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Journal ArticleDOI

Influence of transition metal doping on the structural, optical, and magnetic properties of TiO2 films deposited on Si substrates by a sol-gel process.

19 Dec 2013-Nanoscale Research Letters (Springer)-Vol. 8, Iss: 1, pp 533-533

TL;DR: It is found that the magnetizations of the TM-doped TiO2 films decrease with increasing dopant content, which is related to electric disorder due to the ART.

AbstractTransition metal (TM)-doped TiO2 films (TM = Co, Ni, and Fe) were deposited on Si(100) substrates by a sol–gel method. With the same dopant content, Co dopants catalyze the anatase-to-rutile transformation (ART) more obviously than Ni and Fe doping. This is attributed to the different strain energy induced by the different dopants. The optical properties of TM-doped TiO2 films were studied with spectroscopic ellipsometry data. With increasing dopant content, the optical band gap (EOBG) shifts to lower energy. With the same dopant content, the EOBG of Co-doped TiO2 film is the smallest and that of Fe-doped TiO2 film is the largest. The results are related to electric disorder due to the ART. Ferromagnetic behaviors were clearly observed for TM-doped TiO2 films except the undoped TiO2 film which is weakly magnetic. Additionally, it is found that the magnetizations of the TM-doped TiO2 films decrease with increasing dopant content.

Topics: Dopant (59%), Doping (53%), Band gap (52%)

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Citations
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Journal ArticleDOI
TL;DR: Among the samples, Fe-1wt% doped TiO2 nanoparticles showed the highest photocatalytic decolorization of RR198 under visible light irradiation.
Abstract: In this research, Fe-doped TiO2 nanoparticles with various Fe concentrations (0. 0.1, 1, 5 and 10wt%) were prepared by a sol-gel method. Then, nanoparticles were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray analysis (EDX), BET surface area, photoluminescence (PL) spectroscopy and UV-vis diffuse reflectance spectroscopy (DRS). The photocatalytic activity of the nano-particles was evaluated through degradation of reactive red 198 (RR 198) under UV and visible light irradiations. XRD results revealed that all samples contained only anatase phase. DRS showed that the Fe doping in the titania induced a significant red shift of the absorption edge and then the band gap energy decreased from 3 to 2.1eV. Photocatalytic results indicated that TiO2 had a highest photocatalytic decolorization of the RR 198 under UV irradiation whereas photocatalytic decolorization of the RR 198 under visible irradiation increased in the presence of Fe-doped TiO2 nanoparticles. Among the samples, Fe-1wt% doped TiO2 nanoparticles showed the highest photocatalytic decolorization of RR198 under visible light irradiation.

98 citations


Journal ArticleDOI
Abstract: Our paper reports structural, magnetic and ferroelectric properties of Ni doped barium titanate. Ceramics samples of BaTi 1− x Ni x O 3 (here, x =0, 0.05, 0.1, and 0.15) were prepared through solid state sintering technique. It is revealed from structural studies that the phase transformation from tetragonal to hexagonal phase is strongly influenced by Ni doping concentration. Magnetism is induced in doped composition and the value of magnetism is dependent upon Ni ion concentration. This enhanced magnetic effect is likely to originate from carrier-mediated exchange interactions. Ferroelectricity was observed in all samples at room temperature, but it was decreased by Ni doping.

71 citations


Journal ArticleDOI
Abstract: In this paper, the Fe-Ni co-doped and Ag deposited anatase TiO2 (Fe-Ni/Ag/TiO2) nanocomposites were successfully prepared by a simple one-pot solvothermal approach. The investigations indicated that all as-prepared TiO2 samples were single anatase phase, and the impurity level was generated due to the Fe3+ or Ni2+ being located in the intrinsic band gap of TiO2, while the Ag+ ions could be transformed into metallic silver due to the reduction reaction and then loaded onto the surface of TiO2. Compared with pure TiO2, Fe-Ni/Ag/TiO2 composites with the sizes of Ag nanoparticles from 1.0 to 3.0 nm displayed the well optical property including higher visible light absorption activity and lower electron-hole pair recombination rate, and its absorption wavelength edge moved remarkably with a red shift to 700 nm. The photocatalytic water splitting was performed to produce H2 over the samples, and the experimental results indicate that Fe-Ni/Ag/TiO2 composites presented the highest H2 evolution rate, it can reach up to 793.86 μmol h−1 gcat−1 (λ > 400 nm for 6 h, energy efficiency is 0.25%), which was much higher than that of pure TiO2 for 9.57 μmol h−1 gcat−1. In addition, a tentative photocatalytic mechanism is proposed to understand the enhancement mechanism over Fe-Ni codoped and Ag deposited anatase TiO2.

44 citations


Journal ArticleDOI
Abstract: We report undoped and Ni-doped TiO 2 ( x Ni = 0.00, 0.50, 1.00, 1.50, 2.00 and 2.50 wt.%) thin films fabricated on glass substrates by using a combination of solid-state reaction and dip coating techniques. The structural properties are observed by X-ray diffraction (XRD), which have depicted that annealing at 650 °C results in rutile Ni-doped TiO 2 as a major phase along with a minor anatase phase. The surface morphology of the deposited thin films, as measured by scanning electron microscopy (SEM), indicates granular spherical shaped nanostructures. Room-temperature ferromagnetism (RTFM) has been illustrated by all the grown thin films, as elucidated by vibrating sample magnetometer (VSM). Although Ni content has no pronounced effect on the crystallinity that indicates a substitutional replacement of Ni in TiO 2 lattice, however, Ni content is observed to influence the ferromagnetic behavior. Therefore, the present study signifies the potential spintronic applications of Ni-doped TiO 2 diluted magnetic semiconductors, fabricated by a low-cost method, as it exhibits RTFM with nanograins at the surface.

43 citations


Journal ArticleDOI
11 Jan 2018
TL;DR: The enhanced rate capability and cycling stability were attributed to the enlargement of the NaO2 slab in the crystal structure because of Ti doping, which promoted Na-ion diffusion and prevented the phase transition from the P2 to the OP4/″Z″ structure.
Abstract: In this study, we developed a doping technology capable of improving the electrochemical performance, including the rate capability and cycling stability, of P2-type Na0.67Fe0.5Mn0.5O2 as a cathode material for sodium-ion batteries. Our approach involved using titanium as a doping element to partly substitute either Fe or Mn in Na0.67Fe0.5Mn0.5O2. The Ti-substituted Na0.67Fe0.5Mn0.5O2 shows superior electrochemical properties compared to the pristine sample. We investigated the changes in the crystal structure, surface chemistry, and particle morphology caused by Ti doping and correlated these changes to the improved performance. The enhanced rate capability and cycling stability were attributed to the enlargement of the NaO2 slab in the crystal structure because of Ti doping. This promoted Na-ion diffusion and prevented the phase transition from the P2 to the OP4/″Z″ structure.

36 citations


References
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11 Feb 2000-Science
TL;DR: Zener's model of ferromagnetism, originally proposed for transition metals in 1950, can explain T(C) of Ga(1-)(x)Mn(x)As and that of its II-VI counterpart Zn(1)-Mn (x)Te and is used to predict materials with T (C) exceeding room temperature, an important step toward semiconductor electronics that use both charge and spin.
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"Influence of transition metal dopin..." refers methods in this paper

  • ...Some theory models, such as the Ruderman-Kittel-Kasuya-Yosida exchange [4], super exchange [5], double exchange [6], magnetic polarons [7], and F-center exchange mechanism [8], have been used to explain ferromagnetism in transitionmetal-element-doped TiO2....

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Journal ArticleDOI
TL;DR: It is proposed thatferromagnetic exchange here, and in dilute ferromagnetic nitrides, is mediated by shallow donor electrons that form bound magnetic polarons, which overlap to create a spin-split impurity band.
Abstract: Dilute ferromagnetic oxides having Curie temperatures far in excess of 300 K and exceptionally large ordered moments per transition-metal cation challenge our understanding of magnetism in solids. These materials are high-k dielectrics with degenerate or thermally activated n-type semiconductivity. Conventional super-exchange or double-exchange interactions cannot produce long-range magnetic order at concentrations of magnetic cations of a few percent. We propose that ferromagnetic exchange here, and in dilute ferromagnetic nitrides, is mediated by shallow donor electrons that form bound magnetic polarons, which overlap to create a spin-split impurity band. The Curie temperature in the mean-field approximation varies as (xdelta)(1/2) where x and delta are the concentrations of magnetic cations and donors, respectively. High Curie temperatures arise only when empty minority-spin or majority-spin d states lie at the Fermi level in the impurity band. The magnetic phase diagram includes regions of semiconducting and metallic ferromagnetism, cluster paramagnetism, spin glass and canted antiferromagnetism.

2,590 citations


Journal ArticleDOI
S. H. Wemple1, M. DiDomenico1
Abstract: Refractive-index dispersion data below the interband absorption edge in more than 100 widely different solids and liquids are analyzed using a single-effective-oscillator fit of the form ${n}^{2}\ensuremath{-}1=\frac{{E}_{d}{E}_{0}}{({E}_{0}^{2}\ensuremath{-}{\ensuremath{\hbar}}^{2}{\ensuremath{\omega}}^{2})}$, where $\ensuremath{\hbar}\ensuremath{\omega}$ is the photon energy, ${E}_{0}$ is the single oscillator energy, and ${E}_{d}$ is the dispersion energy. The parameter ${E}_{d}$, which is a measure of the strength of interband optical transitions, is found to obey the simple empirical relationship ${E}_{d}=\ensuremath{\beta}{N}_{c}{Z}_{a}{N}_{e}$, where ${N}_{c}$ is the coordination number of the cation nearest neighbor to the anion, ${Z}_{a}$ is the formal chemical valency of the anion, ${N}_{e}$ is the effective number of valence electrons per anion (usually ${N}_{e}=8$), and $\ensuremath{\beta}$ is essentially two-valued, taking on the "ionic" value ${\ensuremath{\beta}}_{i}=0.26\ifmmode\pm\else\textpm\fi{}0.04$ eV for halides and most oxides, and the "covalent" value ${\ensuremath{\beta}}_{c}=0.37\ifmmode\pm\else\textpm\fi{}0.05$ eV for the tetrahedrally bonded ${A}^{N}{B}^{8\ensuremath{-}N}$ zinc-blende- and diamond-type structures, as well as for scheelite-structure oxides and some iodates and carbonates. Wurtzite-structure crystals form a transitional group between ionic and covalent crystal classes. Experimentally, it is also found that ${E}_{d}$ does not depend significantly on either the bandgap or the volume density of valence electrons. The experimental results are related to the fundamental ${\ensuremath{\epsilon}}_{2}$ spectrum via appropriately defined moment integrals. It is found, using relationships between moment integrals, that for a particularly simple choice of a model ${\ensuremath{\epsilon}}_{2}$ spectrum, viz., constant optical-frequency conductivity with high- and low-frequency cutoffs, the bandgap parameter ${E}_{a}$ in the high-frequency sum rule introduced by Hopfield provides the connection between the single-oscillator parameters (${E}_{0},{E}_{d}$) and the Phillips static-dielectric-constant parameters (${E}_{g},\ensuremath{\hbar}{\ensuremath{\omega}}_{p}$), i.e., ${(\ensuremath{\hbar}{\ensuremath{\omega}}_{p})}^{2}={E}_{a}{E}_{d} \mathrm{and} {E}_{g}^{2}={E}_{a}{E}_{0}$. Finally, it is suggested that the observed dependence of ${E}_{d}$ on coordination number and valency implies that an understanding of refractive-index behavior may lie in a localized molecular theory of optical transitions.

2,040 citations


"Influence of transition metal dopin..." refers background in this paper

  • ...Note that it is common to observe the development of an Urbach tail on doping transition metal oxides [45,46]....

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Journal ArticleDOI
Abstract: Zener has suggested a type of interaction between the spins of magnetic ions which he named "double exchange." This occurs indirectly by means of spin coupling to mobile electrons which travel from one ion to the next. We have calculated this interaction for a pair of ions with general spin $S$ and with general transfer integral, $b$, and internal exchange integral $J$.One result is that while the states of large total spin have both the highest and lowest energies, their average energy is the same as for the states of low total spin. This should be applicable in the high-temperature expansion of the susceptibility, and if it is, indicates that the high-temperature Curie-Weiss constant $\ensuremath{\theta}$ should be zero, and $\frac{1}{\ensuremath{\chi}}$ vs $T$ a curved line. This is surprising in view of the fact that the manganites, in which double exchange has been presumed to be the interaction mechanism, obey a fairly good Curie-Weiss law.The results can be approximated rather well by a simple semiclassical model in which the spins of the ion cores are treated classically. This model is capable of rather easy extension to the problem of the whole crystal, but the resulting mathematical problem is not easily solved except in special circumstances, e.g., periodic disturbances (spin waves).

2,000 citations


"Influence of transition metal dopin..." refers methods in this paper

  • ...Some theory models, such as the Ruderman-Kittel-Kasuya-Yosida exchange [4], super exchange [5], double exchange [6], magnetic polarons [7], and F-center exchange mechanism [8], have been used to explain ferromagnetism in transitionmetal-element-doped TiO2....

    [...]