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

Abstract

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.

Ab initiocalculations on the effects of additives on alumina phase stability

“…Such studies have mainly been focused on increasing the thermal stability of the metastable aluminas and report results on the transformation kinetics. To summarize these results it can be said that many dopants seem to retard the ␥ to ␣ transformation (e.g., Cr, [10][11][12] Cs, 13 B, 14 La, 4,15 Ce, 4,15 Ba, 16 Sr, 16 Ca, 16 Er, 11 Y 11 ), while some accelerate the transformation (e.g., Fe, 10,17 Cu 17 ), effects which have been partly explained by kinetic arguments. However, the direct influence of the dopants on structural stability has not yet been elucidated.…”

Anodization behaviour and basic property mapping in the aluminium-erbium system

“…Er is also an interesting alloying element for tuning properties of oxides: glass formation and polyamorphism have already been reported [12][13][14][15]. While the influence of Al on ZnO for further improvement of transparent conductive oxides is well studied, addition of Er has been demonstrated to allow tuning of ZnO electrical properties [16].…”

Energetics of Aluminum Vacancies and Incorporation of Foreign Trivalent Ions in γ‐Al2O3: An Atomistic Simulation Study

“…when the crystal size is smaller than ≈10 nm 4 . Nanocrystalline γ‐Al 2 O 3 can be obtained by dehydration and thermal decomposition of γ‐AlOH (boehmite) at 300°–500°C or by crystallization of amorphous alumina thin films produced by anodic oxidation of aluminum in acid solution 1 or by vapor deposition 5 . On further heating, the sequence of transformations γ→δ→θ→α is generally observed.…”