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Abstract
Auger electron spectroscopy (AES) and low‐energy electron diffraction (LEED) were used to study the segregation of Mg to the surface of a sapphire crystal doped with 40 ppm of Mg. In situ vacuum annealing and AES measurements at 900° to =1800°C failed to reveal Mg segregation on the (0001) plane above the detectability limit of the cylindrical mirror analyzer. However, when identical crystals were placed together to simulate a “closed system” and annealed in air, surface segregation of Me was detected above 1200°C. The variation of the equilibrium surface concentration of Mg with temperature in the range 1300° to =1500°C, gave an effective Langmuir heat Of segregation of Mg of =–146 kJ/mol. Evidence for the formation of a two‐dimensional ordered structure on the sapphire surface was also obtained through LEED studies. The implications of these segregation results for our understanding of the sintering behavior of magnesia‐doped alumina are discussed.
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