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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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The relaxed crystallographic structure of the ZnO:Pd systems. Representing (a) ZnO:PdZn, (b) ZnO:PdI, (c) ZnO:PdZn + VO, (d) ZnO:PdZn + ZnI systems. Red, blue, and gray balls represent the O, Zn, and Pd ions, respectively. For each system, the calculated length of the Eu bonds is presented along both the c direction (or [001]) and within the ab (basal) plane.
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Figure 3: The relaxed crystallographic structure of the ZnO:Pd systems. Representing (a) ZnO:PdZn, (b) ZnO:PdI, (c) ZnO:PdZn + VO, (d) ZnO:PdZn + ZnI systems. Red, blue, and gray balls represent the O, Zn, and Pd ions, respectively. For each system, the calculated length of the Eu bonds is presented along both the c direction (or [001]) and within the ab (basal) plane.

Mentions: In the ideal ZnO lattice, the length of the O-Zn bond within the basal plane is 1.997 Å. The radius of O-2 being 1.40 Å, leaves enough room for Pd+2 with an atomic radius of 0.64 Å to substitute the Zn+2 ion without significant lattice distortion to create a PdZn. Alternatively, Pd+2 can fit in the octahedral interstitial site which is located in the interstitial channel along c axis. In addition to the octahedral interstitial site, there is a tetrahedral interstitial site in ZnO which has a Zn+2 ion and an O-2 ion as nearest-neighbor atoms, at a distance of about 1.67 Å, (0.833 times the Zn-O bond length along the c axis). Thus, a Pd ion cannot be placed at this site without severe geometric constraints. In order to determine the preferred site of the Pd ion in the ZnO lattice, the Ef of Pd for both the ZnO:PdI and ZnO:PdZn systems were calculated. It was found that the Ef of PdZn and PdI were 0.776 and 1.612 eV. Such a difference results in high concentration of PdZn over the PdI in thermal equilibrium condition in the ZnO:Pd system. Such a finding is in agreement with the reported experimental data that Pd+2 tends to substitute Zn+2 in ZnO [13]. Figure 3a, b show the local geometry of PdZn and PdI in ZnO. For the ZnO:PdZn system, the Pd-O is 2.127 and 2.199 Å along c direction and within the ab plane, respectively with approximate expansions of 6% and 10%, respectively compared to the unrelaxed structure. For the ZnO:PdI system, the Pd-O and Pd-Zn bonds have increased to 2.236 and 2.451 Å, respectively with the expansions of 11% and 6% with respect to the unrelaxed structure. Similar to the ZnO:Eu system, in the ZnO:Pd system, PdZn has a lower Ef and causes less lattice distortion. Electronically, a Mullikan population analysis indicated that both PdZn and PdI are isovalent to the Zn ions, transferring two electrons to neighboring O ions. This implies that Pd's 4d shell remains fully occupied, thus the Pd ions are not magnetized in the ZnO host lattice which is reflected in zero magnetization of Pd ions in all configurations as presented in Table 2. As a result, the stochiometric ZnO:Pd system is nonmagnetic.


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

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

The relaxed crystallographic structure of the ZnO:Pd systems. Representing (a) ZnO:PdZn, (b) ZnO:PdI, (c) ZnO:PdZn + VO, (d) ZnO:PdZn + ZnI systems. Red, blue, and gray balls represent the O, Zn, and Pd ions, respectively. For each system, the calculated length of the Eu bonds is presented along both the c direction (or [001]) and within the ab (basal) plane.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 3: The relaxed crystallographic structure of the ZnO:Pd systems. Representing (a) ZnO:PdZn, (b) ZnO:PdI, (c) ZnO:PdZn + VO, (d) ZnO:PdZn + ZnI systems. Red, blue, and gray balls represent the O, Zn, and Pd ions, respectively. For each system, the calculated length of the Eu bonds is presented along both the c direction (or [001]) and within the ab (basal) plane.
Mentions: In the ideal ZnO lattice, the length of the O-Zn bond within the basal plane is 1.997 Å. The radius of O-2 being 1.40 Å, leaves enough room for Pd+2 with an atomic radius of 0.64 Å to substitute the Zn+2 ion without significant lattice distortion to create a PdZn. Alternatively, Pd+2 can fit in the octahedral interstitial site which is located in the interstitial channel along c axis. In addition to the octahedral interstitial site, there is a tetrahedral interstitial site in ZnO which has a Zn+2 ion and an O-2 ion as nearest-neighbor atoms, at a distance of about 1.67 Å, (0.833 times the Zn-O bond length along the c axis). Thus, a Pd ion cannot be placed at this site without severe geometric constraints. In order to determine the preferred site of the Pd ion in the ZnO lattice, the Ef of Pd for both the ZnO:PdI and ZnO:PdZn systems were calculated. It was found that the Ef of PdZn and PdI were 0.776 and 1.612 eV. Such a difference results in high concentration of PdZn over the PdI in thermal equilibrium condition in the ZnO:Pd system. Such a finding is in agreement with the reported experimental data that Pd+2 tends to substitute Zn+2 in ZnO [13]. Figure 3a, b show the local geometry of PdZn and PdI in ZnO. For the ZnO:PdZn system, the Pd-O is 2.127 and 2.199 Å along c direction and within the ab plane, respectively with approximate expansions of 6% and 10%, respectively compared to the unrelaxed structure. For the ZnO:PdI system, the Pd-O and Pd-Zn bonds have increased to 2.236 and 2.451 Å, respectively with the expansions of 11% and 6% with respect to the unrelaxed structure. Similar to the ZnO:Eu system, in the ZnO:Pd system, PdZn has a lower Ef and causes less lattice distortion. Electronically, a Mullikan population analysis indicated that both PdZn and PdI are isovalent to the Zn ions, transferring two electrons to neighboring O ions. This implies that Pd's 4d shell remains fully occupied, thus the Pd ions are not magnetized in the ZnO host lattice which is reflected in zero magnetization of Pd ions in all configurations as presented in Table 2. As a result, the stochiometric ZnO:Pd system is nonmagnetic.

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