Physical Properties and Structure of rf-Sputtered Amorphous Films in the System Al2O3–Y2O3

Amorphous films in the system Al₂O₃–Y₂O₃ were prepared by the rf sputtering method in the range of 0–76 mol% Y₂O₃, and their density, refractive index, and elastic constants were measured. All of the physical properties of the amorphous Al₂O₃–Y₂O₃ films had a similar compositional dependence; that is, they increased continuously, but not linearly with increasing Y₂O₃ content. To confirm the coordination states of aluminum and yttrium ions in the amorphous Al₂O₃–Y₂O₃ films, the Al K α X-ray emission spectra and the X-ray absorption near edge structures (XANES) were measured. The average coordination number of aluminum ions in the amorphous films containing up to about 40 mol% Y₂O₃ content was 5, that is a mixture of 4-fold- and 6-fold-coordinated states. In the region of more than about 50 mol% Y₂O₃, the fraction of the 6-fold-coordinated aluminum ions increased with increasing Y₂O₃ content, while the results led to the conclusion that the coordination number of yttrium ions was always 6, regardless of composition. These results indicate that, in amorphous films in the system Al₂O₃–Y₂O₃, the change of the coordination state of aluminum ions has an important effect on physical properties.