Calcium Segregation to a Magnesium Oxide (100) Surface

Abstract

The segregation of calcium to a (100) cleavage surface of an MgO crystal, with bulk calcium concentration of 200 ppm was measured in situ at T =900° to 1450°C in ultrahigh vacuum, using Auger and low‐energy ion‐scattering spectroscopies. A measured heat of segregation of approximately ‐50.3 kJ/mol (‐12 kcal/mol) is in favorable agreement with a value of ‐58.7 kJ/mol (‐14 kcal/mol) determined using solute strain energy and surface free energy criteria. The equilibrium value for the calcium segregation between 950° and 1000°C is estimated to correspond to a 20% occupation of the surface cation sites.