Crystallization of pseudo-orthorhombic anorthite on basal sapphire

Journal Article · Fri Jan 01 04:00:00 EST 1999 · Journal of the American Ceramic Society

DOI:https://doi.org/10.1111/j.1151-2916.1999.tb01720.x· OSTI ID:316019

Mallamaci, M P; Carter, C B ^[1]

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1. Univ. of Minnesota, Minneapolis, MN (United States). Dept. of Chemical Engineering and Materials Science

Anorthite-glass films were grown on basal Al{sub 2}O{sub 3} substrates using pulsed-laser deposition. The substrates were cleaned and annealed in air at 1400 C to produce crystallographically flat (0001) terraces. The films were deposited in an oxidizing environment. X-ray microanalysis confirmed the composition of the glass films to be close to that of anorthite (CaO{center_dot}Al{sup 2}O{sub 3}{center_dot}2SiO{sub 2}). Although anorthite usually has triclinic symmetry, subsequent crystallization of these films in air at 1200 C resulted in the formation of pseudo-orthorhombic CaAl{sub 2}Si{sub 2}O{sub 8} (o-anorthite), a known metastable form of the mineral. Microstructural characterization was performed using visible-light microscopy, scanning electron microscopy, and transmission electron microscopy. The films dewetted the substrate either before or after crystallization to form o-anorthite islands which had strong orientation relationships to the Al{sub 2}O{sub 3} substrate. The epitaxy of the o-anorthite islands was accompanied by a small lattice mismatch parallel to the substrate plane. The formation of three orientational variants is consistent with the symmetry of the basal Al{sup 2}O{sub 3} surface. The dislocation network observed at the o-anorthite/Al{sub 2}O{sub 3} interface indicates that nucleation and growth of the anorthite occurs directly on the substrate surface without an intervening interfacial amorphous layer. The study of anorthite-glass films is important because they are present in liquid-phase-sintered Al{sub 2}O{sub 3}, and may be devitrified by postsintering heat treatments.

• Sponsoring Organization: USDOE, Washington, DC (United States)
• DOE Contract Number: FG02-92ER45465
• OSTI ID: 316019
• Journal Information: Journal of the American Ceramic Society, Journal Name: Journal of the American Ceramic Society Journal Issue: 1 Vol. 82; ISSN 0002-7820; ISSN JACTAW
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ANORTHITE
CRYSTALLIZATION
DISLOCATIONS
ELECTRON MICROSCOPY
ENERGY BEAM DEPOSITION
FILMS
GLASS
LASERS
SAPPHIRE