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First-principles characterization of the four phases of barium titanate Ghosez, Philippe ; ; in Ferroelectrics (1999), 220(1-2), 1-15 Using a first-principles approach, the four phases of perovskite barium titanate are studied. We determine the lattice parameter, the bulk modulus and the cohesive energy of the cubic phase; the relaxed ... [more ▼] Using a first-principles approach, the four phases of perovskite barium titanate are studied. We determine the lattice parameter, the bulk modulus and the cohesive energy of the cubic phase; the relaxed atomic positions in the three ferroelectric structures; and the evolution of the electronic properties from one phase to the other. The role of electronic exchange-correlation energy in the stabilization of the different phases is also investigated. [less ▲] Detailed reference viewed: 57 (0 ULg)Ab initio phonon dispersion curves and interatomic force constants of barium titanate Ghosez, Philippe ; ; in Ferroelectrics (1998), 206(1-4), 205-217 The phonon dispersion curves of cubic BaTiO3 have been computed within a first-principles approach and the results compared to the experimental data. The curves obtained are very similar to those reported ... [more ▼] The phonon dispersion curves of cubic BaTiO3 have been computed within a first-principles approach and the results compared to the experimental data. The curves obtained are very similar to those reported for KNbO3 by Yu and Krakauer (Phys. Rev. Lett., 74, 4067 (1995)). They reveal that correlated atomic displacements along [100] chains are at the origin of the ferroelectric instability. A simplified model illustrates that spontaneous collective displacements will occur when a dozen of aligned atoms are coupled. The longitudinal interatomic force constant between nearest neighbour Ti and O atoms is relatively weak in comparison to that between Ti atoms in adjacent cells. The small coupling between Ti and O displacements seems however necessary to reproduce a linear ferroelectric instability. [less ▲] Detailed reference viewed: 78 (3 ULg)Lattice dynamics and ferroelectric instability of barium titanate Ghosez, Philippe ; ; in Ferroelectrics (1997), 194 Using first-principles calculations, we investigate the lattice dynamics of cubic and rhombohedral BaTiO3 and rye discuss the origin of the structural instability of this ferroelectric material. First, we ... [more ▼] Using first-principles calculations, we investigate the lattice dynamics of cubic and rhombohedral BaTiO3 and rye discuss the origin of the structural instability of this ferroelectric material. First, we report results on the Born effective charges and the dielectric tensor and we emphasize the important reduction of these quantities in the ferroelectric phase, Then, the phonon frequencies at the Gamma point are calculated. We point out the similarity of theoretical eigenvectors in the cubic and rhombohedral phases. We examine the interaction of the vibration modes with the electric field and in particular the giant LO-TO splitting of the ferroelectric mode. Finally, separating the dipole-dipole interaction from the remaining short-range forces, we quantify the balance of forces leading to an unstable phonon in the cubic phase and we demonstrate its sensitivity to tiny effective charge changes. Within our decomposition, the stabilization of the unstable mode in the rhombohedral phase is produced by a reduction of the Born effective charges, while its stabilization under isotropic pressure is associated with a modification of the short-range forces. [less ▲] Detailed reference viewed: 111 (3 ULg)Role of the Coulomb interaction on the ferroelectric instability of Barium Titanate Ghosez, Philippe ; ; in Ferroelectrics (1996), 186 Detailed reference viewed: 6 (0 ULg)A microscopic study of barium titanate Ghosez, Philippe ; ; in Ferroelectrics (1995), 164 Detailed reference viewed: 9 (0 ULg)First-principles calculations of dielectric and effective charge tensors in Barium Titanate Ghosez, Philippe ; ; in Ferroelectrics (1994), 153 Detailed reference viewed: 17 (3 ULg) |
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