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Determination of Pipe Diffusion Coefficients in Undoped and Magnesia‐Doped Sapphire (α‐Al 2 O 3 ): A Study Based on Annihilation of Dislocation Dipoles
Author(s) -
Tang Xiaohong,
Lagerlöf K. Peter D.,
Heuer Arthur H.
Publication year - 2003
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.2003.tb03341.x
Subject(s) - sapphire , materials science , dislocation , dipole , annealing (glass) , doping , crystallography , annihilation , condensed matter physics , analytical chemistry (journal) , composite material , chemistry , optics , optoelectronics , physics , nuclear physics , laser , organic chemistry , chromatography
The breakup of dislocation dipoles in plastically deformed samples of undoped and 30‐ppm‐MgO‐doped sapphire (α‐Al 2 O 3 ) was monitored using conventional TEM techniques. Dislocation dipoles break up into prismatic dislocation loops in a sequential process during annealing; i.e., dislocation loops are pinched off at the end of a dislocation dipole. This pinch‐off process is primarily controlled by pipe diffusion, and pipe diffusion coefficients at temperatures between 1300° and 1500°C were estimated by monitoring the kinetics of the dipole breakup process. We determined D P U = 8.1( –4.3 +9.1 ) × 10 –3 exp [–(4.5 ± 1.3 eV )/ kT )] m 2 /s for the undoped material. The pipe diffusion kinetics for the MgO‐doped crystal was determined at 1250° and 1300°C and was about 6 times higher than for undoped sapphire. Finally, climb dissociation of the dislocations constituting the perfect dipoles in sapphire is common; annihilation of one set of partials can result in the formation of faulted dipoles, which can pinch off to form faulted dislocation loops. D P U for faulted dipoles in the undoped material was determined at 1300° and 1350°C, and was about 4–10 times higher than for perfect dipoles.