Effect of Yttrium and Erbium Ions on Epitaxial Phase Transformations in Alumina

The effect of low concentrations of Y, Er, and Cr solutes on the amorphous-to-γ transformation and on the γ-to-α transformation in aluminum oxide has been studied in situ by time-resolved reflectivity. The activation energies of the two transformations with these dopants are the same as in undoped alumina, being 4.1 ± 0.1 and 5.2 ± eV, respectively. Although not affecting the activation energies, Y, Er, and Cr do affect the transformation kinetics. Y and Cr ions decrease the γ-to-α transformation velocity and, over the limited range studied, do so in proportion to their concentration. Concentrations of Er as low as ∼6 ppm retard the γ-to-α transformation and concentrations of 32 ppm essentially stop the transformation occurring within the times and temperatures accessible within the present experiment, thereby preventing quantification of the effect of Er on the α-phase transformation. Erbium also retards the amorphous-to-γ transformation relative to undoped alumina whereas yttrium and chromium accelerate it.