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Kovendhan, M.,Paul Joseph, D.,Manimuthu, P.,Sendilkumar, A.,Karthick, S.N.,Sambasivam, S.,Vijayarangamuthu, K.,Kim, H.J.,Choi, B.C.,Asokan, K.,Venkateswaran, C.,Mohan, R. Elsevier 2015 Current Applied Physics Vol.15 No.5
Lithium (Li) (0-5 wt%) doped V<SUB>2</SUB>O<SUB>5</SUB> thin films were spray deposited at 450 <SUP>o</SUP>C onto ITO substrates. Structural analysis using X-ray diffraction and Raman spectroscopy revealed orthorhombic phase of the films. In addition to the V<SUB>2</SUB>O<SUB>5</SUB> phase, presence of VO<SUB>2</SUB> peaks due to high deposition temperature is also evident from structural and optical characterization. The non-stoichiometric nature of the films due to loss of the terminal O atom was confirmed from Raman spectroscopy. The direct band gap, indirect bandgap, and phonon energies were also calculated from optical studies. Different charge states of vanadium ions present in the film were identified from X-ray photoelectron spectroscopy study. Results from cyclic voltammetry experiments reflected significant differences between the undoped and Li doped V<SUB>2</SUB>O<SUB>5</SUB> samples. Transport properties by Hall-effect measured at room temperature indicated significant increase in conductivity, carrier concentration and mobility of V<SUB>2</SUB>O<SUB>5</SUB> thin films on doping with Li. A Dye Sensitized Solar Cell (DSSC) was fabricated using mobility enhanced 5 wt% Li doped V<SUB>2</SUB>O<SUB>5</SUB> film as photoanode and its efficiency was found to be 2.7%. A simple electrochromic cell is fabricated using undoped V<SUB>2</SUB>O<SUB>5</SUB> thin film to demonstrate the colour change.
Structural, vibrational, and enhanced magneto-electric coupling in Ho-substituted BiFeO<sub>3</sub>
Muneeswaran, Muniyandi,Lee, Seung Hoon,Kim, Dong Hun,Jung, Beon Sung,Chang, Seo Hyoung,Jang, Jae-Won,Choi, Byung Chun,Jeong, Jung Hyun,Giridharan, N.V.,Venkateswaran, C. Elsevier 2018 JOURNAL OF ALLOYS AND COMPOUNDS Vol.750 No.-
<P><B>Abstract</B></P> <P>The effect of Holmium (Ho) substitution in BiFeO<SUB>3</SUB> [Bi<SUB>1-x</SUB>Ho<SUB>x</SUB>FeO<SUB>3</SUB> (x = 0.00, 0.05, 0.10, 0.15, 0.18, and 0.20)] ceramics is reported. The X-ray diffraction study shows composition-driven rhombohedral-to-orthorhombic (<I>R</I>3<I>c</I> to <I>Pnma</I>) phase transition for Bi<SUB>1-x</SUB>Ho<SUB>x</SUB>FeO<SUB>3</SUB> (x = 0.15, 0.18, and 0.20) which is confirmed by Reitveld refinement. Raman spectra of Bi<SUB>1-x</SUB>Ho<SUB>x</SUB>FeO<SUB>3</SUB> (x = 0.00, 0.05, and 0.10) belong to the rhombohedral (<I>R</I>3<I>c</I>) structure. Further increasing the Ho<SUP>3+</SUP> concentration in a BiFeO<SUB>3</SUB> (BFO) system revealed that Raman modes of Bi<SUB>1-x</SUB>Ho<SUB>x</SUB>FeO<SUB>3</SUB> (x = 0.15, 0.18 and 0.20) were assigned to an orthorhombic (<I>pnma</I>) structure, which is confirmed by the Rietveld analysis of X-ray diffraction data and TEM analysis. Ferroelectric studies show that the remnant polarization (P<SUB>r</SUB>) gradually decreases for Bi<SUB>1-x</SUB>Ho<SUB>x</SUB>FeO<SUB>3</SUB> (x = 0.15, 0.18, and 0.20), confirming the transformation from polar to non-polar systems. Magnetic measurement shows ferromagnetic behavior observed for Bi<SUB>1-x</SUB>Ho<SUB>x</SUB>FeO<SUB>3</SUB> (x = 0.10 and 0.20) samples. Further, the magneto-electric coupling is measured in terms of magneto-capacitance of Ho<SUP>3+</SUP>-substituted BiFeO<SUB>3</SUB> samples.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Ho<SUP>3+</SUP> substituted BFO ceramics were synthesized by a solid-state reaction. </LI> <LI> Structural transformation from rhombohedral (<I>R</I>3<I>c</I>) to orthorhombic (<I>Pbnm</I>). </LI> <LI> Higher Ho<SUP>3+</SUP> substituted BFO is assigned orthorhombic (<I>Pbnm</I>) by Raman studies. </LI> <LI> Enhanced magneto-electric coupling observed in Ho<SUP>3+</SUP> substituted BFO samples. </LI> </UL> </P>
D. Paul Joseph,C. Venkateswaran,S. Sambasivam,최병춘 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.3
Pure CuO and CuO:Fe (10%) thin films were spray deposited on glass, silicon and quartz substrates at 500 ℃. XRD patterns confirmed a monoclinic structure with cubic CuFe<sub>2</sub>O<sub>4</sub> impurities. Surface morphology smoothed out on doping with Fe. The direct and the indirect band gaps of pure CuO and CuO:Fe (10%) films estimated from the spectral transmittance data indicated blue and red shifts respectively. X-ray photoelectron spectroscopy revealed the charge states of the elements. The activation energy for conduction was reduced on doping with Fe as estimated from an Arrhenius plot of the temperature-dependent resistivity. The magnetization of the CuO:Fe (10%) films at 300 K showed a hysteresis behavior with large coercivity. The large variation in the coercivity of the films due to pinned- type magnetic behavior may be useful for multilayer switching device applications.
R. Rathika,M. Kovendhan,D. Paul Joseph,K. Vijayarangamuthu,A. Sendil Kumar,C. Venkateswaran,K. Asokan,S. Johnson Jeyakumar 한국원자력학회 2019 Nuclear Engineering and Technology Vol.51 No.8
Spray deposited Molybdenum trioxide (MoO3) thin film of thickness nearly 379 nm were irradiated with 200 MeV Ag15þ ion beam at different fluences (Ø) of 5 1011,1 1012,5 1012 and 1 1013 ions/cm2. The X-ray diffraction (XRD) pattern of the pristine film confirms orthorhombic structure and the crys-tallinity decreased after irradiation with the fluence of 5 1011 ions/cm2 due to irradiation induced defects and became amorphous at higher fluence. In pristine film, Raman modes at 665, 820, 996 cm1 belong to MoeO stretching, 286 cm1 belong to MoeO bending mode and those below 200 cm1 are associated with lattice modes. Raman peak intensities decreased upon irradiation and vanished completely for the ion fluence of 5 1012 ions/cm2. The percentage of optical transmittance of pristine film was nearly 40%, while for irradiated films it decreased significantly. Red shift was observed for both the direct and indirect band gaps. The pristine film surface had densely packed rod like structures with relatively less porosity. Surface roughness decreased significantly after irradiation. The electrical trans-port properties were also studied for both the pristine and irradiated films by Hall effect. The results are discussed.
Rathika, R.,Kovendhan, M.,Joseph, D. Paul,Pachaiappan, Rekha,Kumar, A. Sendil,Vijayarangamuthu, K.,Venkateswaran, C.,Asokan, K.,Jeyakumar, S. Johnson Korean Nuclear Society 2020 Nuclear Engineering and Technology Vol.52 No.11
Swift heavy ion (SHI) beam irradiation can generate desirable defects in materials by transferring sufficient energy to the lattice that favours huge possibilities in tailoring of materials. The effect of Ag<sup>15+</sup> ion irradiation with energy 200 MeV on spray deposited V<sub>2</sub>O<sub>5</sub> thin films of thickness 253 nm is studied at various ion doses from 5 × 10<sup>11</sup> to 1 × 10<sup>13</sup> ions/㎠. The XRD results of pristine film confirmed orthorhombic structure of V<sub>2</sub>O<sub>5</sub> and its average crystallite size was found to be 20 nm. The peak at 394 cm<sup>-1</sup> in Raman spectra confirmed O-V-O bonding of V<sub>2</sub>O<sub>5</sub>, whereas 917 cm<sup>-1</sup> arise because of distortion in stoichiometry by a loss of oxygen atoms. Raman peaks vanished completely above the ion fluence of 5 × 10<sup>12</sup> ions/㎠. Optical studies by UV-Vis spectroscopy shows decrement in transmittance with an increase in ion fluence up to 5 × 10<sup>12</sup> ions/㎠. The red shift is observed both in the direct and indirect band gaps until 5 × 10<sup>12</sup> ions/㎠. The surface topography of the pristine film revealed sheath like structure with randomly distributed spherical nano-particles. The roughness of film decreased and the density of spherical nanoparticles increased upon irradiation. Irradiation improved the conductivity significantly for fluence 5 × 10<sup>11</sup> ions/㎠ due to band gap reduction and grain growth.
M. Kovendhan,D. Paul Joseph,P. Manimuthu,A. Sendilkumar,S.N. Karthick,S. Sambasivam,K. Vijayarangamuthu,김희제,최병춘,K. Asokan,C. Venkateswaran,R. Mohan 한국물리학회 2015 Current Applied Physics Vol.15 No.5
Lithium (Li) (0-5 wt%) doped V2O5 thin films were spray deposited at 450 ℃ onto ITO substrates. Structural analysis using X-ray diffraction and Raman spectroscopy revealed orthorhombic phase of the films. In addition to the V2O5 phase, presence of VO2 peaks due to high deposition temperature is also evident from structural and optical characterization. The non-stoichiometric nature of the films due to loss of the terminal O atom was confirmed from Raman spectroscopy. The direct band gap, indirect bandgap, and phonon energies were also calculated from optical studies. Different charge states of vanadium ions present in the film were identified from X-ray photoelectron spectroscopy study. Results from cyclic voltammetry experiments reflected significant differences between the undoped and Li doped V2O5 samples. Transport properties by Hall-effect measured at room temperature indicated significant increase in conductivity, carrier concentration and mobility of V2O5 thin films on doping with Li. A Dye Sensitized Solar Cell (DSSC) was fabricated using mobility enhanced 5 wt% Li doped V2O5 film as photoanode and its efficiency was found to be 2.7%. A simple electrochromic cell is fabricated using undoped V2O5 thin film to demonstrate the colour change.