Structural, optical and magnetic properties of Co doped CuO nano-particles by sol-gel auto combustion technique

Solid State Sciences 95 (2019) 105936

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Structural, optical and magnetic properties of Co doped CuO nano-particles by sol-gel auto combustion technique

T

S.P. Kamblea,*, V.D. Moteb a b

Department of Physics, Chandmal Tarachand Bora College of Arts, Commerce and Science, Shirur, 412 210, Maharashtra, India Thin Films and Materials Science Research Laboratory, Department of Physics, Dayanand Science College, Latur, 413 512, Maharashtra, India

ARTICLE INFO

ABSTRACT

Keywords: CuO Nanoparticles X-ray diffraction Strain Monoclinic Superparamagnetism

Co-doped CuO nanoparticles were successfully prepared by sol-gel auto combustion technique to investigate structural, optical and magnetic properties. The X-ray diffraction (XRD) analysis studied the structural properties of the nanoparticles and confirms structure of the monoclinic CuO crystal structure. As the Co doping increases the volume of unit cell decrease in Co doped CuO nanoparticles. The mean crystalline size was determined using Scherrer's formula and found in the range of 35–40 nm. The effects of Co doping on the variation of the microstrucutre property in the Co doped CuO nanoparticles were revealed by scanning electron microscope (SEM). The EDX analysis showed that the atomic percentage of Cu decreases with the increasing doping (Co) concentrations, which have confirms that the Cu atoms have successfully replaced their Co counterparts as content. The optical data revealed that with an increase in Co doping level there is an energy band gap increase. The magnetic hysteresis loops of the samples indicated that the samples are super-paramagnetic in nature. The super-paramagnetic behavior of the samples is also discussed.

1. Introduction

magnetic oxides is still in debate [11–13]. CuO nanoparticles disclose strong size dependent magnetic properties i.e. weak ferromagnetism and superparamagnetism [14,15]. The formation of Cu1-xCoxO nanoparticles have reported with different methods such as the sonochemical method [16], sol–gel technique [17] one-step solid state reaction method at room temperature [18] electrochemical method [19] thermal decomposition of precursors [20] and high-temperature combustion [21] etc. Among these techniques, sol-gel auto combustion technique offers simple, cost effective by using cheaper chemical and industrially scalable route for the production of high quality nanoparticles. In this paper, we report the preparation and characteristics of pure and Co doped CuO nanoparticles. Systematic investigation of structural, morphological and magnetic properties of Co doped CuO nanoparticles and optical properties have been also studied. We have observed that pure and Co-doped CuO nanoparticles show superparamagnetism behavior at room temperature by sol-gel auto combustion method.

Oxide based dilute magnetic semiconductor nanoparticles (DMS) have promising materials for next generation spintronics devices due to the possibility of seamlessly integrating DMS into current semiconductor technology [1]. The important property of DMS is the room temperature ferromagnetism can be drawn. Recently, DMS oxides nanoparticles such as ZnO, SnO2, CuO and TiO2, which is no common conclusion about the magnetism for CuO samples doped with FM and synthesized by various techniques [2–6]. Recently, CuO nanoparticles have attracted have been of the wide applications such as catalysis, semiconductor devices, semiconductor and biomedical. In addition, CuO nanoparticles have unique properties i.e. super-paramagnetic and increasing susceptibility at low temperature. Hence it is meaningful to investigate optical and magnetic measurement of CuO nanoparticles. CuO has a monoclinic structure with an direct band gap of 1.2 eV [7]. The CuO have potential applications in solar cells, catalysis and optics [8,9]. All these properties remarkable doped CuO a promising material that many combine the optical, transport and optical properties for devices. There are limited works to develop oxide based DMS nanoparticles on CuO [10]. The origin room temperature ferromagnetism of nanoscale metal oxides and diluted *

2. Experimental details The sample of cobalt doped copper oxide nanoparticles were prepared by sol-gel auto combustion method. Cupric acetate

Corresponding author. E-mail address: [email protected] (S.P. Kamble).

https://doi.org/10.1016/j.solidstatesciences.2019.105936 Received 20 May 2019; Received in revised form 12 July 2019; Accepted 14 July 2019 Available online 15 July 2019 1293-2558/ © 2019 Elsevier Masson SAS. All rights reserved.

Solid State Sciences 95 (2019) 105936

S.P. Kamble and V.D. Mote

(311) and (004) planes (as shown in Fig. 1) which is good agreement with the JCPDS data Card no. 80–1916. The XRD patterns showed that the nanoparticles were polycrystalline in nature with a monoclinic CuO crystal structure. As the Co doping increased, there is no change the crystal structure significantly. The lattice parameters were determined using the following equation:

d=

( )+( ) ( h2 a2

l2 c2

2hl ac

sin2

cos

)+k

2

1 2

b2

(1)

where θ is diffraction angle, d is the interspacing distance, λ is incident wavelength (λ = 0.15406 nm) and h, k, l are the Miller indices. The values of lattice parameters are given in Table 1. The lattice parameters ‘a’, ‘b’ and ‘c’ decreased with increasing Co doping due to the small difference between the Co2+ ion (0.72 Å) and Cu2+ ion (0.73 Å). As the Co doping content increases the value of volume of unit cell is decreased. The significant change in the values of lattice parameters and volume with Co doping, it means that Co2+ ions are substituted with Cu2+ ions which are in CuO structure; similar result obtained by Ponnarasan et al. [22]. Scherrer's formula was used to determine the crystallite size of Co doped CuO nanoparticles from the XRD patterns (see Table 2). Scherrer's formula is given as follows:

Fig. 1. XRD patterns of the pure and Co doped CuO nanoparticles.

[(CH3COO)2Cu•H2O], Cobalt Acetate [(CH3COO)2Co•4H2O], citric acid (C6H8O7) and ionized distilled water was used. The 1 M cupric acetate was dissolved in 100 ml distilled water and 1 M Cobalt Acetate was dissolved in 100 ml distilled water and 1 M citric acid was dissolved in 100 ml distilled water stirring for 30 min at room temperature. The solution of Cobalt Acetate added drop wise cupric acetate and stirrer it for 30 min at room temperature. The citric acid solution drop wise added in the mixed solution and stirred at 100 °C nearly 3 h. The gel was formed and after 20 min the auto combustion process was take place and we got dark black powder. Then this obtained powder grinded for 25 min and sintering at 200 °C in furnace for 1 h. The crystalline structure, phase purity and size of the pure and Co doped CuO nanoparticles were determined by X-ray diffraction (XRD) using X-ray diffractometer (Model: PW-3710) employing Cukα (λ = 1.5406 Å) radiation, operating at 40 kV and 40 mA, in the 2θ range 20-800 with a scanning step of 0.020. To study the sample morphology, the powders were ultrasonically mixed with ethanol and suspended on a Cu mesh, which is the sample holder of scanning electron microscope (SEM) operated at 200 kV(SEM- Model CM 200, SUPERTWIN). Absorption spectra were recorded using UV–Vis spectrometer (JASCO) in the wavelength range 200–800 nm with a step of 2 nm. A magnetic property was study using vibrating sample magnetometer (VSM) at room temperature.

D=

0.9 cos

(2)

where D is the crystalline size, λ is the wavelength of Cu-Kα irradiation (1.54006 Å), β is the full width half maxima (FWHM), θ is the Bragg's diffraction angle, and K is the shape factor (0.89). The calculated crystalline size for pure and Co doped CuO nanoparticles are given Table 1. The crystalline size was decreased with increasing Co doping. As the Co doping concentration increased, the strain decreased from 1.05 Χ10−3 to 1.03 Χ10−3. This show that the decrease in lattice imperfections and formation of high-quality nanoparticles. 3.2. Morphological study The SEM images of pure, 5% and 10% Co doped CuO nanoparticles are shown in Fig. 2(a) and (b) and 2(c) respectively. The SEM images of samples in different concatenation of Co doping show similar behaviors, confirming the uniformality and polycrystalline nature of the nanoparticles. The undoped and Co doped CuO nanocrystalline particles showed spherical like structured particles. However, the doping concentration of Co affected the appeared of the surface morphology for all samples. The EDX analysis was done and the result is shown in Fig. 3. In EDX spectrum, numerous well-define peaks were evident concerned to Cu, O, and Co which clearly support that the Co doped CuO nanoparticles are made of Cu, O, and Co. No other peaks related to impurities were detected in the spectrum, which further confirms that the synthesized particles are Co doped CuO nanoparticles. The EDX analysis also

3. Results and discussion 3.1. Structural study Fig. 1 shows the XRD patterns of pure and Co doped CuO nanoparticles annealed at 200 °C. The intensive peaks corresponds to the (110), (002), (−111), (−202), (020), (202), (−113), (110), (−311), Table 1 Structural parameters, crystalline size and strain of Co doped CuO nanoparticles. Samples

Pure CuO 05% Co 10% Co

Lattice parameters (Å) a (Å)

b (Å)

c (Å)

4.6614 4.6586 4.6190

3.4321 3.4231 3.4151

5.1294 5.1207 5.1014

2

Volume of unit cell V(Å)3

Crystallite size D (nm)

Strain ε (Dimensionless)

80.9567 80.5584 79.3863

39.67 35.67 34.93

0.00105 0.00103 0.00102

Solid State Sciences 95 (2019) 105936

S.P. Kamble and V.D. Mote

Table 2 Corecivity, saturation magnetization and retentivity of Cu1-xCoxO nanoparticles. Samples

Corecivity (Hc) Oe

Saturation Magnetization (Ms) emu/gm

Retained Magnetization (Mr) emu/gm

Pure CuO 5% Co 10% Co

174.5062 77.4691 30.7407

30.9325 30.4619 31.6720

0.4068 0.5336 1.9826

Fig. 2. SEM images of the pure and Co doped CuO nanoparticles.

Fig. 3. EDX analysis of the pure and Co doped CuO nanoparticles.

showed that the atomic percentage of Cu decreases with the increasing doping (Co) concentrations, which have confirms that the Cu atoms have successfully replaced their Co counterparts as content.

the following equation:

hv = A(hv

Eg) m

(3)

where α is an energy-independent constant, hν is the photon incident energy, m is a constant that determines the type of optical transition; for an indirect allowed transition, m = 2, for an indirect allowed transition, m = 3; and for a direct forbidden transition, m = ½. The Tauc plot of pure and Cu1-xCoxO samples are shown in Fig. 5(a) and (b). The band gap energy values for the nanoparticles changed from 1.64 eV, 1.73 eV and 1.70 eV with 0%, 5% and 10% Co doping, respectively. This band gap changes due to the quantum size effect. The

3.3. Optical study The optical absorption spectra of Cu1-xCoxO nanoparticles are shown in Fig. 4. To investigate the effect of Co doping concentration on the optical properties, the band gap and absorption of each nanoparticle were study in the range of 200–800 nm. The optical band gap energies were evaluated using Tauc plot, by

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Solid State Sciences 95 (2019) 105936

S.P. Kamble and V.D. Mote

bang gap energy was 1.73 eV for Co doped CuO of 5% Co doping. Hardee et al. [23]. reported that the semiconducting properties, CuO exhibit p-type conductivity with a band gap of 1.2–1.8 eV. 3.4. Magnetic study Hysteresis loops have been observed for pure, 5% and 10% Co doped CuO nanoparticles by vibrating sample magnetometer at room temperature and as shown in Fig. 6. No ferromagnetism is observed for all prepared samples. Pure and Co doped CuO samples show the superparamagnetism nature. In our case, the pure CuO have the superparamagnetism behavior due to the average crystallite size d = 39.67 nm. The magnetic measurement confirms that the superparamagnetism and enhanced magnetic moments are caused by the existence of uncompensated surface spins of the CuO nanoparticles by Rao et al. [24]. Yin et al. [25]. studied that the magnetic properties of particles are seen to evolve from PM to FM behaviors with increasing grain size and magnetization saturates nearly for the particles size of 50 nm as the applied field is 10 kOe for Fe doped CuO nanoparticles. Similar results was obtained i.e. Co doped CuO nanoparticles have superparamagnetism at room temperature. In addition, superparamagnetism appears generally in Ferro or ferromagnetic nanoparticles of size around 03–50 nm. The Co is FM in nature, when it combines with CuO and reduced to nano-region at room temperature, there is a decrease in magnetization and exhibits superparamagnetism behaviors [26]. Lin et al. [27]. reported that the corecivity remains nonzero (~130 Oe) even at room temperature, revealing that the Fe doped CuO sample is still ferromagnetic at 300 K. The saturation magnetization (Ms), coercive field (Hc) and retentivity (Mr) are calculated using the hysteresis loops and given Table 1. The coercive field decrease with increasing Co doping whereas the retentivity increased. The saturation magnetization of pure and Co doped CuO nanoparticles were found in the range of 30–33 emu/gm.

Fig. 4. Absorption spectra of the Cu1-xCoxO nanoparticles.

4. Conclusion To conclude, Cu1-xCoxO nanoparticles of different doping concentration such as 5% and 10% Co were synthesized co-precipitation method. The X-ray diffraction analysis confirms that all prepared nanoparticles have monoclinic CuO crystal structure. As Co doping concentration increases, the lattice parameters and volume of unit cell were decreased indicating the Co incorporation in CuO host matrix. The average crystallite prepared samples was in the range of 35–40 nm. Morphological analysis done by SEM images reveal that spherical in shape slightly agglomerated spherical nanoparticles. From the EDX data, it reveals that the atomic percentage of Co increases in CuO samples. This shows that Co atoms have been successfully substituting in CuO samples. Optical spectroscopic measurements indicate that Co doping is affected on absorption edge of CuO nanoparticles. Cu1-xCoxO nanoparticles behave as superparamagnetism nature at room temperature. Based on this study, prepared pure and Co doped CuO nanoparticles are suitable for solar cell, spintronics and nano-device applications. Acknowledgements: Authors are grateful to Principal, C.T. Bora College Art, Commerce and Science, Shirur Dist. Pune, MS India, for giving permission to carry out this study and to provide research facility. S.P. Kamble is thankful to the University Research Grants Scheme, BCUD, Savitribai Phule Pune University, Pune, MS India, for the award of the research project Proposal no. 15SCI000551 for this study Fig. 5. (a). Tauc plot of the pure and 5% Co doped CuO nanoparticles. (b). Tauc plot of the 10% Co doped CuO nanoparticles.

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Solid State Sciences 95 (2019) 105936

S.P. Kamble and V.D. Mote

Fig. 6. Magnetization as a function of the magnetic field for Cu1-xCoxO nanoparticles.

Acknowledgements

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Authors are grateful to Principal, C.T. Bora College Art, Commerce and Science, Shirur Dist. Pune, MS India, for giving permission to carry out this study and to provide research facility. S.P. Kamble is thankful to the University Research Grants Scheme, BCUD, Savitribai Phule Pune University, Pune, MS India, for the award of the research project Proposal no. 15SCI000551 for this study Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.solidstatesciences.2019.105936. References [1] H. Ohno, D. Chiba, F. Matsukura, T. Omiya, E. Abe, T. Dietl, Y. Ohno, K. Ohtani, Nature (London) 408 (2000) 944. [2] T. Fukumura, H. Toyosaki, Y. Yamada, Semicond. Sci. Technol. 20 (2005) S103. [3] R. Janisch, P. Gopal, N.A. Spaldin, J. Phys. Condens. Matter 17 (2005) R657. [4] T. Fukumura, Z.W. Jin, M. Kawasaki, T. Shono, T. Hasegawa, S. Koshihara, H. Koinuma, Appl. Phys. Lett. 78 (2001) 958. [5] S.B. Ogale, et al., Phys. Rev. Lett. 91 (2003) 077205. [6] J. M. D. Coey, A. P. Douvalis, C. B. Fitzgerald, and M. Venkatesan, Appl. Phys. Lett. 84, 1332 (200). [7] H. Zhu, F. Zhao, L. Pan, Y. Zhang, C. Fan, Y. Zhang, J.Q. Xiao, J. Appl. Phys. 101

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