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Energetics of Aluminum Vacancies and Incorporation of Foreign Trivalent Ions in γ‐Al 2 O 3 : An Atomistic Simulation Study
Author(s) -
Maglia Filippo,
Gennari Silvia,
Buscaglia Vincenzo
Publication year - 2008
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1551-2916.2007.02149.x
Subject(s) - octahedron , ion , spinel , interatomic potential , crystallography , density functional theory , materials science , tetrahedron , chemistry , molecular dynamics , computational chemistry , crystal structure , metallurgy , organic chemistry
Atomistic simulation methods based on pair‐wise interatomic potentials and energy minimization have been applied to elucidate the energetics of cation vacancies and the incorporation of 13 trivalent M 3+ cations (Cr 3+ , Ga 3+ , Fe 3+ , Lu 3+ , Yb 3+ , Er 3+ , Y 3+ , Tb 3+ , Gd 3+ , Eu 3+ , Sm 3+ , Nd 3+ , La 3+ ) in γ‐Al 2 O 3 . Calculations have been carried out using Al 64 O 96 defect spinel supercells containing eight aluminum vacancies. The lowest energy configurations correspond to a random distribution of tetrahedral and octahedral vacancies. The energy gain in comparison with exclusive tetrahedral or octahedral vacancies is rather small (0.03 and 0.09 eV/Al 2 O 3 , respectively). Unit cell volume, density, and lattice properties of optimized structures are in good agreement with the experimental values or the results of high‐quality density functional theory calculations. The trends observed for the solution energy of the M 2 O 3 oxides in the supercell with minimum energy indicate the preferential incorporation of the foreign ions at the tetrahedral site and an increase of the solubility of M 2 O 3 in the defect spinel in comparison with α‐Al 2 O 3 . Configurations with the lowest energy have negative solution energies and, consequently, incorporation of trivalent ions can improve the thermodynamic stability of γ‐Al 2 O 3 in comparison with α‐Al 2 O 3 and increase the γ→α transition temperature.