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Equilibrium Shape of Internal Cavities in Sapphire

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The equilibrium shape of internal cavities in sapphire was determined through the study of submicrometer internal cavities in single crystals. Cavities formed from indentation cracks during annealing at 1600°C. Equilibrium could be reached only for cavities that were smaller than is approximately100 nm. Excessive times were required to achieve equilibrium for cavities larger than is approximately 1m. Five equilibrium facet planes were observed to bound the cavities: the basal (C) {0001}, rhombohedral (R) {1¯012}, prismatic (A) {12¯10}, pyramidal (P) {112¯3}, and structural rhombohedral (S) {101¯1}. The surface energies for these planes relative to the surface energy of the basal plane were R = 1.05, A = 1.12, P = 1.06, S = 1.07. These energies were compared with the most recent theoretical calculations of the surface energy of sapphire. The comparison was not within experimental scatter for any of the surfaces, with the measured relative surface energies being lower than the calculated energies. Although the prismatic (M) {101¯0} planes are predicted to be a low-energy surface, facets of this orientation were not observed.
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Document Type: Research Article

Affiliations: 1: Department of Inorganic Materials Engineering, Seoul National University, Seoul, 151-742, Korea 2: National Institute of Standards and Technology, Gaithersburg, Maryland 20899

Publication date: 1997-01-01

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