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Showing papers by "Chandran Sudakar published in 2012"


Journal ArticleDOI
TL;DR: In this paper, the authors proposed a method to tune the band gap in nanocomposite systems over a wide energy range by changing the composition and annealing temperature of SnO 2 and MgO.

53 citations


Journal ArticleDOI
TL;DR: In this article, the synthesis of undoped and Sc 3+ doped Bi 2 Fe 4 O 9 nanoparticles using sonochemical technique was reported and X-ray diffraction reveals that all samples are single phase with no impurities detected.

37 citations


Journal ArticleDOI
TL;DR: The results reveal unambiguously that atomic point defects exist in these RTFM thin films and provide strong support for defect-mediated ferromagnetism in Cu-doped ZnO thin films.
Abstract: We report a comprehensive study of the defects in room-temperature ferromagnetic (RTFM) Cu-doped ZnO thin films using x-ray absorption spectroscopy. The films are doped with 2 at.% Cu, and are prepared by reactive magnetron sputtering (RMS) and pulsed laser deposition (PLD), respectively. The results reveal unambiguously that atomic point defects exist in these RTFM thin films. The valence states of the Cu ions in both films are 2+. In the film prepared by PLD, the oxygen vacancies (VO) form around both Zn ions and Cu ions in the hexagonal wurtzite structure. Upon annealing of the film in O2, the VO population reduces and so does the RTFM. In the film prepared by RMS, the VOs around Cu ions are not detected, and the VO population around Zn ions is also smaller than in the PLD-prepared film. However, zinc vacancies (VZn) are evidenced. Given the low doping level of spin-carrying Cu ions, these results provide strong support for defect-mediated ferromagnetism in Cu-doped ZnO thin films.

25 citations


Journal ArticleDOI
TL;DR: In this article, an ethanol-based sol-gel method using lauric acid (LA) as a surfactant for high specific capacity lithium-ion battery cathode material was proposed.
Abstract: We report synthesis of nanosize LiFePO4 and C-LiFePO4 powders with a narrow particle size distribution (20–30 nm) by ethanol-based sol–gel method using lauric acid (LA) as a surfactant for high specific capacity lithium-ion battery cathode material. X-ray diffraction measurements demonstrated that the samples were single-phase materials without any impurity phases. The average crystallite size was found to decrease slightly from 29 nm to approximately 23 nm with carbon coating. The ratio of the Raman D-band (~1350 cm−1) to G-band (~1590 cm−1) intensities (ID/IG) and electronic conductivity of these materials show strong dependence on the amount of surfactant coverage. Remarkably, cell prepared with carbon-coated LiFePO4 synthesized using 0.25 M solution of LA showed a very large specific capacity approaching the theoretical limit of 170 mAh/g, in stark contrast to the specific capacity of cell consisting of pure of LiFePO4 (~75 mAh/g) measured at the same C/2 discharge rate.

15 citations


Book ChapterDOI
01 Jan 2012
TL;DR: In this article, the authors provide a brief overview of some of the new properties that can emerge in nanostructured oxides due to the presence of defects, including the development of metallic conductivity over a broad range of temperatures in oxygen vacancy defect-rich insulating oxide films.
Abstract: The properties of functional metal oxide nanostructures can be highly susceptible to the presence of defects. The defect concentration in these systems, which have exceedingly large surface to volume ratios, can be very high, potentially leading to qualitatively new phenomena beyond perturbing the existing characteristics. This chapter is focused on providing a brief overview of some of the new properties that can emerge in nanostructured oxides due to the presence of defects. This includes the development of metallic conductivity over a broad range of temperatures in oxygen vacancy defect-rich insulating oxide films. High charge carrier concentrations can also produce new collective optical phenomena, such as sharp plasmon resonances, as well as features in the photoluminescence. Remarkably, defects in semiconducting oxide nanostructures may also promote high temperature ferromagnetism, although there remains considerable debate concerning the underlying origins of this effect, including concerns about extrinsic effects. There are, however, a number of significant experimental observations on ferromagnetism in defect-rich semiconducting oxide nanomaterials, including direct low temperature measurements of the spin polarization. The plethora of physical phenomena associated with defects in metal oxide nanostructures allows the exciting possibility of introducing desired functionalities into these systems through controlled defect engineering.

6 citations