Defect energetics and nonstoichiometry in lanthanum magnesium hexaaluminate

Journal Article · Thu May 01 04:00:00 EDT 1997 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1006/jssc.1996.7141· OSTI ID:577470

Park, J G; Cormack, A N ^[1]

---

1. Alfred Univ., NY (United States)

Computer-based atomistic simulation methods are applied to address quantitatively the defect energetics and crystal chemistry of lanthanum magnesium hexaaluminate (LMA). The tetrahedral site preference of Mg in the magnetoplumbite structure is determined by calculating lattice energies for different Mg ion distributions. It is revealed that the intrinsic and extrinsic disorders are much influenced by the distribution of Mg in the structure. Our calculations show that oxygen Frenkel disorder is the dominant defect mode to be expected, even though Schottky disorder may also exist. Several feasible defect processes in nonstoichiometric LMA are determined from the enthalpies of the quasi-chemical reactions for the processes with simple point defect energies. We have also modeled some defect complexes in the mirror plane regions. It is found that the Mg ions positioned in the tetrahedral sites suppress the formation of cation vacancies in the mirror plane, through hindering the relaxation of the 12k Al ions by which the vacancies are stabilized. In Mg-deficient nonstoichiometric LMA, however, it is expected that the defect complex [V{sub La} + V{sub Al} + 2 (V{sub Al} + Al{sub I})] will be formed in the interspinel layer. Our calculations also indicate that the O{sub La} defect is improbable in LMA not only as a simple point defect but also as a member of a defect complex.

• DOE Contract Number: FG02-91ER45451
• OSTI ID: 577470
• Journal Information: Journal of Solid State Chemistry, Journal Name: Journal of Solid State Chemistry Journal Issue: 2 Vol. 130; ISSN 0022-4596; ISSN JSSCBI
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM OXIDES
CRYSTAL DEFECTS
LANTHANUM OXIDES
MAGNESIUM OXIDES
RELAXATION
VACANCIES