Ab-initio calculation of yttrium substitutional impurities in {alpha}-Al{sub 2}O{sub 3}

Journal Article · Mon Dec 01 04:00:00 EST 1997 · Journal of the American Ceramic Society

OSTI ID:605765

Ching, W Y; Ruehle, M ^[1]; Xu, Y N ^[2]

---

1. Max-Planck Inst. fuer Metallforschung, Stuttgart (Germany)
2. Univ. of Missouri, Kansas City, MO (United States). Dept. of Physics

Yttrium has a very low solubility in bulk {alpha}-Al{sub 2}O{sub 3} and a great propensity for segregation to the grain boundaries in polycrystalline Al{sub 2}O{sub 3}. The segregation of yttrium influences many properties of the material. To understand the nature of the chemical bonding of yttrium within Al{sub 2}O{sub 3}, the authors have, as a first step, conducted an ab-initio self-consistent calculation for a yttrium impurity atom replacing an aluminum atom in Al{sub 2}O{sub 3}. They have used the first-principles orthogonalized linear combination of atomic orbitals (OLCAO) method and a supercell with 120 atoms in the hexagonal lattice. The relaxation of the nearby atoms, because of the presence of yttrium, is studied via total energy calculation within the local density approximation. The nearest-neighbor oxygen atoms of yttrium move outward by 8% and the next-nearest-neighbor aluminum atoms move inward by 5% of the respective separations in the undistorted lattice. A substitutional energy of 4.79 eV is obtained. The yttrium impurity introduces three defect states in the gap near the conduction band edge, thus naturally explaining the donor effect. Two of the defect states are degenerate, and all three are derived mainly from the Y 4d orbitals with very different local symmetries. The effective-charge and bond-order calculations show a substantial covalent bonding character between yttrium and the relaxed oxygen and aluminum atoms in the host.

• Sponsoring Organization: USDOE, Washington, DC (United States)
• DOE Contract Number: FG02-84ER45170
• OSTI ID: 605765
• Journal Information: Journal of the American Ceramic Society, Journal Name: Journal of the American Ceramic Society Journal Issue: 12 Vol. 80; ISSN 0002-7820; ISSN JACTAW
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM OXIDES
CRYSTAL DEFECTS
GRAIN BOUNDARIES
SEGREGATION
SOLUBILITY
YTTRIUM ADDITIONS