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Structural and electronic properties of Eu- and Pd-doped ZnO.

Assadi MH, Zhang Y, Zheng RK, Ringer SP, Li S - Nanoscale Res Lett (2011)

Bottom Line: The ground state properties, equilibrium bond lengths, and band structures of both the ZnO:Eu and ZnO:Pd systems were also investigated.The total and partial densities of electron states were also determined for both systems.It was found that in the ZnO:Eu system, ambient ferromagnetism can be induced by introducing Zn interstitial which leads to a carrier-mediated ferromagnetism while the ZnO:Pd system possesses no ferromagnetism.PACS 31.15.E-, 75.50.Pp, 75.30Hx.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Materials Science and Engineering, The University of New South Wales, Sydney, NSW 2052, Australia. sean.li@unsw.edu.au.

ABSTRACT
Doping ZnO with rare earth and 4d transition elements is a popular technique to manipulate the optical properties of ZnO systems. These systems may also possess intrinsic ferromagnetism due to their magnetic moment borne on 4f and 4d electrons. In this work, the structural, electronic, and magnetic properties of Eu- and Pd-doped ZnO were investigated by the ab initio density functional theory methods based on generalized gradient approximation. The relative stability of incorporation sites of the doped elements in the ZnO host lattice was studied. The ground state properties, equilibrium bond lengths, and band structures of both the ZnO:Eu and ZnO:Pd systems were also investigated. The total and partial densities of electron states were also determined for both systems. It was found that in the ZnO:Eu system, ambient ferromagnetism can be induced by introducing Zn interstitial which leads to a carrier-mediated ferromagnetism while the ZnO:Pd system possesses no ferromagnetism.PACS 31.15.E-, 75.50.Pp, 75.30Hx.

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Total and partial density of states of the ZnO:Pd systems. Representing (a) ZnO:PdZn, (b) the ZnO:PdI, (c) ZnO:PdZn + VO, (d) ZnO:PdZn + ZnI systems. The solid black lines and the blue-shaded areas represent the total and Pd's partial 4d states, respectively. For clarity, the Pd's d states are scaled by a factor of five. Also, energy is represented with respect to the Fermi level.
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Figure 4: Total and partial density of states of the ZnO:Pd systems. Representing (a) ZnO:PdZn, (b) the ZnO:PdI, (c) ZnO:PdZn + VO, (d) ZnO:PdZn + ZnI systems. The solid black lines and the blue-shaded areas represent the total and Pd's partial 4d states, respectively. For clarity, the Pd's d states are scaled by a factor of five. Also, energy is represented with respect to the Fermi level.

Mentions: To investigate the electronic properties of the ZnO:Pd systems, the total and partial density of states of both systems were calculated and presented in Figure 4. As in Figure 4a, the 4d states of PdZn and O's 2p states hybridize and form bonding (tb) states in the valence band. The antibonding 4d states with e symmetry are located above the tb states, separated by a gap of approximately 1 eV from the valance band maximum and positioned just below the Fermi Level. The position of the PdZn antibonding states with respect to the Fermi level indicates an n-type behavior of the ZnO:PdZn. Notably, the 4d states are completely degenerate for spin-up and spin-down states with no exchange splitting. This implies that PdZn does not induce any magnetization. For PdI, according to Figure 4b, the 4d states of PdI are split into bonding and antibonding states. The bonding states with the tb symmetry hybridize with O's 2p orbitals along the valance band. The antibonding states with e symmetry are divided into three peaks in the fundamental bandgap region. This is the major difference of the DOS of the PdI and PdZn, which may be caused by the different crystal fields experienced by each site. The closely located peaks in the bandgap region results in the high optical activity of the ZnO:PdI system, in particular, they may be the mechanism behind the observed red shift in the photoluminescence spectrum in the ZnO:Pd system [13]. The position of the e states from the Fermi level and the absence of exchange splitting indicate that PdI is an n-type dopant with no magnetization. In nonstochiometric systems, ZnO:PdZn + VO and ZnO:PdZn + ZnI, the Pd's 4d states, as shown in Figure 4c, d, are distributed in a similar pattern to the ZnO:PdZn. It exhibits the Pd's spin-up and spin-down states which are fully degenerate, indicating the absence of any magnetization per Pd ion. Therefore, these systems are nonmagnetic even when VO and ZnI exist in the ZnO:Pd system.


Structural and electronic properties of Eu- and Pd-doped ZnO.

Assadi MH, Zhang Y, Zheng RK, Ringer SP, Li S - Nanoscale Res Lett (2011)

Total and partial density of states of the ZnO:Pd systems. Representing (a) ZnO:PdZn, (b) the ZnO:PdI, (c) ZnO:PdZn + VO, (d) ZnO:PdZn + ZnI systems. The solid black lines and the blue-shaded areas represent the total and Pd's partial 4d states, respectively. For clarity, the Pd's d states are scaled by a factor of five. Also, energy is represented with respect to the Fermi level.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211447&req=5

Figure 4: Total and partial density of states of the ZnO:Pd systems. Representing (a) ZnO:PdZn, (b) the ZnO:PdI, (c) ZnO:PdZn + VO, (d) ZnO:PdZn + ZnI systems. The solid black lines and the blue-shaded areas represent the total and Pd's partial 4d states, respectively. For clarity, the Pd's d states are scaled by a factor of five. Also, energy is represented with respect to the Fermi level.
Mentions: To investigate the electronic properties of the ZnO:Pd systems, the total and partial density of states of both systems were calculated and presented in Figure 4. As in Figure 4a, the 4d states of PdZn and O's 2p states hybridize and form bonding (tb) states in the valence band. The antibonding 4d states with e symmetry are located above the tb states, separated by a gap of approximately 1 eV from the valance band maximum and positioned just below the Fermi Level. The position of the PdZn antibonding states with respect to the Fermi level indicates an n-type behavior of the ZnO:PdZn. Notably, the 4d states are completely degenerate for spin-up and spin-down states with no exchange splitting. This implies that PdZn does not induce any magnetization. For PdI, according to Figure 4b, the 4d states of PdI are split into bonding and antibonding states. The bonding states with the tb symmetry hybridize with O's 2p orbitals along the valance band. The antibonding states with e symmetry are divided into three peaks in the fundamental bandgap region. This is the major difference of the DOS of the PdI and PdZn, which may be caused by the different crystal fields experienced by each site. The closely located peaks in the bandgap region results in the high optical activity of the ZnO:PdI system, in particular, they may be the mechanism behind the observed red shift in the photoluminescence spectrum in the ZnO:Pd system [13]. The position of the e states from the Fermi level and the absence of exchange splitting indicate that PdI is an n-type dopant with no magnetization. In nonstochiometric systems, ZnO:PdZn + VO and ZnO:PdZn + ZnI, the Pd's 4d states, as shown in Figure 4c, d, are distributed in a similar pattern to the ZnO:PdZn. It exhibits the Pd's spin-up and spin-down states which are fully degenerate, indicating the absence of any magnetization per Pd ion. Therefore, these systems are nonmagnetic even when VO and ZnI exist in the ZnO:Pd system.

Bottom Line: The ground state properties, equilibrium bond lengths, and band structures of both the ZnO:Eu and ZnO:Pd systems were also investigated.The total and partial densities of electron states were also determined for both systems.It was found that in the ZnO:Eu system, ambient ferromagnetism can be induced by introducing Zn interstitial which leads to a carrier-mediated ferromagnetism while the ZnO:Pd system possesses no ferromagnetism.PACS 31.15.E-, 75.50.Pp, 75.30Hx.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Materials Science and Engineering, The University of New South Wales, Sydney, NSW 2052, Australia. sean.li@unsw.edu.au.

ABSTRACT
Doping ZnO with rare earth and 4d transition elements is a popular technique to manipulate the optical properties of ZnO systems. These systems may also possess intrinsic ferromagnetism due to their magnetic moment borne on 4f and 4d electrons. In this work, the structural, electronic, and magnetic properties of Eu- and Pd-doped ZnO were investigated by the ab initio density functional theory methods based on generalized gradient approximation. The relative stability of incorporation sites of the doped elements in the ZnO host lattice was studied. The ground state properties, equilibrium bond lengths, and band structures of both the ZnO:Eu and ZnO:Pd systems were also investigated. The total and partial densities of electron states were also determined for both systems. It was found that in the ZnO:Eu system, ambient ferromagnetism can be induced by introducing Zn interstitial which leads to a carrier-mediated ferromagnetism while the ZnO:Pd system possesses no ferromagnetism.PACS 31.15.E-, 75.50.Pp, 75.30Hx.

No MeSH data available.


Related in: MedlinePlus