Chandran Sudakar

Bio: Chandran Sudakar is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topic(s): Magnetization & Thin film. The author has an hindex of 32, co-authored 140 publication(s) receiving 3204 citation(s). Previous affiliations of Chandran Sudakar include Wayne State University & Indian Institute of Science.

Tunable Bandgap in BiFeO 3 Nanoparticles: The Role of Microstrain and Oxygen Defects

Abstract: We demonstrate a tunable bandgap from 2.32 eV to 2.09 eV in phase-pure BiFeO3 by controlling the particle size from 65 nm to 5 nm. Defect states due to oxygen and microstrain show a strong dependence on BiFeO3 particle size and have a significant effect on the shape of absorbance curves. Oxygen-defect induced microstrain and undercoordinated oxygen on the surface of BiFeO3 nanoparticles are demonstrated via HRTEM and XPS studies. Microstrain in the lattice leads to the reduction in rhombohedral distortion of BiFeO3 for particle sizes below 30 nm. The decrease in band gap with decreasing particle size is attributed to the competing effects of microstrain, oxygen defects, and Coulombic interactions.

Highly dispersed phase of SnO2 on TiO2 nanoparticles synthesized by polyol-mediated route: Photocatalytic activity for hydrogen generation

Abstract: TiO 2 –SnO 2 mixed oxides (Ti:Sn = 98:2 (TS2), 95:5 (TS5) and 90:10 (TS10) by atomic weight) of large surface area and small particle size, in which SnO 2 is in a dispersed phase on TiO 2 , have been synthesized by a polyol-mediated route. Characterization by various techniques has shown that a highly dispersed phase of SnO 2 on anatase TiO 2 is formed in TS2 sample. No separate discernible phases corresponding to cassiterite SnO 2 or rutile TiO 2 is seen in TS2 sample, whereas rutile TiO 2 and SnO 2 are observed besides the anatase phase of TiO 2 in TS5 and TS10 samples. The average particle size of the mixed oxide samples is ∼20 nm. All samples absorb visible light and the onset of absorption was ∼425 nm. These mixed oxides show emission from defect levels arising due to the anion vacancies present in TiO 2 . The visible light absorption of these samples is attributed to the presence of defect levels in the bandgap of TiO 2 . Photocatalytic activity of these samples for hydrogen generation from water using methanol as sacrificial reagent was studied under sunlight type radiation. The results indicate that mixed oxides have better activity compared to pure TiO 2 synthesized by the same method and the activity decreases with increasing SnO 2 concentration in TiO 2 . The enhanced activity of TS2 sample is ascribed to the efficient charge separation from TiO 2 to SnO 2 owing to the high dispersion of SnO 2 in TiO 2 . The decreased photocatalytic activity with increased SnO 2 concentration is due to the aggregation of SnO 2 on TiO 2 , which results in relatively poor dispersion of SnO 2 and decreased charge transfer efficiency, but still maintains better photocatalytic activity compared to TiO 2 . In addition loading Pd co-catalyst produces a pronounced increase in the hydrogen yield due to the accumulation of electrons in the metal from the TiO 2 and SnO 2 semiconductors and the increased reductive power of the Pd loaded mixed oxide nanoparticles.

Structural, magnetic, and electrical studies on polycrystalline transition-metal-doped BiFeO3 thin films

Abstract: We have synthesized a range of transition-metal-doped BiFeO3 thin films on conducting silicon substrates using a spin-coating technique from metal–organic precursor solutions. Bismuth, iron and transition-metal–organic solutions were mixed in the appropriate ratios to produce 3% transition-metal-doped samples. X-ray diffraction studies show that the samples annealed in a nitrogen atmosphere crystallize in a rhombohedrally distorted BiFeO3 structure with no evidence for any ferromagnetic secondary phase formation. We find evidence for the disappearance of the 404 cm−1 Raman mode for certain dopants indicative of structural distortions. The saturation magnetization of these BiFeO3 films has been found to increase on doping with transition metal ions, reaching a maximum value of 8.5 emu cm−3 for the Cr-doped samples. However, leakage current measurements find that the resistivity of the films typically decreases with transition metal doping. We find no evidence for any systematic variation of the electric or magnetic properties of BiFeO3 depending on the transition metal dopant, suggesting that these properties are determined mainly by extrinsic effects arising from defects or grain boundaries.

Ferromagnetism induced by planar nanoscale CuO inclusions in Cu-doped ZnO thin films

Abstract: We report ferromagnetism above $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ in $\mathrm{Zn}\mathrm{O}:x\mathrm{Cu}$ ($x$ in at. %) sputtered thin films. For $xl1$, a large magnetic moment of $1.6\phantom{\rule{0.3em}{0ex}}{\ensuremath{\mu}}_{B}∕\mathrm{Cu}$ was observed, which decreases monotonically with increasing $x$. We find evidence that the ferromagnetic moment is due to Cu-O planar nanophase inclusions in ZnO basal planes. The presence of CuO nanophase is confirmed by transmission electron microscopy, x-ray diffraction, and Raman spectroscopy studies. These inclusions are present even for $xl3$, where Cu-O structures of a few nanometers in size are observed. Field-cooled and zero-field-cooled magnetization measurements show a bifurcation for temperatures below $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$.

Raman spectroscopic studies of oxygen defects in Co-doped ZnO films exhibiting room-temperature ferromagnetism

Abstract: The optical properties, Raman spectra, and magnetization of Zn1−xCoxO (0≤x<0.1) thin films are reported. Optical transmission spectra confirm the substitution of Co2+ cations for Zn2+ ions at the tetrahedral sites of ZnO. Raman spectra of films annealed in air show an additional broad vibrational mode, attributed to disordered –Zn–O–Co– local vibrations. These modes disappear on vacuum annealing, suggesting the formation of oxygen vacancies close to the dopant sites (–Zn––Co–). Magnetization measurements show that air-annealed films lack significant moment, whereas vacuum-annealed samples with intermediate Co concentrations (0.012

Semiconductor-based Photocatalytic Hydrogen Generation

Abstract: 2.3. Evaluation of Photocatalytic Water Splitting 6507 2.3.1. Photocatalytic Activity 6507 2.3.2. Photocatalytic Stability 6507 3. UV-Active Photocatalysts for Water Splitting 6507 3.1. d0 Metal Oxide Photocatalyts 6507 3.1.1. Ti-, Zr-Based Oxides 6507 3.1.2. Nb-, Ta-Based Oxides 6514 3.1.3. W-, Mo-Based Oxides 6517 3.1.4. Other d0 Metal Oxides 6518 3.2. d10 Metal Oxide Photocatalyts 6518 3.3. f0 Metal Oxide Photocatalysts 6518 3.4. Nonoxide Photocatalysts 6518 4. Approaches to Modifying the Electronic Band Structure for Visible-Light Harvesting 6519

Understanding TiO2 photocatalysis: mechanisms and materials.

Abstract: Jenny Schneider,*,† Masaya Matsuoka,‡ Masato Takeuchi,‡ Jinlong Zhang, Yu Horiuchi,‡ Masakazu Anpo,‡ and Detlef W. Bahnemann*,† †Institut fur Technische Chemie, Leibniz Universitaẗ Hannover, Callinstrasse 3, D-30167 Hannover, Germany ‡Faculty of Engineering, Osaka Prefecture University, 1 Gakuen-cho, Sakai Osaka 599-8531, Japan Key Lab for Advanced Materials and Institute of Fine Chemicals, East China University of Science and Technology, Shanghai 200237, China

Ferromagnetic materials

Abstract: In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Advanced Nanoarchitectures for Solar Photocatalytic Applications

Abstract: UV-Visible ار راد ن .د TiO2 ( تیفرظ راون مان هب نورتکلا یاراد یژرنا زارت لماش VB و ) رگید زارت ی یژرنا اب ( ییاناسر راون مان هب نورتکلا زا یلاخ و رتلااب VB یم ) .دشاب ت ود نیا نیب یژرنا توافت یژرنا فاکش زار ، پگ دناب هدیمان یم .دوش هک ینامز زا نورتکلا لاقتنا VB هب VB یم ماجنا دریگ ، TiO2 اب ودح یژرنا بذج د ev 2 / 3 ، نورتکلا تفج کی دیلوت یم هرفح .دیامن و نورتکلا هرفح ی نا اب هدش دیلوت یم کرتشم حطس هب لاقت ثعاب دناوت شنکاو ماجنا اه یی ددرگ . TiO2 دربراک ،دراد یدایز یاه هلمج زا یم ناوت اوه یگدولآ هیفصت یارب (CO2) و بآ و ... نآ زا هدافتسا درک .

Titanium dioxide-based nanomaterials for photocatalytic fuel generations.

Abstract: Generations Yi Ma,† Xiuli Wang,† Yushuai Jia,† Xiaobo Chen,‡ Hongxian Han,*,† and Can Li*,† †State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences and Dalian National Laboratory for Clean Energy, 457 Zhongshan Road, Dalian 116023, China ‡Department of Chemistry, College of Arts and Sciences, University of Missouri-Kansas City, 5100 Rockhill Road, Kansas City, Missouri 64110, United States