Equilibrium Shape of Internal Cavities in Sapphire

• Published in: Journal of the American Ceramic Society Vol. 80; no. 1; pp. 62 - 68
• Main Authors: Choi, Jung-Hae, Kim, Doh-Yeon, Hockey, Bernard J., Wiederhorn, Sheldon M., Handwerker, Carol A., Blendell, John E., Carter, W. Craig, Roosen, Andrew R.
• Format: Journal Article
• Language: English
• Published: Westerville, Ohio American Ceramics Society 01-01-1997; Blackwell
• Subjects: Approximation; Condensed matter: structure, mechanical and thermal properties; Defects and impurities in crystals; microstructure; Exact sciences and technology; Gallium; Holes; Indentation; Mathematical analysis; Microscopic defects (voids, inclusions, etc.); Physics; Planes; Sapphire; Structure of solids and liquids; crystallography; Surface energy; Crystal defects; Inorganic compounds; Equilibrium shape; Theoretical study; Binary compounds; Computerized simulation; High temperature; Experimental study; Indentation; Faceting; Cavities; Cracks; Sapphire; Thermal annealing; TEM; Surface energy; Aluminium oxides
• ISSN: 0002-7820; 1551-2916
• DOI: 10.1111/j.1151-2916.1997.tb02791.x

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 1μm. 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 γR = 1.05, γA = 1.12, γP = 1.06, γS = 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.