Room-temperature ferromagnetism in Ni-doped TiO2 diluted magnetic semiconductor thin films
TL;DR: In this paper, undoped and Ni-doped TiO 2 ( x Ni ǫ = 0.00, 0.50, 1.00 and 2.50 ) thin films fabricated on glass substrates by using a combination of solid-state reaction and dip coating techniques.
About: This article is published in Journal of Applied Research and Technology.The article was published on 2017-04-01 and is currently open access. It has received 67 citations till now. The article focuses on the topics: Magnetic semiconductor & Dip-coating.
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TL;DR: In this article, the effects of transition metal doping to metal-oxide nanoparticles (TiO2) were studied using a variety of characterization techniques, including X-ray diffraction, Fourier transform-infrared (FTIR), ultraviolet-visible (UV-Vis) spectroscopy, field-emission scanning electron microscopy (FESEM), and vibrating sample magnetometer (VSM).
Abstract: In this research, the effects of transition metal (Ni) doping to metal-oxide nanoparticles (TiO2) were studied. Various weight ratios (5, 10, 15, and 20%) of Ni-to-TiO2 nanoparticles were synthesized using the sol–gel technique. These doped nanoparticles were prepared using titanium butoxide and nickel nitrate as precursors and methanol as a solvent. The effects of Ni doping to TiO2 were examined using a variety of characterization techniques, X-ray diffraction (XRD), Fourier-transform-infrared (FTIR) spectroscopy, ultraviolet–visible (UV–Vis) spectroscopy, field-emission scanning electron microscopy (FESEM), and vibrating sample magnetometer (VSM). The XRD reveals that the Ni-doped TiO2 crystallizes in a tetragonal structure with anatase phase. The particle size and lattice strain were calculated by Williamson–Hall equation. The presence of strong chemical bonding and functional groups at the interface of TiO2 nanoparticles was confirmed by FTIR. The optical properties of undoped and doped samples were recorded by UV–Vis spectroscopy. The saturation magnetization (Ms) was found higher for undoped as compared to doped samples. The surface morphology and the element structure of the Ni-doped TiO2 nanoparticles were examined by FESEM.
70 citations
TL;DR: In this article, the effects of Ni and Cu doping in TiO2 matrix are characterized by XRD, Micro-Raman, FTIR, UV-DRS, PL, and FESEM with EDS.
Abstract: In the present work, Ni2+ and Cu2+ ions are doped with TiO2 using sol–gel technique. The effects of Ni and Cu doping in TiO2 matrix are characterized by XRD, Micro-Raman, FTIR, UV–DRS, PL, and FESEM with EDS. Furthermore, it is analyzed for photocatalytic activity and magnetic applications. From XRD analysis, it is observed that the peaks corresponding to the planes match with the JCPDS data [anatase: 89-4203] of TiO2. The crystallite size of the doped samples is found to be greater than that of TiO2. Micro-Raman analysis shows the confirmation of anatase phase of TiO2. FTIR analysis confirms the presence of functional groups which are presented in the prepared samples. From UV–DRS, the band-gap values of TiO2 and doped TiO2 (Ni2+, Cu2+) are found to be 3.25, 2.48, and 1.25 eV. Photoluminescence (PL) results show an emission edge of Ni- and Cu-doped TiO2 is red shifted which is due to the vacancies of titanium and oxygen imported subsequently during doping. The surface morphology and the elemental composition of Ni- and Cu-doped TiO2 nanoparticles are also analyzed. The photocatalytic activity of all the prepared samples are assessed by methylene blue dye as testing pollutant and visible radiation. The test reveals that Cu–TiO2, Ni–TiO2, and TiO2 show the degradation efficiency of 68.14, 61.04, and 33.32%, thereby showing that the doped TiO2 are more efficient in degrading the pollutant and can be applied for future photocatalytic applications. From VSM analysis, the saturation magnetization of Ni–TiO2 and Cu–TiO2 is found to be weak and can be improved by the synthesis process and the proportion of dopant.
51 citations
03 Oct 2018
TL;DR: In this paper, Ni-doped SnO2 nanoparticles were synthesized by a coprecipitation route and showed superior properties for a series of different applications for different applications.
Abstract: Ni-doped SnO2 nanoparticles were synthesized by a coprecipitation route and showed superior properties for a series of different applications. The 1 atom % Ni-doped SnO2 NPs exhibited excellent ele...
43 citations
TL;DR: In this paper, the structural, morphological, optical and magnetic behavior of non-magnetic element (Cu and Zn) doped TiO2, synthesized via a simple sol-gel technique was investigated.
Abstract: Oxide based dilute magnetic semiconductor materials have been of great interest over the years due to their potential use in spintronic devices. However, the variations in the magnetic behavior of the materials have raised concerns regarding the origin of ferromagnetic properties which still needs to be explored. Manipulation of magnetic behavior in oxide based dilute magnetic semiconductors has become a challenge due to the interplay of intrinsic defects present in the material. TiO2 nanocrystals have been studied largely due to their challenging optical and magnetic properties. The present investigation studies in detail the structural, morphological, optical and magnetic behavior of non-magnetic element (Cu and Zn) doped TiO2, synthesized via a simple sol–gel technique. X-ray diffraction patterns and Raman spectra confirm the anatase phase and high resolution transmission electron microscopic results clearly indicate the formation of highly crystalline nanocrystals in all the samples with particle size ranging from 5–15 nm. Energy dispersive X-ray fluorescence spectroscopic studies reveal the compositional homogeneity of all the investigated samples. The presence of functional groups and molecular interactions were identified by Fourier transform infrared spectroscopy. Optical properties were studied through UV-visible and photoluminescence spectroscopy from which a significant reduction in band gap in Cu-doped TiO2 nanocrystals was found. X-ray photoelectron spectra confirm the presence of Ti3+, Cu2+, Cu+ and Zn2+ in Cu and Zn-doped TiO2 samples. The concept of bound magnetic polarons associated with the vacancy defects at both Ti, Cu, Zn and oxygen sites is used to explain the induced weak ferromagnetic behavior in undoped, Cu and Zn-doped TiO2 at room temperature. The overlapping of bound magnetic polarons could be the source of ferromagnetism irrespective of the non-magnetic nature of the dopant ion. The concentration of bound magnetic polarons is estimated using a Langevin fit and a detailed understanding of the variation of defect mediated magnetic properties is established with the help of PL analysis. A significant reduction in bandgap along with enhanced magnetization observed in the Cu-doped TiO2 material makes it suitable as a potential candidate for spintronics and magneto-optics applications. Room temperature magnetic properties of the Zn doped sample show a diamagnetic tail which is explained based on the defect centers and oxidation states of dopant ions present in the sample which is further verified with the help of XPS results.
39 citations
TL;DR: In this article, the structural, optical and electrical properties of the prepared materials are investigated using XRD, UV-Vis and impedance analyses respectively, and the interfacial charge transport resistances and chemical capacitances of the fabricated DSSCs are evaluated from the EIS investigations and the photovoltaic performance of Ni doped TiO2 based DSSC shows enhanced efficiency up to 4%.
Abstract: Employing the prepared pure TiO2 and Ni doped TiO2 as photoanode material, dye sensitized solar cells (DSSCs) are fabricated with ruthenium complex as dye-sensitizer [Cis-bis(isothiocyanato) bis(2, 2′-bipyridyl-4, 4′-dicarboxylato)ruthenium(II) also called as N3 dye] and LiI as redox electrolyte. In this concern, pure TiO2 and Ni–TiO2 are prepared through sol–gel technique. The structural, optical and electrical properties of the prepared materials are investigated using XRD, UV–Vis and impedance analyses respectively. The XRD pattern reveals pure crystalline anatase phase of pure TiO2 and Ni–TiO2 and the crystallite size was found to be in the range of 7–11 nm. UV–Vis spectroscopy shows the enhancement of absorption spectrum in UV region with red shift was observed by Ni doping. The electron transport properties of the prepared TiO2 and Ni doped TiO2 shows higher conductivity in 3% Ni doped TiO2 confirmed from impedance studies. The interfacial charge transport resistances and chemical capacitances of the fabricated DSSCs are evaluated from the EIS investigations and the photovoltaic performance of Ni doped TiO2 based DSSC shows enhanced efficiency up to 4%.
36 citations
References
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1,049 citations
TL;DR: In this article, the magnetic moment was observed in undoped semiconducting or insulating oxides to become ferromagnetic at room temperature on MgO substrates, where the magnetic field was applied parallel to the film plane.
Abstract: Remarkable room-temperature ferromagnetism was observed in undoped $\mathrm{Ti}{\mathrm{O}}_{2}$, $\mathrm{Hf}{\mathrm{O}}_{2}$, and ${\mathrm{In}}_{2}{\mathrm{O}}_{3}$ thin films. The magnetic moment is rather modest in the case of ${\mathrm{In}}_{2}{\mathrm{O}}_{3}$ films on MgO substrates (while on ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ substrates, it is negative showing diamagnetism) when the magnetic field was applied parallel to the film plane. In contrast, it is very large in the other two cases (about 20 and $30\phantom{\rule{0.3em}{0ex}}\mathrm{emu}∕{\mathrm{cm}}^{3}$ for $200\text{\ensuremath{-}}\mathrm{nm}$-thick $\mathrm{Ti}{\mathrm{O}}_{2}$ and $\mathrm{Hf}{\mathrm{O}}_{2}$ films, respectively). Since bulk $\mathrm{Ti}{\mathrm{O}}_{2}$, $\mathrm{Hf}{\mathrm{O}}_{2}$, and ${\mathrm{In}}_{2}{\mathrm{O}}_{3}$ are clearly diamagnetic, and moreover, there are no contaminations in any substrate, we must assume that the thin film form, which might create necessary defects or oxygen vacancies, would be the reason for undoped semiconducting or insulating oxides to become ferromagnetic at room temperature.
772 citations
TL;DR: Using density functional theory (DFT) calculations within the generalized gradient corrected approximation, this article investigated various structural models of carbon impurities in both anatase and rutile polymorphs of TiO2 and analyzed the associated modifications of the electronic band structure.
Abstract: Recent experimental studies have determined that carbon doping dramatically improves the photocatalytic activity of TiO2 in the visible-light region. Using density functional theory (DFT) calculations within the generalized gradient corrected approximation, we investigate various structural models of carbon impurities in both the anatase and rutile polymorphs of TiO2 and analyze the associated modifications of the electronic band structure. We compare the stability of all these diverse species on the basis of their energy of formation as a function of the oxygen chemical potential, which determines whether the system is in an oxidizing or reducing environment. At low carbon concentrations, we find that, under oxygen-poor conditions, substitutional (to oxygen) carbon and oxygen vacancies are favored, whereas, under oxygen-rich conditions, interstitial and substitutional (to Ti) C atoms are preferred. Higher carbon concentrations undergo an unexpected stabilization caused by multidoping effects, interpreted...
655 citations
TL;DR: Ferromagnetism with T(C) > 350 K is observed in aggregated nanocrystals of Co(2+):ZnO that unambiguously demonstrates the existence of intrinsic high-T(C), ferromagnetsism in this class of DMSs.
Abstract: We report a method for the preparation of colloidal ZnO-diluted magnetic semiconductor quantum dots (DMS-QDs) by alkaline-activated hydrolysis and condensation of zinc acetate solutions in dimethyl sulfoxide (DMSO). Mechanistic studies reveal that Co2+ and Ni2+ dopants inhibit nucleation and growth of ZnO nanocrystals. In particular, dopants are quantitatively excluded from the critical nuclei but are incorporated nearly isotropically during subsequent growth of the nanocrystals. The smaller nanocrystal diameters that result upon doping are explained by the Gibbs−Thompson relationship between lattice strain and crystal solubility. We describe methods for cleaning the nanocrystal surfaces of exposed dopants and for redispersion of the final DMS-QDs. Homogeneous substitutional doping is verified by high-resolution low-temperature electronic absorption and magnetic circular dichroism (MCD) spectroscopies. A “giant Zeeman effect” is observed in the band gap transition of Co2+:ZnO DMS-QDs. MCD and Zeeman spect...
621 citations
TL;DR: In this article, the authors presented a systematic study on two different preparation methods for titanium dioxide with silver, and found that the latter produces a more effective photocatalytic material (6-50% improvement in catalytic efficiency), which is attributed to the fact that the silver is homogeneously dispersed throughout the material.
Abstract: This paper presents a systematic study on two different preparation methods for titanium dioxide with silver. The silver can be incorporated by irradiating the reaction mixture during preparation to reduce silver ion to silver metal or by direct calcination of the sol–gel material to decompose silver nitrate to silver. Of the two methods, we found the latter produces a more effective photocatalytic material (6–50% improvement in catalytic efficiency), which is attributed to the fact that the silver is homogeneously dispersed throughout the material. The efficiency of the materials were examined using a Q-Sun solar simulator (visible light) and in Dublin summer sunlight (latitude 54°N). In both cases, the addition of increasing amounts of silver, for both batches of samples, significantly increases the rate of degradation of a model dye, rhodamine 6G (R6G), increasing the rate of degradation from 0.06 min−1 for TiO2 to 0.34 min−1 for 5 mol% Ag–TiO2. This is attributed to the increasing visible absorption capacity due to the presence of silver nanoparticles.
567 citations