Proceedings of National Laser Symposium (NLS-22), Manipal University, Manipal. 8-11 Jan 2014
Structural, Optical and Dielectric Properties of Fe Doped CuO Nanoparticles S .Dhanuskodi, M.Manikandan, K.Karthik School of Physics, Bharathidasan University, Tiruchirappalli-620024,Tamil Nadu, India. E-mail:
[email protected] Abstract: Undoped and Fe doped CuO nanoparticles were prepared by sol-gel method with different concentration (x=0, 0.1, 0.3%) at 300˚C. The obtained nanoparticles were characterised by XRD, SEM with EDAX spectra, UV-Visible, FL and Dielectric properties. XRD pattern exhibit the presence of cupric oxide (CuO) with monoclinic phase. The observed shift in the absorption edge from 204 to 557 nm with (pure CuO) to 1.0eV (CuO: Fe 1%) and 0.9eV (CuO: Fe 3%). From the FL spectra the peak absorbed at 823nm, the band gap is 1.5eV. The dielectric constant and loss decreases with an increasing frequency at room temperature for pure CuO. Introduction Transition metal oxide nanomaterial have special physicochemical properties arising from the quantum size effect and high specific surface area, Copper Oxide (1.2 – 1.5 eV) has tremendous applications such as gas sensor, lithium batteries, solar cells, biomaterial, biomedicine, photo-catalysis, optics, spintronics [1,2]. In this work nanoparticles of CuO with Fe concentration were successfully synthesized via sol-gel method and it’s to structural and optical properties were studied. Experimental For the synthesis of CuO nanoparticles in sol-gel process, 5 gm of Cu (NO3)2.3H2O was dissolved in 20 ml of methanol. The solution was stirred for 1 hour to obtain homogeneous solution and kept for 2 days for gel formation. Then the gel was dried at 200℃ in an oven for 2 hours, and calcined at 300℃ for 1 hour code C1. 0.1 wt % and 0.3 wt % of Fe (NO3)3.9H2O was added as dopant for C2 and C3. Results and Discussion Structural Powder XRD for Undoped and Fe- doped CuO were recorded in the range of 2θ between 30˚ and 80˚. The specific crystallographic planes confirmed that the formation of the CuO (space group C2/c) monoclinic phase matches with the standard JCPDS card No.45-0937) [3]. The average crystallite size of Fe-doped CuO is found. Table 1 show that the crystallite size, strain %, and lattice parameters of CuO nanoparticles.
Proceedings of National Laser Symposium (NLS-22), Manipal University, Manipal. 8-11 Jan 2014
Fig. 2 SEM images of undoped and Fe doped CuO nanoparticles
Fig. 1 X-Ray diffraction undoped and Fe doped CuO nanoparticles
Strain %
Lattice parameter
β
17
0.0032
a=4.6850, b=3.4187,c=5.1101Å
99.57
C2
21
0.0021
a=4.6899, b=3.4269,c=5.1311Å
99.55
C3
23
0.0012
a=4.6953, b=3.3389,c=5.1153Å
99.06
Sample
Crystallite size
name
D nm
C1
Table 1: XRD data Fe doped CuO Nanoparticles
Morphological Observation Fig. 2 shows the SEM images of undoped and Fe doped CuO nanoparticles. The particles are agglomerated. Fig 3 confirms the presence of Fe in CuO. The weight percentage is shown in Table 2.
Element OK
Weight (%) 23.59
Cu K
76.41
Total
100.00
Element OK Cu K Fe K Totals
Weight (%) 14.71 81.63 3.65 100.00
Element OK
Weight (%) 9.39
Cu K
62.65
Fe K Total
27.96 100.00
Fig 3 EDAX spectrum of undoped and Fe doped CuO Table 2: EDAX of undoped and Fe doped CuO
Proceedings of National Laser Symposium (NLS-22), Manipal University, Manipal. 8-11 Jan 2014 Optical Investigations The UV-Vis spectrum was recorded between190 and 1100 nm at room temperature (Fig. 4.) The optical band gap was calculated using Tauc relation by plotting (αhν)1/2 against hν and by extrapolating the curve on the photon energy axis. The indirect bandgap energy for C1 is 1.5eV which is in good agreement. Moreover, with increasing Fe doping concentration, the energy gap is 1.0eV for 0.1wt% Fe and 0.9eV for 0.3 wt% Fe (fig 5).
2.5
C1 C2 C3
Absorbance
2.0 1.5 1.0 0.5 0.0 200
400
600
800
1000
1200
Wavelength (nm)
Fig 4 UV-Visible of a) undoped b) 0.1wt % Fe c) 0.3wt % Fe CuO nanoparticles 30
C3
C2
20
20
0
(eV/m)2 (ahν )
(ahν )
10
1/2
1/2 (eV/m)2
(eV/m)2
20
1/2
(ahν )
30
30
C1
10
10
0
0
1
2
3
hν (eV)
4
1
2
3
1
4
2
3
4
5
hν (eV)
hν (eV)
Fig 5 Tauc plot a) undoped b) 0.1 wt% Fe c) 0.3 wt % Fe CuO nanoparticles
Fluorescence spectra 4
C1 C2 C3
Intensity (a.u)
3
2
1
0 550
600
650
700
750
800
850
900
950
Wavelength (nm)
Fig.6 FL Spectra a) undoped b) 0.1 wt % Fe c) 0.3 wt % Fe CuO nanoparticles
The room temperature Fluorescence spectra (FL) C1, C2 and C3 (Fig. 6).The prepared powder was excited at 550 nm and the emission peak was observed at 823 nm. The intensity of this FL band increases as the amount of the Fe content increases [4]. The bandgap is 1.5eV. Dielectric Studies The dielectric constant and dielectric loss of pure and CuO pellet were studied using a HIOKI 3532 LCR meter as a function of frequency (50 Hz – 100 kHz) at room temperature. Dielectric Constant: Ɛ’= Cpd/Ɛ0A Where, Cp is the capacitance, Ɛ0 is the permittivity of free space (8.854 X 10-12F/m), A is the area of the space, d is the thickness of the pellet. Fig 6.a shows that the frequency dependence on Ɛ’, decreases with increase in frequency. This type of behaviour is explained on the basis of different polarization (electronic, ionic, dipolar, and space change) mechanisms at different frequency ranges.
Proceedings of National Laser Symposium (NLS-22), Manipal University, Manipal. 8-11 Jan 2014 Dielectric Loss: The dielectric loss Ɛ” of the material is calculated by the relation ɛ” =
x loss. Dielectric loss
represents the energy dissipation in dielectric systems. Fig 6.b shows the variation in dielectric losses factor with frequency at room temperature. It is observed that Ɛ’ decrease with increase in frequency for CuO which is due to the space charge polarization [5]. .
Fig 6 a) variation of the dielectric constant b) dielectric loss for pure CuO
Conclusion The present study demonstrates the synthesis of undoped and Fe doped CuO nanoparticles by sol-gel method. X-ray diffraction pattern confirms the formation of pure CuO monoclinic single phase. The crystallite size varies in the ranges. SEM analysis shows agglomeration of CuO nanoparticles. From the EDAX spectrum confirms the presence Fe. The optical bandgap of CuO decreases from 1.5eV to 1.0eV with increasing Fe doping levels. Room temperature FL spectra reveal the presence of Fe defects. The dielectric constant and loss decreases with an increasing frequency. References 1.
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N. Mohamed Basith, J.JudithVijaya, L.JohnKennedy, M.Bououdina. Physica E 53 193-199 (2013).
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