures studied here is paraelectric. [less ▲]

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See detailElectron localization in lithium niobate
Veithen, M.; Ghosez, Philippe ULg

in AIP Conference Proceedings (2002), 626

Using a plane-wave pseudopotential approach to density functional theory, we investigate the degree of electron localization in lithium niobate. We pay a particular attention to its variation during the ... [more ▼]

Using a plane-wave pseudopotential approach to density functional theory, we investigate the degree of electron localization in lithium niobate. We pay a particular attention to its variation during the phase transition and to the relationship with the electronic structure and the Born effective charges in this material. A band-by-band decomposition allows us to focus on the different bands composing the energy spectrum of this compound. At variance with previous calculations based on finite differences, the localization tensor has been obtained using linear-response techniques. [less ▲]

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See detailElectron localization: Band-by-band decomposition and application to oxides
Veithen, M.; Gonze, X.; Ghosez, Philippe ULg

in Physical Review. B, Condensed Matter and Materials Physics (2002), 66

Using a plane-wave pseudopotential approach to density functional theory we investigate the electron localization length in various oxides. For this purpose, we first set up a theory of the band-by-band ... [more ▼]

Using a plane-wave pseudopotential approach to density functional theory we investigate the electron localization length in various oxides. For this purpose, we first set up a theory of the band-by-band decomposition of this quantity, more complex than the decomposition of the spontaneous polarization (a related concept), because of the interband coupling. We show its interpretation in terms of Wannier functions and clarify the effect of the pseudopotential approximation. We treat the case of different oxides: BaO, alpha-PbO, BaTiO3, and PbTiO3. We also investigate the variation of the localization tensor during the ferroelectric phase transitions of BaTiO3 as well as its relationship with the Born effective charges. [less ▲]

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

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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