Cation Solute Segregation to Surfaces of MgO and α-Al2O3

Abstract

ABSTRACTLow energy ion scattering spectroscopy (LEIS) and Auger electron spectroscopy (AES) were used to measure the extent of impurity cation solute segregation to MgO (100) and various surfaces of single and polycrystalline Al2O3, following equilibration anneals at temperatures above 1000°C in ulfra-high vacuum. Systems studied include Ca/MgO, Ni/MgO, Ca/A12O3 and Y/Al2O3. Calcium segregation to MgO (100) is reversible and exhibits monofayer adsorption behavior with an enthalpy of segregation of approximately -55 kJ/mole with maximum occupation of surface cation sites approaching 40%. Nickel segregation to MgO(100) is masked by a preferential segregation of calcium. Calcium segregation to A12O3 surfaces has been found to be transient with a maximum surface cation site occupation of less than 10% as determined by LEIS and estimated enthalpy of segregation in the range -go to -190 kJ/mole. Yttrium segregation to surfaces of a polycrystalline Al2O3 compact was limited by competing calcium segregation at temperatures be ow 1600°C. An estimated enthalpy of segregation for yttrium to A12O3 surfaces was in the range -23 to -43 kJ/mole, with maximum cation surface site occupation of about 15%. Practical limitations to free surface measurements of solute segregation in these materials are discussed.