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-gamma transformation and on the gamma-to-alpha transformation in aluminum oxide has been studied in situ by timeresolved 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 gamma-to-alpha transformation velocity and, over the limited range studied, do so in proportion to their concentration. Concentrations of Er as low as similar to6 ppm retard the gamma-to-alpha 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 alpha-phase transformation. Erbium also retards the amorphous-to-gamma transformation relative to undoped alumina whereas yttrium and chromium accelerate it.