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Ionic Double Layers at the Surface of Magnesium‐Doped Aluminum Oxide: Effect on Segregation Properties
Author(s) -
Mukhopadhyay Sharmila M.,
Blakely Jack M.
Publication year - 1991
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.1151-2916.1991.tb07291.x
Subject(s) - ionic bonding , dopant , ion , arrhenius equation , magnesium , materials science , poisson's equation , doping , halide , oxide , enthalpy , chemistry , inorganic chemistry , thermodynamics , metallurgy , activation energy , physics , optoelectronics , organic chemistry , quantum mechanics
A model involving ionic double layers at the surface has been constructed for magnesia‐doped sapphire based on earlier models which were developed for cubic halides. The model takes into account the presence of electrostatic potentials, isolated point defects, defect complexes, and special surface sites which can act as sources and sinks for ions. Equations have been set up for the various defect concentrations, and Poisson's equation has been solved numerically to give depth profiles for defects and corresponding electric fields. The calculations suggest that Mg 2+ ions can segregate both to the free surface and to the space charge region. The effective (or Langmuir) enthalpy of segregation depends not only on the actual binding energies of the dopant ion, but also on other parameters such as the density of special surface sites. Over the temperature range studied, the variation of the calculated surface magnesium concentration with temperature is found to be approximately Arrhenius in nature, as was observed in segregation experiments.