Rare‐Earth Dopant Effects on the Structural, Energetic, and Magnetic Properties of Alumina from First Principles

Abstract

Density functional theory was used to study the effect of rare‐earth dopants on the structure, phase stability, and magnetic properties of α‐ and θ‐Al2O3. Lanthanide series rare‐earth dopants (Pr, Nd, Gd, Er, and Yb) were considered at a doping concentration of 0.83 at.%. Incorporation of rare‐earth dopants was found to increase the lattice parameters and exaggerate the local structural distortion around the dopant. The extent of local lattice distortion was correlated with the dopant ionic radii. The phase stability of rare‐earth‐doped Al2O3 was assessed by comparing cohesive and defect formation energies for doped and undoped α‐ and θ‐Al2O3. Rare‐earth dopants increased the relative stability of the metastable θ‐Al2O3, although doped α‐Al2O3 remained more stable. The total magnetic moment of the doped Al2O3 was shown to correlate with the number of unpaired electrons. The magnetic moment was also found to be strongly localized on the rare‐earth dopant for Er, Gd, Nd, and Pr‐doped Al2O3. In contrast, the Yb dopant induced a delocalized magnetic moment on ~80% of the oxygen atoms. These results further the understanding of dopant incorporation mechanisms, as well as the doping effect on phase stability and magnetic properties that may be applied to advanced field‐assisted material synthesis and processing for enhanced properties.

Magnetic and energetic properties of transition metal doped alumina

“…are in good agreement with other GGA calculations and only slightly overestimate the experimental values (see supplemental information for full comparison available online at stacks.iop.org/JPhysCM/30/395801/mmedia). For αalumina, the lattice vectors reported in this work are iden tical to the lattice vectors reported in [13] and within 1% of previous work, yielding a volume within 3%. Similarly, the lattice vectors reported for ϑalumina are within 1.4% of the literature, again yielding a volume within 3%.…”

“…In addition, work by Anderson et al, which included some transition metals, concluded that doping did not significantly affect the physical properties of alumina, thereby preserving its wear resistance, and ability to be used for armor applica tions [12]. Previous research examining rare earth doped alumina concluded that lanthanide doping may significantly affect the processing of alumina in the presence of a magnetic field [13]. A similar effect is expected from the 3d transition metals.…”

Towards magnetic alumina: uncovering the roles of transition metal doping and electron hybridization in spin delocalization

“…Our previous work selected these supercell dimensions to minimize interaction of the dopant with its periodic image, simulating a dilute substitutional solid solution. Larger cells change the defect formation energy by less than 0.3 meV [9,19].…”

“…Past research suggests that the total magnetic moment in the super cell may only be a partial descriptor of magnetic activity and that it is possible for dopants which are not typically considered to be good candidates for inducing magnetism to induce non-localized spin densities that are superior for texturing purposes [8,19]. It is important, therefore, to characterize not just the total magnetic moment, but also how widely distributed the magnetic moment is.…”

Effect of Water Vapor on Alumina Scale Growth Based on First-Principles Calculations

“…The energetic favorable configuration of the vacancies is obtained by comparing the system energies with the vacancy at different lattice sites of the supercell. The perfect θ-Al 2 O 3 (the same structure as that of β-Ga 2 O 3 ) unit cell has a monoclinic structure with 20 atoms, , where O atoms can be considered approximately in the hexagonal closed stacking planes and Al atoms occupy octahedral and tetrahedral interstitial sites (as shown in Figure c). Relatively large supercells with low defect concentrations are adopted to preclude any appreciable interactions between the point defect and the supercell boundaries.…”