Yttrium, an Isoelectric Donor in α ‐ Al₂O₃

Abstract

Measurements of dc electrical conductivity and emf of single crystal and polycrystalline α‐Al2O3 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 O2‐ next to Y3+, 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 Ali… without a marked increase in the concentration of V…Al.

The Characteristics of Alumina Scales Formed on Fe‐Based Yttria‐Dispersed Alloys

“…[22] is made up of contributions from the temperature dependence of 8 and the temperature dependence of Do *gb. The present results for 8Do *Sb may be compared with values for 8Do ~b calculated from Oishi and Kingery (20) 8I)o gb = 1.4 x 10 -3 exp (-llO,O00/RT) [24] and values measured by Reddy (31) 8/:)0 gb = 6.15 exp (-142,000/RT) [25] However, no oxygen partial pressure dependencies are available for these values.…”

Susceptibility of minor alloying to corrosion behavior in yttrium-containing bulk amorphous steel

“…When yttrium is present in the alloy, the ionized yttrium atoms could incorporate into the passive film by substituting Fe 3þ cations as donors (Y 3þ can be doped as isoelectric donor Y Fe 3þ [26]) [23,27]. Thus, it is expected that owing to its large size, yttrium cation induces a localized point defect complex, correspondingly, resulting in the generation of excessive oxygen vacancies.…”

Oxidation of an Fe-Cr-Al-Y-Zr alloy forming an alumina scale in a Ga2O atmosphere at 1473 K

“…Wang and Kröger [44] suggested as the mobile species in the chemical diffusion of alumina doped with Fe and Ti. For alumina doped with yttrium, El-Aiat and Kröger [45] interpreted their conductivity measurements that yttrium forms a donor defect, giving a relatively positive charge because of yttrium's large ionic radius when substituted in an aluminum site . On the basis of Kröger's analysis [46] concerning the effects of Ti, Y, and Zr dopants on diffusion and conductivity of Al 2 O 3 , would form at the oxide/gas interface according to the following reaction: [12] The oxygen transforms into a neutral oxygen interstitial, , diffusing through the alumina scale and reacting with Al as follows:…”

“…Although the oxygen partial pressure was not varied within the ampoule and was established by the Ga (1)/Ga 2 O 3 coexistence, as explained previously, the inference by the Kroger group [44,45,46] of an allows the authors of the present study to deduce a model of its generation at the gas/scale interface and its consumption at the scale/metal interface.…”