Ion‐Probe Measurement of Oxygen Self‐Diffusion in Single‐Crystal Al ₂ O ₃

Anion self‐diffusion coefficients normal to (1102) were obtained for single‐crystal Al 2 O 3 in a 1.3 × 10 3 N/m 2 (10 −5 torr) vacuum at 1585° to 1840°C. Tracer was supplied from an initial 650 to 1300 A Al 2 18 O 3 layer produced by the oxidation of vapor‐deposited Al metal films in an 18 O 2 atmosphere at 520°C. Concentration gradients extended over depths of 3000 to 5000 A and were measured by mass spectrometry of material sputtered from the samples with a beam of Ar + ions. Crystals which had not been preannealed to remove surface damage displayed enhanced diffusion. Diffusion coefficients from preannealed crystals may be described by D 0 =6.4×10 5 cm 2 /s, with an activation energy of 188 ± 7 kcal/mol. The diffusion is interpreted as an extrinsic vacancy mechanism.