Yttrium, an Isoelectric Donor in α ‐ Al ₂ O ₃

Measurements of dc electrical conductivity and emf of single crystal and polycrystalline α‐Al 2 O 3 doped, respectively, with 100 and 300 ppm yttrium show that yttrium, although isoelectronic with aluminum, is a donor. The electronic energy level of the donor is attributed to O 2‐ next to Y 3+ , its level being forced up as a result of the large size of the yttrium ion. The donor activity of Y supports the view that the favorable effect of Y on the oxidation of super alloys is due to reduced diffusion of Al in the bulk through a reduced concentration of Al i … without a marked increase in the concentration of V … Al .