3d Transition Metal Impurities Research Articles

Effect of 3d transition metal impurities doping on electronic and magnetic properties of CeO2

The effect of transition metal (TM) impurities, namely Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn, on the electronic and magnetic properties of Ceria dioxide is studied using the Korringa-Kohn-Rostoker method combined with the coherent potential approximation (KKR-CPA). Calculations indicate that pure CeO2 is a nonmagnetic indirect semiconductor. Doping this compound with transition metals results in three main groups based on their electromagnetic behavior. The first group involves CeO2 doped with Sc, Ti and Zn which show a lack of magnetism at low concentrations. The second group of TMs, including V, Mn, Fe and Ni, induces half-metallic character and ferromagnetic behavior. Finally, when Cr, Co and Cu are substituted in CeO2, this doping creates magnetic semiconductors with a direct band gap. The origin of the magnetic states is further discussed and the Curie temperatures are determined. The present work shows that controlling impurity type and concentration renders Cerium dioxide a potential candidate for spintronic applications.

Effects of 3d transition metal impurities and vacancy defects on electronic and magnetic properties of pentagonal Pd2S4: competition between exchange splitting and crystal fields

In this paper, we first investigate the electronic properties of the two-dimensional structure of dichalcogenide Pd2S4. These properties strongly depend on the crystal field splitting which can change by atomic vacancies (S and Pd vacancies). The main purpose of the present paper is to create remarkable magnetic properties in the system by adding 3d transition metal atoms where the presence of Mn, Cr, and Fe creates the exchange interaction in the system as well as change in the crystal field. The created magnetic properties strongly depend on the competition between exchange interaction and crystal field to separate the levels of d orbitals. In addition, the presence of the transition metals in the structures with S and Pd vacancy has been investigated carefully. The calculations demonstrate that we can achieve an extensive range of magnetic moment up to 3.131 {mu }_{B}. The maximum one is obtained in the presence of Mn and absence of sulfur while some of the doped structures does not have magnetic moment. Our results show that Pd vacancy in the presence of Cr, Mn and Fe metals increases the magnetic property of the Pd2S4 structure. The extensiveness and variety of the obtained properties can be used for different magnetic and non-magnetic applications.

Magnetic properties of Pb-=SUB=-1-y-=/SUB=-Sc-=SUB=-y-=/SUB=-Te alloys

The magnetic field dependences of the magnetization (B≤9 T, T=2-70 K) of the samples from a single crystal Pb1-yScyTe (y=0.01) ingot, synthesized by the Bridgman method, are studied. It is established that, in accordance with the generally accepted model of the rearrangement of the electronic structure of alloys during doping, there is no paramagnetic contribution of single scandium ions located in the nodes of the metal sublattice in the studied samples. The magnetization of the samples contains several contributions: superparamagnetism of scandium clusters, linear in field diamagnetism of the crystal lattice and the paramagnetism of free electrons, as well as the oscillating contribution of the de Haas--van Alphen effect. The field dependences of the main contribution of scandium clusters are successfully approximated using the Langevin function. The average concentration, magnetic moment and the total magnetic moment of the clusters per unit volume of the sample were determined with an increase in the impurity concentration along the ingot. Keywords: PbTe-based alloys, 3d-transition metal impurities, rearrangement of electronic structure, field dependences of magnetization, superparamagnetism of scandium clusters.

Structural, Electronic, and Magnetic Properties of 3d Transition Metal–Doped BP Nanotubes by First Principle Calculations

The structural, electronic, and magnetic properties of 3d transition metal (TM) (TM = V, Cr, Mn, Fe, Co, Ni, and Cu)–doped boron phosphide nanotubes (BPNTs) in armchair (5, 5) form were performed using first principle calculations. The 3d TMs were replaced by B atomic position. It was found that there is a distortion around 3d TM impurities, with respect to the pristine BPNTs. All the doped structures, except Cu-doped BPNT, showed the magnetic behavior. Fe-, Co-, and Ni-doped are ferromagnetic metal whereas Cu-doped is nonmagnetic gapless. Moreover, the Cr- and Mn-doped behaved as magnetic semiconductors whereas Mn-doped BPNT has maximum magnetic moment. Furthermore, doping V in BPNT lead to the magnetic gapless or zero-gap semi-metal. The obtained property is useful for industrial applications, especially in spintronic devices.

Influence of 3d Transition Metal Impurities on Garnet Scintillator Afterglow

Garnet scintillators often suffer from undesired afterglow, the origin of which is not always well-understood. A possible origin is contamination with transition metal (TM) ions. These impurities can act as traps giving rise to afterglow. Alternatively, they may show long-lived (microsecond) d–d emission. Here we present a systematic study on the role of 3d TM impurities in (Lu,Gd)3(Ga,Al)5O12 garnet scintillators. Scintillator disks intentionally doped with ppm levels of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, or Zn were studied to identify TM-related traps in thermoluminescence (TSL) glow curves and their role in afterglow. For Ti, V, and Cr additional TSL peaks were observed that gave rise to RT afterglow in the 10–2–103 s time range, depending on garnet composition. On the millisecond time scale long-lived red/near-infrared emission was observed from Mn and Fe impurities, explained by spin-forbidden d–d emission. We show that afterglow can be reduced by the use of ultrapure raw materials. Other solutions include bandgap engineering for the garnet host to modify trap depths and applying optical filters to block the spin-forbidden d–d emission. The present study provides an insightful overview of the role of 3d TM impurities on afterglow in Ce-doped scintillators and procedures to predict and reduce afterglow. These insights will aid the development of Ce-doped garnets with superior afterglow behavior.

Chemical origin of differences in steel corrosion behaviors of s-electron and p-electron liquid metals by first-principles calculation.

Steel corrosion is a key engineering issue in the development of advanced nuclear reactors using liquid metals. The present study demonstrates that the steel corrosion behaviors can be systematically understood and classified based on the types of valence electrons of liquid metals, namely, s-electron liquid metals (s-LMs), such as liquid Na and Li, and p-electron liquid metals (p-LMs), such as liquid lead-bismuth eutectic (LBE) and Pb, where the conduction band is composed of s and p valence electrons, respectively. Through a comparative analysis of the physiochemical states of 3d transition metal atoms dissolved in liquid Na and liquid LBE by means of first-principles molecular dynamics (FPMD), it is shown that the 3d and 4s orbitals of the transition metals hardly interact with the s band of s-LMs, while they strongly interact with the p band of p-LMs in a covalent manner. This fact is consistently seen in the electronic states and the atomic configuration and can be successfully used to explain the differences in the steel corrosion behaviors observed between the liquid metals by experiments. The present findings provide fundamental insights into the corrosion chemistry of liquid metals.

Composition dependent tuning of electronic and magnetic properties in transition metal substituted Rock-salt MgO

Abstract Full potential linearized augmented plane wave (FP-LAPW) method based on the density functional theory (DFT) is used to investigate the structural, electronic and magnetic properties of Fe and Ni (3d transition metal) substituted Rock-salt wide band gap insulator M g 1 - x M x O (M = Fe, Ni). We have performed spin polarized calculations throughout this work with generalized gradient approximation (GGA) type exchange correlation functional. Additionally, the electronic structures and density of states are computed using modified Becke-Johnson (mBJ) potential based approximation with the inclusion of coulomb energy (U = 7 eV). Based on the Vegard’s law and structural optimization, the lattice parameter and bulk modulus are found to be in good agreement with experimental values. Moreover, the analysis of electronic band structures reveals an insulating character for Ni substituted MgO while semiconducting and half-metallic character for Fe substituted case. It has been found that the p-d super-exchange interaction provides a ferromagnetic character due to the 3d transition metal impurities and oxygen atom. The observed p-d hybridization at the top of the valence band edge in this investigations could be useful for magneto-optic and spintronic applications. PACS: 61.66.Dk; 71.15.Mb; 71.15.Nc; 71.20.Nr; 71.22.+ i.

Chemical states of 3d transition metal impurities in a liquid lead-bismuth eutectic analyzed using first principles calculations.

Steels are easily corroded in a liquid lead-bismuth eutectic (LBE) because their components, such as Fe, Cr and Ni, exhibit a high solubility in the liquid LBE. To understand the reason for such a high solubility of these 3d transition metals, we have performed first-principles molecular dynamics calculations and analyzed the pair-correlation functions, electronic densities of states, and Bader charges and volumes of the 3d transition metals dissolved in the liquid LBE as impurities. The calculations show that the 4s and 3d orbitals of the 3d impurity atoms largely interact with the 6p band of the LBE, which generates bonding orbitals. We suggest that the high stability of 3d metals in the liquid LBE is caused by the interactions of the 4s and 3d orbitals with the 6p band. Spin polarization is induced by V, Cr, Mn, Fe and Co impurity atoms in a similar manner to the Slater-Pauling curve of solid transition metals, which exhibits a downward shift in the atomic number by approximately two. Based on the degree of spin polarization and the shifted trend of the Slater-Pauling curve, we suggest that Ni exhibits a higher solubility than Cr and Fe because of the differences in their interaction strengths between their 3d orbitals and the 6p band. In addition, the 4s and 3d orbitals of the 3d impurity atoms were found to interact more favorably with the Bi 6p band than the Pb 6p band, which is consistent with the fact that liquid Bi is more corrosive to steels than is liquid Pb.

Solvent-Based Atomistic Theory for Doping Colloidal-Synthesized Quantum Dots via Cation Exchange

Electronic applications require the ability to dope a material with a controllable amount of impurities. However, current understanding of the doping mechanism in colloidal–synthesized quantum dots (QDs) is still limited. This is in contrast with bulk semiconductors for which first-principles-based theories have been well established. Using prototype CdSe as an example, here we propose an atomistic theory for the doping of colloidal-synthesized QDs. The key in our theory is the evaluation of atomic chemical potential inside the solution, whose range can deviate considerably from the bulk value due to the presence of solvent. This theory, coupled to first-principles calculations and ab initio molecular dynamics, is able to explain the difference of doping limit in Mn (or Co)-doped CdSe QDs and their bulk counterparts. It also explains the doping behavior of a number of other 3d transition-metal impurities in CdSe QDs in contrast with the solid case.

Effect of transition metal impurities on the strength of grain boundaries in vanadium

Effects of 3d (Ti-Ni), 4d (Zr-Pd), and 5d (Hf-Pt) transition metal impurities on strength of two representative vanadium grain boundaries (GBs), symmetric Σ3(111) and asymmetric Σ5(210), were studied by first-principles calculations within the framework of the Rice-Wang thermodynamic model and within the computational tensile test. The desirable elements to increase the GB cohesion were predicted based on their segregation and strengthening behaviors across the different GB sites. It reveals that the elements Ti, Zr, Hf, Nb, and Ta are good choices for the GB cohesion enhancers. In addition, the GB strengthening by solutes is sensitive to the GB structures. The elements Cr, Mn, Fe, Co, and Ni decrease the GB strength of the Σ3(111) GB but they can increase the cohesion of the Σ5(210) GB. Furthermore, the origin of Ti-induced change of the GB strength was uncovered by analyzing the atomic bonds and electronic structures as well as the tensile strength. This work provides a theoretical guidance to screen promising alloying elements in V-based materials with improved resistance to GB decohesion and also helps us to understand the formation mechanism of Ti-rich precipitates in the V-Cr-Ti alloys under neutron or ion irradiation environments.

Dilute Magnetic Semiconductor and Half-Metal Behaviors in 3d Transition-Metal Doped Black and Blue Phosphorenes: A First-Principles Study.

We present first-principles density-functional calculations for the structural, electronic, and magnetic properties of substitutional 3d transition metal (TM) impurities in two-dimensional black and blue phosphorenes. We find that the magnetic properties of such substitutional impurities can be understood in terms of a simple model based on the Hund’s rule. The TM-doped black phosphorenes with Ti, V, Cr, Mn, Fe, and Ni impurities show dilute magnetic semiconductor (DMS) properties while those with Sc and Co impurities show nonmagnetic properties. On the other hand, the TM-doped blue phosphorenes with V, Cr, Mn, and Fe impurities show DMS properties, with Ni impurity showing half-metal properties, whereas Sc- and Co-doped systems show nonmagnetic properties. We identify two different regimes depending on the occupation of the hybridized electronic states of TM and phosphorous atoms: (i) bonding states are completely empty or filled for Sc- and Co-doped black and blue phosphorenes, leading to nonmagnetic; (ii) non-bonding d states are partially occupied for Ti-, V-, Cr-, Mn-, Fe- and Ni-doped black and blue phosphorenes, giving rise to large and localized spin moments. These results provide a new route for the potential applications of dilute magnetic semiconductor and half-metal in spintronic devices by employing black and blue phosphorenes.PACS numbers: 73.22.-f, 75.50.Pp, 75.75. + a

Zn17Superatom Cage Doped with 3d Transition-Metal (TM) Impurities (TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu)

A systematic theoretical study of the doping of Zn17 nanoparticle with 3d transition-metal (TM) impurities is presented. Calculations are conducted within the density functional framework as implemented in the VASP code at the generalized gradient approximation for the exchange and correlation effects. The ground state of Zn17 has been recently shown to be a dihedral superatom hollow cage in a singlet state [Angew. Chem., Int. Ed. 2015, 54, 2111]. We show that, among the 3d elements, endohedral doping of a quasi-undeformed cage results favorable only for Cr and Cu, which as free atoms display a very stable (half-filled and fully occupied, respectively) d shell electron configuration. This structural configuration allows to maximize the spin magnetic moment of the chromium-doped cage. Co and Ni also adopt an endohedral configuration, but with a strong deformation of the cage and a rather compact structure due to the large electron hybridization between the TM states and those of the Zn host. Doping with th...

Tailoring Electronic and Magnetic Properties of MoS2 Nanotubes

We have studied the electronic and magnetic structures of MoS2 nanotubes by using a first-principles method. Various kinds of defects such as substitution and vacancy are examined for triggering spin magnetic moments toward one-dimensional diluted magnetic semiconductors. Our results suggest that the presence of impurity states within the energy gap and its large contribution to the density of states at the Fermi level are the key factors in inducing a magnetic moment. In particular, the nanotube curvature turns out to affect the energy level of impurity states, which can be exploited for tailoring magnetic properties. Also, 3d transition metal impurities (V, Mn, Fe, and Co atoms) on a Mo site can create large magnetic moments.

Interstitial impurity-induced magnetism in α-PbO surface

We have investigated the effects of 3d transition metal (TM) and non-magnetic interstitial impurities in α-PbO (0 0 1) surface using ab-initio calculations. The calculated impurity-induced magnetic moments are 2.25 μB, 3.11 μB and 0.94 μB for Fe, Mn and Pb interstitials respectively. In the bonding process, TM's lower energy lying states form overlaps with nearest neighbour oxygen atoms' pz states, with other non-bonding spin split d states situated near or at the Fermi level. These spin split orbitals introduce spin polarised p impurity states of oxygen atoms near the surface.

Systematic study of electronic and magnetic properties for Cu12–xTMxSb4S13 (TM = Mn, Fe, Co, Ni, and Zn) tetrahedrite

Substitution effects of 3d transition metal (TM) impurities on electronic and magnetic properties for Cu12Sb4S13 tetrahedrite are investigated by the combination of low-temperature experiments and first-principles electronic-structure calculations. The electrical resistivity for the cubic phase of Cu12Sb4S13 exhibits metallic behavior due to an electron-deficient character of the compound. Whereas that for 0.5 ≤ x ≤ 2.0 of Cu12−xNixSb4S13 exhibits semiconducting behavior. The substituted Ni for Cu is in the divalent ionic state with a spin magnetic moment and creates impurity bands just above the Fermi level at the top of the valence band. Therefore, the semiconducting behavior of the electrical resistivity is attributed to the thermal excitation of electrons from the valence band to the impurity band. The substitution effect of TM on the electronic structure and the valency of TM for Cu11.0TM1.0Sb4S13 are systematically studied by the calculation. The substituted Mn, Fe, and Co for Cu are found to be in the ionic states with the spin magnetic moments due to the large exchange splitting of the 3d bands between the minority- and majority-spin states.

Direct d–d interactions among transition metal impurities in III–V semiconductors

We investigate the direct d–d interactions among substitutional 3d transition metal impurities in various III–V semiconductor hosts by first-principles calculations. We find that for nearest neighbor impurity pairs, such d–d interactions, to some extent, always appear. These d–d interactions become particularly important for light 3d transition metal impurities in nitride semiconductors, which may lead to dramatic effects in the magnetic and chemical interactions.

Effects of the 3d transition metal doping on the structural, electronic, and magnetic properties of BeO nanotubes

First-principles calculations have been performed on the structural, electronic, and magnetic properties of seven 3d transition-metal (TM) impurities (V, Cr, Mn, Fe, Co, Ni, and Cu) doped armchair (5,5) and zigzag (8,0) beryllium oxide nanotubes (BeONTs). The results show that there exists a structural distortion around the 3d TM impurities with respect to the pristine BeONTs. The magnetic moment increases for V- and Cr-doped BeONTs and reaches a maximum for Mn-doped BeONT, and then decreases for Fe-, Co-, Ni-, and Cu-doped BeONTs successively, consistent with the predicted trend of Hund's rule to maximize the magnetic moments of the doped TM ions. However, the values of the magnetic moments are smaller than the predicted values of Hund's rule due to the strong hybridization between the 2p orbitals of the near O and Be ions of BeONTs and the 3d orbitals of the TM ions. Furthermore, the V-, Co-, and Ni-doped (5,5) and (8,0) BeONTs with half-metal ferromagnetism and thus 100% spin polarization character are good candidates for spintronic applications.

Structural stability and electronic properties of small gold clusters induced by 3p electron atoms

The geometries and electronic properties of gold clusters doped with atoms containing 3p valence electrons (MAun; M = Al, Si, P, S, Cl; n = 2−8) have been systematically investigated using density functional theory (DFT) at the PBE/LANL2DZ level. A number of low-energy isomers are identified for neutral MAun clusters. It is found that doping with different 3p impurity atoms can drastically influence the geometrical structures, relative stabilities, electronic properties, and growth-pattern behaviors of gold clusters, which is very different from the case of 3d transition-metal impurity doped Aun clusters. Partially filled 3p electron impurities can stabilize Au clusters. In particular, SiAu4 cluster with Td symmetry have been found to have highly stable geometries and electronic structures with binding energies of 2.43 eV per atom (0.96 eV higher than pristine Au5 clusters), large HOMO-LUMO gaps (2.17 eV), and vertical ionization potentials of 8.68 eV. Using scalar relativistic molecular dynamics at T = 300 K, we show that the Td symmetry structure of SiAu4 is stable. The frontier molecular orbitals (HOMO and LUMO) and the partial densities of states (PDOS) show that strong hybridization occurs between the atomic orbitals of Si and Au atoms, resulting in strong Si-Au bonding. In addition, the vertical ionization potential, the vertical electron affinity, and charge transfers of MAun clusters have also been analyzed. Our results are in good agreement with available experimental data.

Electronic properties of iron and cobalt impurity centres in germanium

The electronic properties of the 3d transition metal impurities iron and cobalt in crystalline germanium have been investigated by means of deep level transient spectroscopy. The metals were implanted at 90 keV and diffused deeper into the bulk during a thermal anneal at 500 °C, which yielded spectra specific for the implanted metal. It was found that Fe introduces one deep electron trap and one deep hole trap. For Co, one deep electron trap and two hole traps were observed. The capture cross-section of both electron and hole traps has been directly measured. The results are in agreement with the metals being present on substitutional lattice sites forming multiple acceptor states. It is concluded that Fe and Co are double acceptors in germanium, with Co having an additional donor level close to the valence band.

3dtransition metal impurities in diamond: Electronic properties and chemical trends

First principles calculations have been used to investigate the trends on the properties of isolated 3d transition metal impurities (from Sc to Cu) in diamond. Those impurities have small formation energies in the substitutional or double semi-vacancy sites, and large energies in the interstitial one. Going from Sc to Cu, the 3d-related energy levels in the bandgap move from the top of the bandgap toward the valence band in all three sites. Trends in electronic properties and transition energies of the impurities, in the substitutional or interstitial sites, are well described by a simple microscopic model considering the electronic occupation of the 3d-related levels. On the other hand, for the impurities in the double semi-vacancy site, there is a weak interaction between the divacancy- and the 3d-related orbitals, resulting in in vacancy- and 3d-related levels in the materials bandgap.