Atomistic and ab initio DFT modelling of the defect structures in Al3+/Cr3+-doped and co-doped Y3Fe5O12

Hisham Widatallah, Muataz S. Al-Barwani, Elaine A. Moore, Mohamed Elzain

Research output: Contribution to journalArticle

2 Citations (Scopus)

Abstract

The defect structures when Y3Fe5O12 is doped with either Al3+ or Cr3+, and evenly co-doped with both, which have been a matter of controversy in the literature, are modeled using atomistic and ab initio DFT methods. When Y3Fe5O12 is doped with Al3+, the defect reaction energy obtained marginally favors the preferential substitution of Al3+ for Fe3+ at the tetrahedral sites as opposed to octahedral ones. This is indicative that for Al3+-doped samples processed at elevated temperatures, or containing undetected impurities, the substitution of Al3+ for octahedral Fe3+ is likely. To model the defect structure of the Cr3+ -doped Y3Fe5O12, it was essential that the Cr3+ ions crystal field stabilization energy (CFSE) and the Fe3+-O2-- Cr3+ spin-spin coupling derived from the ab initio DFT calculations,be taken into account. The results show the substitution of the Cr3+ ion for an octahedral Fe3+ ion to be energetically favorable relative to its substitution for a tetrahedral Fe3+ one. It is also shown that the antisite defect, where the Cr3+ ion substitutes for Y3+ at a dodecahedral site with the expelled Y3+ ion substituting for an octahedral Fe3+ ion, is possible under certain processing conditions. For the Al3+ /Cr3+ co-doped Y3Fe5O12, the Al3+ and Cr3+ ions were found to, respectively, substitute for the tetrahedral and octahedral Fe3+ ions. The energy values obtained suggest this defect structure to be insensitive to the processing conditions and/or the presence of undetected impurities. The structural and magnetic implications of these defect structures are discussed.

Original languageEnglish
Pages (from-to)100-106
Number of pages7
JournalJournal of Physics and Chemistry of Solids
Volume119
DOIs
Publication statusPublished - Aug 1 2018

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Defect structures
Discrete Fourier transforms
Ions
defects
substitutes
ions
Substitution reactions
Impurities
antisite defects
impurities
Defects
spin-spin coupling
Processing
crystal field theory
energy
Stabilization
stabilization
Crystals

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics

Cite this

Atomistic and ab initio DFT modelling of the defect structures in Al3+/Cr3+-doped and co-doped Y3Fe5O12 . / Widatallah, Hisham; Al-Barwani, Muataz S.; Moore, Elaine A.; Elzain, Mohamed.

In: Journal of Physics and Chemistry of Solids, Vol. 119, 01.08.2018, p. 100-106.

Research output: Contribution to journalArticle

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abstract = "The defect structures when Y3Fe5O12 is doped with either Al3+ or Cr3+, and evenly co-doped with both, which have been a matter of controversy in the literature, are modeled using atomistic and ab initio DFT methods. When Y3Fe5O12 is doped with Al3+, the defect reaction energy obtained marginally favors the preferential substitution of Al3+ for Fe3+ at the tetrahedral sites as opposed to octahedral ones. This is indicative that for Al3+-doped samples processed at elevated temperatures, or containing undetected impurities, the substitution of Al3+ for octahedral Fe3+ is likely. To model the defect structure of the Cr3+ -doped Y3Fe5O12, it was essential that the Cr3+ ions crystal field stabilization energy (CFSE) and the Fe3+-O2-- Cr3+ spin-spin coupling derived from the ab initio DFT calculations,be taken into account. The results show the substitution of the Cr3+ ion for an octahedral Fe3+ ion to be energetically favorable relative to its substitution for a tetrahedral Fe3+ one. It is also shown that the antisite defect, where the Cr3+ ion substitutes for Y3+ at a dodecahedral site with the expelled Y3+ ion substituting for an octahedral Fe3+ ion, is possible under certain processing conditions. For the Al3+ /Cr3+ co-doped Y3Fe5O12, the Al3+ and Cr3+ ions were found to, respectively, substitute for the tetrahedral and octahedral Fe3+ ions. The energy values obtained suggest this defect structure to be insensitive to the processing conditions and/or the presence of undetected impurities. The structural and magnetic implications of these defect structures are discussed.",
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AB - The defect structures when Y3Fe5O12 is doped with either Al3+ or Cr3+, and evenly co-doped with both, which have been a matter of controversy in the literature, are modeled using atomistic and ab initio DFT methods. When Y3Fe5O12 is doped with Al3+, the defect reaction energy obtained marginally favors the preferential substitution of Al3+ for Fe3+ at the tetrahedral sites as opposed to octahedral ones. This is indicative that for Al3+-doped samples processed at elevated temperatures, or containing undetected impurities, the substitution of Al3+ for octahedral Fe3+ is likely. To model the defect structure of the Cr3+ -doped Y3Fe5O12, it was essential that the Cr3+ ions crystal field stabilization energy (CFSE) and the Fe3+-O2-- Cr3+ spin-spin coupling derived from the ab initio DFT calculations,be taken into account. The results show the substitution of the Cr3+ ion for an octahedral Fe3+ ion to be energetically favorable relative to its substitution for a tetrahedral Fe3+ one. It is also shown that the antisite defect, where the Cr3+ ion substitutes for Y3+ at a dodecahedral site with the expelled Y3+ ion substituting for an octahedral Fe3+ ion, is possible under certain processing conditions. For the Al3+ /Cr3+ co-doped Y3Fe5O12, the Al3+ and Cr3+ ions were found to, respectively, substitute for the tetrahedral and octahedral Fe3+ ions. The energy values obtained suggest this defect structure to be insensitive to the processing conditions and/or the presence of undetected impurities. The structural and magnetic implications of these defect structures are discussed.

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