Department Of Physics

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Author: search.filters.author.Yadav, KamleshHas files: Yes

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    Optical properties of nanocrystallite films of ?-Fe2O3 and ?-Fe2-xCrxO3 (0.0 ? x ? 0.9) deposited on glass substrates
    (Institute of Physics Publishing, 2017) Kumar, Ajay; Yadav, Kamlesh
    ?-Fe2O3 films are deposited on fluorine-doped tin oxide (FTO) and indium-doped tin oxide (ITO) substrates for 1, 4 and 6 min using a spray pyrolysis technique. We also deposited ?-Fe2-xCrxO3 (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.7 and 0.9) films on the FTO substrate for a deposition time of 35 s. The structural and optical properties of these films were then studied. The x-ray diffraction (XRD) patterns show that all the films are crystalline in nature with a hexagonal crystal structure. The average grain size and unit cell volume were calculated using XRD data. It is found that the average grain size and unit cell volume increase with an increasing film thickness and Cr-doping concentration. The value of strain decreases with an increasing film thickness and Cr-doping content. It is also found that films with the same deposition time on the ITO substrate are more crystalline than on the FTO substrate. Furthermore, the average grain size is obtained from field emission scanning electron microscopy (FESEM) images. FESEM analysis confirms that the average grain size increases with the film thickness and Cr-doping concentration. The optical absorption spectra of the films show that the absorbance increases with an increasing deposition time and Cr concentration. The energy band gap (Eg) of all the films has been calculated using Tauc's relation. A narrowing of the band gap was observed with an increase in film thickness and Cr-doping content. The reduction of the band gap with the increase in film thickness of the films deposited on the ITO substrate is larger than for the film deposited on the FTO substrate. The refractive index is also obtained from the absorption spectra of the films using the Moss relation: n = 4 (k/Eg), where k =108 eV. The refractive index decreases with an increase in the optical band gap. The band gaps of the films are also calculated from the FTIR spectra. This is in good agreement with the UV data. The correlation between the structural and optical properties of the deposited films has been discussed.
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    Effect of lattice defects on the structural and optical properties of Ni1 − XAgXO (where X = 0.0, 0.01, 0.03, 0.05, 0.10 and 0.15) nanoparticles
    (Springer, 2018) Sharma, Rohit; Yadav, Kamlesh
    The Ni1 − XAgXO (where X = 0, 0.01, 0.02, 0.03, 0.05, 0.10, and 0.15) nanoparticles are synthesized by sol–gel technique. The effects of Ag-doping in NiO nanoparticle on the structural and optical properties are studied. XRD analysis confirms that the prepared samples are single phase and oxygen deficient in nature. The unit cell volume decreases with the increase in the Ag-doping content. The crystallite size decreases from 23 to 19 nm with increasing the Ag-doping content up to X = 0.10. The strain increases with increase in Ag-doping concentration. FESEM analysis confirms that the pure sample of NiO is quasi-spherical and this shape is deformed as the Ag content increases in the NiO samples. The increase in the agglomeration of nanoparticles with the increase in doping content is also observed. UV–Visible analysis shows that the calculated optical band gap of the pure NiO sample is 3.70 eV which is less than the reported value 4.42 eV of NiO nanoparticles. The optical band gap increases as the Ag-doping content increases in the host NiO lattice. The change in band gap is increased rapidly for the X = 0.01 sample and then become slow for the rest of the samples. FT–IR analysis gives all the information regarding the functional group present in the samples. The effect of disorder created due to Ag-doping in NiO lattice leads to the formation of lattice defects and affects the structural and optical properties, which have been discussed in this paper in detail.
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    Thickness-dependent magnetic and transport properties of La0.5Sr0.5MnO3 thin films deposited by DC magnetron sputtering on the LaAlO3 substrate
    (Springer Verlag, 2018) Yadav, Kamlesh; Singh, H. K.; Maurya, K. K.; Varma, G. D.; Yadav, K.; Singh, H.K.; Maurya, K.K.; Varma, G.D.
    Thickness-dependent structural, magnetic and transport properties of La0.5Sr0.5MnO3 (LSMO) thin films have been studied. A series of the LSMO films with thickness 30, 60, 125 and 300?nm have been deposited on the LaAlO3 substrate using DC magnetron sputtering. The paramagnetic to ferromagnetic transition at TC is followed by antiferromagnetic ordering at TN in all films. It is also found that all LSMO films have TC lower than that of bulk LSMO. A small variation of TC is observed on increasing the film thickness. However, TN is found to rise with increase in the film thickness. The 60?nm-thick film shows a wide insulator to metal transition. The resistivity above 240?K of the films with various thicknesses is consistent with a small polaronic hopping conductivity. The polaronic formation energy EA rises with the increase of the film thickness except for 60?nm thin film, where a small decline in EA is observed. The correlation between observed structural, magnetic and electrical properties with the thickness of the films has been discussed in this paper. ? 2017, Springer-Verlag GmbH Germany, part of Springer Nature.