Anomalous effective charges and far IR optical absorption of Al$_2$Ru from first principles

Serdar Ogut; Karin M. Rabe

doi:10.1103/physrevb.54.r8297

Home/Archive/arXiv

arXiv · mtrl-th/9608004

Anomalous effective charges and far IR optical absorption of Al$_2$Ru from first principles

Serdar Ogut·Karin M. Rabe

View original source ↗Read source document ↗Export metadata ↓

Abstract

For the orthorhombic intermetallic semiconductor Al$_2$Ru, the bandstructure, valence charge density, zone center optical phonon frequencies, and Born effective charge and electronic dielectric tensors are calculated using variational density functional perturbation theory with {\em ab initio} pseudopotentials and a plane wave basis set. Good agreement is obtained with recent measurements on polycrystalline samples which showed anomalously strong far IR absorption by optical phonons, while analysis of the valence charge density shows that the static ionic charges of Al and Ru are negligible. Hybridization is proposed as the single origin both of the semiconducting gap and the anomalous Born effective charges. Analogous behavior is expected in related compounds such as NiSnZr, PbTe, skutterudites, and Al-transition-metal quasicrystals.

Explore related subjects

mtrl-th cond-mat.mtrl-sci

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

Serdar Ogut, Karin M. Rabe. 1996-08-13. Anomalous effective charges and far IR optical absorption of Al$_2$Ru from first principles. https://doi.org/10.1103/physrevb.54.r8297

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv1997

Ab initio molecular dynamics study of the desorption of D_2 from Si(100)

Ab initio molecular dynamics calculations of deuterium desorbing from Si(100) have been performed in order to monitor the energy redistribution among the various D$_2$ and silicon degrees of freedom during the desorption process. The calculations show that a considerable part of the potential energy at the transition state to desorption is transferred to the silicon lattice. The deuterium molecules leave the surface vibrationally hot and rotationally cold, in agreement with thermal desorption experiments; the mean kinetic energy, however, is larger than found in a laser-induced desorption experiment. We discuss possible reasons for this discrepancy.

mtrl-th↗

arXiv1997

Surface Effects in Ferroelectrics: Periodic Slab Computations for BaTiO_3

Total energies, electronic structure, surface energies, polarization, potentials and charge densities were studied for slabs of BaTiO_3 using the Linearized Augmented Plane Wave (LAPW) method. The depolarization field inhibits ferroelectricity in the slabs, and the macroscopic field set up across a ferroelectric slab is sufficient to cause electronic states to span the gap and give a metallic band structure, but the band shifts are not rigid and O p states tend to pile up at the Fermi level. There are electronic surface states, especially evident on TiO_2 surfaces. The dangling bonds bond back to the surface Ti's and make the surface stable and reactive. The BaO surfaces are more ionic than the bulk.

mtrl-th↗

arXiv1996

Effects of crack tip geometry on dislocation emission and cleavage: A possible path to enhanced ductility

We present a systematic study of the effect of crack blunting on subsequent crack propagation and dislocation emission. We show that the stress intensity factor required to propagate the crack is increased as the crack is blunted by up to thirteen atomic layers, but only by a relatively modest amount for a crack with a sharp 60$^\circ$ corner. The effect of the blunting is far less than would be expected from a smoothly blunted crack; the sharp corners preserve the stress concentration, reducing the effect of the blunting. However, for some material parameters blunting changes the preferred deformation mode from brittle cleavage to dislocation emission. In such materials, the absorption of preexisting dislocations by the crack tip can cause the crack tip to be locally arrested, causing a significant increase in the microscopic toughness of the crack tip. Continuum plasticity models have shown that even a moderate increase in the microscopic toughness can lead to an increase in the macroscopic fracture toughness of the material by several orders of magnitude. We thus propose an atomic-scale mechanism at the crack tip, that ultimately may lead to a high fracture toughness in some materials where a sharp crack would seem to be able to propagate in a brittle manner. Results for blunt cracks loaded in mode II are also presented.

mtrl-th↗