Theoretical Structure Determination of a Complex Material: κ‐Al₂O₃

Abstract

The atomic and electronic structures of kappa‐Al2O3 are determined using theoretical first‐principles techniques based on density‐functional theory (DFT), plane waves, and pseudopotentials. The obtained structure is confirmed by analysis of powder X‐ray diffraction data. The structure is orthorhombic with oxygen ions in close‐packed ABAC stacking and aluminum ions occupying both tetrahedral (1/4) and octahedral (3/4) interstitial sites. A growth model for chemical vapor deposition of kappa‐Al2O3 is proposed based on the atomic structure. Calculated electronic structure and charge density yield a band gap of 5.3 eV and a high ionic character of the bonds. The study shows the applicability of DFT‐based methods to complex and metastable materials.

Thermal stability of doped CVD κ-Al2O3 coatings

“…This is in good agreement with the preferred growth orientation of CVD κ-Al 2 O 3 layers reported in literature [43,44]. The residual tensile stresses are increasing from ∼ 240 MPa to ∼290 MPa and ∼390 MPa, for undoped, B-doped and Ti-B-doped κ-Al 2 O 3 bilayers, respectively.…”

Influence of micro-blasting on the microstructure and residual stresses of CVD κ-Al2O3 coatings

“…This observation may be supported by previous investigations indicating a higher degree of plasticity of α-Al 2 O 3 [37] compared to κ-Al 2 O 3 . On the other hand, the different physical characteristics of the metastable CVD κ-Al 2 O 3 compared to the CVD α-Al 2 O 3 , such as a smaller grain size, a lower pore density and an epitaxial growth, may also have an influence on the internal stress conditions after micro-blasting treatment [35].…”

“…It has an orthorhombic crystal structure (space group Pna2 1 ) with lattice parameters a = 4.844 Å, b = 8.330 Å, c = 8.955 Å formed from a pseudo-closed-packed stacking ABAC of oxygen atoms with Al in octahedral and tetrahedral environments in a 3:1 ratio [35,36]. Supposedly, due to the rather complex crystalline structure, distortion of the lattice occurs differently according to the crystallographic direction leading to twinning as the predominant deformation mechanism in κ-Al 2 O 3 phase in contrast to α-Al 2 O 3 , in which dislocation is the type of recurrent defects observed.…”

Predicted structure and stability ofA4B3O12δ-phase compositions

“…The 45 configurations were determined by a lattice algebra technique, which was originally used to determine the structure of -Al 2 O 3 . 25 For the ordered structure of Y 4 Zr 3 O 12 , Bogicevic et al 23 predicted the 3a sites to be exclusively occupied by Zr 4+ and the 18f sites occupied by Y 3+ and Zr 4+ in an ordered arrangement. This result was confirmed in a recent theoretical study by Predrith, et al 26 …”