Polymorphic basal twin boundaries and anisotropic growth in {alpha}-Al{sub 2}O{sub 3}

Journal Article · Wed Feb 01 04:00:00 EST 1995 · Acta Metallurgica et Materialia

DOI:https://doi.org/10.1016/0956-7151(94)00276-N· OSTI ID:27909

Kaplan, W D; Brandon, D G ^[1]; Kenway, P R ^[2]

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1. Technion, Haifa (Israel). Dept. of Materials Engineering
2. Max-Planck-Inst. fuer Metallforschung, Stuttgart (Germany)

High resolution transmission electron microscopy (HRTEM) was used to study the structure of annealing twins in {alpha}-Al{sub 2}O{sub 3}. A basal twin was found where each of the two twin boundaries with the matrix had a different two-dimensional structure. The energies of alternative twin boundary structures were calculated using an ionic model. The relative difference in the energy of the boundary structures is appreciable, and the relative energies of steps at the boundary required for twin formation and termination show large differences for opposite growth directions in the basal plane. This suggest that the different twin boundary structures are the result of anisotropic growth of alumina, which is related to the lack of centro-symmetry in the trigonal corundum structure. The model is important for an understanding of annealing twin formation and growth mechanisms in sapphire, and could be extended to predict anisotropic growth phenomena for other non-centro-symmetric structures.

• OSTI ID: 27909
• Journal Information: Acta Metallurgica et Materialia, Journal Name: Acta Metallurgica et Materialia Journal Issue: 2 Vol. 43; ISSN 0956-7151; ISSN AMATEB
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM OXIDES
ANISOTROPY
CRYSTAL MODELS
CRYSTAL STRUCTURE
GRAIN BOUNDARIES
GRAIN GROWTH
MICROSTRUCTURE
TWINNING