Native defect-induced multifarious magnetism in nonstoichiometric cuprous oxide: First-principles study of bulk and surface properties of Cu 2-δO

Aloysius Soon, Xiang Yuan Cui, Bernard Delley, Su Huai Wei, Catherine Stampfl

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Abstract

Native defects in cuprous oxide Cu2O are investigated by using first-principles calculations based on density-functional theory. Considering the formation of copper and oxygen vacancies, antisites and interstitials, and a copper split-vacancy complex defect, we analyze the electronic structure and calculate their respective formation energies as a function of the change in Fermi level under both copper-rich and oxygen-rich conditions. We find that, under both growth conditions, the defect with the lowest formation energy is the simple copper vacancy, followed by the copper split-vacancy complex. Both low-energy copper defects produce hole states at the top of the valence band, largely accounting for the p -type conductivity in this material. In spite of the creation of dangling bonds at the nearest-neighbor O atoms, these copper defects are found to be spin neutral. Under oxygen-rich conditions, oxygen interstitials have low formation energies and are found to exhibit a ferromagnetic ordering with a total magnetic moment of 1.38 μB and 1.36 μB at the octahedral and tetrahedral sites, respectively. Considering the possibility of native defect formation at the surface of this material, we investigate the relative stability of both low- and high-index copper-oxide surfaces by comparing their surface free energies as a function of the change in oxygen chemical potential. Using the technique of ab initio atomistic thermodynamics, we then correlate the dependence of the calculated Gibbs free-surface energy as a function of oxygen pressure and temperature via the oxygen chemical potential. We identify two low-energy surface structures, namely, Cu2O (110): CuO and Cu2O (111) -CuCUS, with the former marginally more stable for oxygen-rich conditions and the latter more stable for oxygen-lean (or copper-rich) conditions. Cu2O (110): CuO is calculated to be nonmagnetic and Cu2O (111) -CuCUS is calculated to be a ferromagnetic ordering, with a total magnetic moment of 0.91 μB per defect. With the results for both bulk and surface native defects, we find that under oxygen-lean conditions, a ferromagnetic behavior could be attributed mainly to copper vacancy formation in the (111) surface of Cu2O while under oxygen-rich conditions, low-energy bulk oxygen interstitial defects induce a ferromagnetic character in the same material. This highlights the complementary role of bulk and surface native magnetic defects under different pressure and temperature conditions, especially at the nanoparticle scale where surface properties dominate.

Original languageEnglish
Article number035205
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume79
Issue number3
DOIs
Publication statusPublished - 2009 Jan 5

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Magnetism
surface properties
Surface properties
Copper
Oxygen
Defects
Oxides
oxides
defects
oxygen
copper
Vacancies
energy of formation
Chemical potential
interstitials
Magnetic moments
surface energy
cuprous oxide
magnetic moments
Dangling bonds

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics

Cite this

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title = "Native defect-induced multifarious magnetism in nonstoichiometric cuprous oxide: First-principles study of bulk and surface properties of Cu 2-δO",
abstract = "Native defects in cuprous oxide Cu2O are investigated by using first-principles calculations based on density-functional theory. Considering the formation of copper and oxygen vacancies, antisites and interstitials, and a copper split-vacancy complex defect, we analyze the electronic structure and calculate their respective formation energies as a function of the change in Fermi level under both copper-rich and oxygen-rich conditions. We find that, under both growth conditions, the defect with the lowest formation energy is the simple copper vacancy, followed by the copper split-vacancy complex. Both low-energy copper defects produce hole states at the top of the valence band, largely accounting for the p -type conductivity in this material. In spite of the creation of dangling bonds at the nearest-neighbor O atoms, these copper defects are found to be spin neutral. Under oxygen-rich conditions, oxygen interstitials have low formation energies and are found to exhibit a ferromagnetic ordering with a total magnetic moment of 1.38 μB and 1.36 μB at the octahedral and tetrahedral sites, respectively. Considering the possibility of native defect formation at the surface of this material, we investigate the relative stability of both low- and high-index copper-oxide surfaces by comparing their surface free energies as a function of the change in oxygen chemical potential. Using the technique of ab initio atomistic thermodynamics, we then correlate the dependence of the calculated Gibbs free-surface energy as a function of oxygen pressure and temperature via the oxygen chemical potential. We identify two low-energy surface structures, namely, Cu2O (110): CuO and Cu2O (111) -CuCUS, with the former marginally more stable for oxygen-rich conditions and the latter more stable for oxygen-lean (or copper-rich) conditions. Cu2O (110): CuO is calculated to be nonmagnetic and Cu2O (111) -CuCUS is calculated to be a ferromagnetic ordering, with a total magnetic moment of 0.91 μB per defect. With the results for both bulk and surface native defects, we find that under oxygen-lean conditions, a ferromagnetic behavior could be attributed mainly to copper vacancy formation in the (111) surface of Cu2O while under oxygen-rich conditions, low-energy bulk oxygen interstitial defects induce a ferromagnetic character in the same material. This highlights the complementary role of bulk and surface native magnetic defects under different pressure and temperature conditions, especially at the nanoparticle scale where surface properties dominate.",
author = "Aloysius Soon and Cui, {Xiang Yuan} and Bernard Delley and Wei, {Su Huai} and Catherine Stampfl",
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Native defect-induced multifarious magnetism in nonstoichiometric cuprous oxide : First-principles study of bulk and surface properties of Cu 2-δO. / Soon, Aloysius; Cui, Xiang Yuan; Delley, Bernard; Wei, Su Huai; Stampfl, Catherine.

In: Physical Review B - Condensed Matter and Materials Physics, Vol. 79, No. 3, 035205, 05.01.2009.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Native defect-induced multifarious magnetism in nonstoichiometric cuprous oxide

T2 - First-principles study of bulk and surface properties of Cu 2-δO

AU - Soon, Aloysius

AU - Cui, Xiang Yuan

AU - Delley, Bernard

AU - Wei, Su Huai

AU - Stampfl, Catherine

PY - 2009/1/5

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N2 - Native defects in cuprous oxide Cu2O are investigated by using first-principles calculations based on density-functional theory. Considering the formation of copper and oxygen vacancies, antisites and interstitials, and a copper split-vacancy complex defect, we analyze the electronic structure and calculate their respective formation energies as a function of the change in Fermi level under both copper-rich and oxygen-rich conditions. We find that, under both growth conditions, the defect with the lowest formation energy is the simple copper vacancy, followed by the copper split-vacancy complex. Both low-energy copper defects produce hole states at the top of the valence band, largely accounting for the p -type conductivity in this material. In spite of the creation of dangling bonds at the nearest-neighbor O atoms, these copper defects are found to be spin neutral. Under oxygen-rich conditions, oxygen interstitials have low formation energies and are found to exhibit a ferromagnetic ordering with a total magnetic moment of 1.38 μB and 1.36 μB at the octahedral and tetrahedral sites, respectively. Considering the possibility of native defect formation at the surface of this material, we investigate the relative stability of both low- and high-index copper-oxide surfaces by comparing their surface free energies as a function of the change in oxygen chemical potential. Using the technique of ab initio atomistic thermodynamics, we then correlate the dependence of the calculated Gibbs free-surface energy as a function of oxygen pressure and temperature via the oxygen chemical potential. We identify two low-energy surface structures, namely, Cu2O (110): CuO and Cu2O (111) -CuCUS, with the former marginally more stable for oxygen-rich conditions and the latter more stable for oxygen-lean (or copper-rich) conditions. Cu2O (110): CuO is calculated to be nonmagnetic and Cu2O (111) -CuCUS is calculated to be a ferromagnetic ordering, with a total magnetic moment of 0.91 μB per defect. With the results for both bulk and surface native defects, we find that under oxygen-lean conditions, a ferromagnetic behavior could be attributed mainly to copper vacancy formation in the (111) surface of Cu2O while under oxygen-rich conditions, low-energy bulk oxygen interstitial defects induce a ferromagnetic character in the same material. This highlights the complementary role of bulk and surface native magnetic defects under different pressure and temperature conditions, especially at the nanoparticle scale where surface properties dominate.

AB - Native defects in cuprous oxide Cu2O are investigated by using first-principles calculations based on density-functional theory. Considering the formation of copper and oxygen vacancies, antisites and interstitials, and a copper split-vacancy complex defect, we analyze the electronic structure and calculate their respective formation energies as a function of the change in Fermi level under both copper-rich and oxygen-rich conditions. We find that, under both growth conditions, the defect with the lowest formation energy is the simple copper vacancy, followed by the copper split-vacancy complex. Both low-energy copper defects produce hole states at the top of the valence band, largely accounting for the p -type conductivity in this material. In spite of the creation of dangling bonds at the nearest-neighbor O atoms, these copper defects are found to be spin neutral. Under oxygen-rich conditions, oxygen interstitials have low formation energies and are found to exhibit a ferromagnetic ordering with a total magnetic moment of 1.38 μB and 1.36 μB at the octahedral and tetrahedral sites, respectively. Considering the possibility of native defect formation at the surface of this material, we investigate the relative stability of both low- and high-index copper-oxide surfaces by comparing their surface free energies as a function of the change in oxygen chemical potential. Using the technique of ab initio atomistic thermodynamics, we then correlate the dependence of the calculated Gibbs free-surface energy as a function of oxygen pressure and temperature via the oxygen chemical potential. We identify two low-energy surface structures, namely, Cu2O (110): CuO and Cu2O (111) -CuCUS, with the former marginally more stable for oxygen-rich conditions and the latter more stable for oxygen-lean (or copper-rich) conditions. Cu2O (110): CuO is calculated to be nonmagnetic and Cu2O (111) -CuCUS is calculated to be a ferromagnetic ordering, with a total magnetic moment of 0.91 μB per defect. With the results for both bulk and surface native defects, we find that under oxygen-lean conditions, a ferromagnetic behavior could be attributed mainly to copper vacancy formation in the (111) surface of Cu2O while under oxygen-rich conditions, low-energy bulk oxygen interstitial defects induce a ferromagnetic character in the same material. This highlights the complementary role of bulk and surface native magnetic defects under different pressure and temperature conditions, especially at the nanoparticle scale where surface properties dominate.

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