Structural, optical and magnetic properties of undoped NiO and Fe-doped NiO nanoparticles synthesized by wet-chemical process

    Structural, optical and magnetic properties of undoped NiO and Fe-doped NiO nanoparticles synthesized by wet-chemical process P.M. Ponnusamy, S. Agilan, N. Muthukumarasamy, T.S. Senthil, G. Rajesh, M.R. Venkatraman, Dhayalan Velauthapillai PII: DOI: Reference:

S1044-5803(16)30045-6 doi: 10.1016/j.matchar.2016.02.020 MTL 8190

To appear in:

Materials Characterization

Received date: Revised date: Accepted date:

28 October 2015 23 February 2016 29 February 2016

Please cite this article as: Ponnusamy PM, Agilan S, Muthukumarasamy N, Senthil TS, Rajesh G, Venkatraman MR, Velauthapillai Dhayalan, Structural, optical and magnetic properties of undoped NiO and Fe-doped NiO nanoparticles synthesized by wet-chemical process, Materials Characterization (2016), doi: 10.1016/j.matchar.2016.02.020

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ACCEPTED MANUSCRIPT Structural, optical and magnetic properties of undoped NiO and

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Fe-doped NiO nanoparticles synthesized by wet-chemical process

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P.M.Ponnusamya*, S.Agilana, N.Muthukumarasamya, T.S.Senthilb,

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Department of Physics, Coimbatore Institute of Technology, Coimbatore, India. b

Department of Physics, Erode Sengunthar Engineering College, Erode, India.

c

Department of Engineering, University College of Bergen, Bergen, Norway.

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a

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G.Rajesha, M.R.Venkatramana, Dhayalan Velauthapillaic

nickel oxide (NiO) and ferrous doped NiO

dilute magnetic

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Nanocrystalline

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Abstract

nanoparticles have been prepared by wet-chemical method. The structural, composition,

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morphology, UV absorption and magnetic analysis of the prepared samples are characterized by XRD, FESEM, HRTEM, UV Spectra

and VSM.

XRD confirms the FCC

phase

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formation. The FESEM and HRTEM used to found the structural parameters. The U-V absorption measurement shows the strong absorption at 313.24 nm undoped

NiO and

and 307.9 nm for

Fe-doped NiO nanoparticles. The magnetic properties of

these

nanoparticles confirming the ferromagnetic behaviour at room temperature and has been attributed due to particle size effect.

Key words: Nanoparticles, Fe-doped NiO, wet-chemical method, Ferro magnet. Corresponding author

: +91-9942586302(P.M.Ponnusamy),

E-mail

: [email protected]

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Introduction

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Nanostructured materials have attracted great interest due to its outstanding physical

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and chemical properties and also promising applications in nanodevices[1]. Nanocrystalline nickel oxide is an important transistion metal oxide and used in variety of applications like smart

windows, electrochemical

super capacitors and also in dye sensitized photo

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Cathode[2-8].

Among the metal oxides, NiO nanoparticles is a P-type semiconductor with wide

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band gap in the range of 3.6 eV to 4.0 eV[9]. Nanocrystalline NiO also possesses interesting magnetic properties related to size and surface effects[10,11]. Magnetism of nanomaterials

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has become a significant concern in nanoscience due to the expected spectacular properties

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for its wide applications in diverse fields such as high density recording media, spin valves,

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magnetic resonance imaging, ferrofluid technology and magnetocaloric refrigeration [12,13]. Diluted magnetic semiconductor (DMS) is a kind of novel semi- conductors, which is formed using magnetic transition metal ions or rare earth metal ions to randomly replace the non-

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magnetic cations in semiconductors and to make the semiconductor show magnetic properties [14]. Such semiconductors are potential candidates for applications of spincontrolled devices. The doping of transistion metal ions into NiO lattice modifies electronic and magnetic properties. Dilute magnetic systems have attracted much attention because of complex spin order[15]. The magnetic and structural properties changes significantly with Fe doping. The antiferromagnetic behavior of NiO can be tuned by replacing Ni by transition metal ions(Fe3+) and shift to ferromagnetic behaviour[16]. Wang et al (2005) reported that Fe-doped NiO nanoparticles reveal room temperature ferromagnetism[17].

Manna et

al(2009) reported that size reduction in transition metal ions to NiO nanoparticles plays an important role in ferromagnetic phase due to an uncompensated spin sublattice[18]. Mishra et al(2009) reported that the presence of dopent concenteration level below 3% shows trace amount of magnetic changes occur and phase changes could not detected by XRD[19]. NiO

ACCEPTED MANUSCRIPT nanoaparticles have been prepared by different researchers using various methods such as sol-gel method[20], solvothermal method[21], hydrothermal method[22], chemical method[23], sonochemical method[24], anodic plasma technique[25], microemulson

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method[26], and thermal decomposition method[27]. The wet-chemical precipitation is

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extensively studied as a effective method to produce metal oxide nanoparticles because it gives a higher specific surface area, superior homogeneity and purity, better micro structural

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control of metallic particles, narrow pore size and uniform particle distribution. In addition, the wet-chemical precipitation method also offers several other advantages, like low temperature processing, possibility of high yield

and most importantly cost effective. as it permits

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Chemical precipitation method is more suitable to prepare nanoparticles

molecular-level mixing and processing of the raw materials and precursors at relatively lower

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temperature and produces nano-structured bulk, powder and thin films. Synthesis of NiO nanoparticles is a typical process and preparation conditions may affect the property of nanoparticles. For improving the property of nanoparticles, wet-chemical process has been

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used and the particle size can be easily controlled by this method. There are some

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parameters such as particle size, morphology, composition purity and crystallinity which determines the optical and magnetic properties of nanoparticles. In the present work pure

Experimental

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and Fe-doped NiO particles structural, optical and magnetic property has been discussed.

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Undoped NiO and Fe-doped NiO nanoparticles have been prepared by wet-chemical process following the modified procedure of Menese et al(2007)[28]. For preparing NiO nanoparticles, 100 mL of 0.1M

nickel nitrate[Ni(NO3).6H2O] aqueous solution was

prepared and then 100mL of 0.1M NaOH was added drop wise to the above solution. The mixture was stirred for 2 hours at room temperature to complete the reaction and for the formation of precipitate. Finally the precipitate was centrifuged at 3000 rpm for 5 minutes and washed with distilled water several times to remove Na ions. The collected precipitate was allowed to dried for 12 hours and annealed at 350ºC for 2 hours. The dried powder was grinded to get undoped NiO nanoparticles.

ACCEPTED MANUSCRIPT For preparing Fe-doped NiO nanaoparticles, 0.202g of ferric nitrate (Fe(NO3).9H2O) and 2.7625g of nickel nitrate was added to 100 mL of double distilled water and stirred for 1 hour at room temperatur to get mixture of 0.1M nickel nitrate and ferric nitrate

solution.

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Then the aqueous solution of 0.1M NaOH was added drop wise to the above mixture and

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stirred it for 2 hours and also maintain the pH~ 13 . Following the above procedure and to get 5% Fe-doped NiO particles. Annealing temperatute, stirring time and precursor

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concentration are the key parameters to alter the nanoparticle size.

studies

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To identify the structure and phase purity of the prepared samples, X-ray diffraction was carried out using a X-ray diffractometer (XPERT-PRO PW3050) at room

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temperature. The surface morphology was studied using field emission scanning electron microscope (FESEM, Zeiss supra 55VP). The energy dispersive X-ray analysis (EDAX) and

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high resolution transmission electron microscope (HRTEM) images of the prepared samples

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have been recorded using a JEOL JEM-2100F. The UV-visible absorbance spectra was recorded by using spectrophotometer (JASCO V-570) in the range of 200-800nm to

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determine the band gap of the prepared samples. Magnetization measurement (M-H characterisation) of the samples was carried out using vibrating sample magnetometer (Lake

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Shore: Model: 7404).

Result and Discussion The X-ray diffraction patterns of the undoped NiO and Fe-doped NiO nanoparticles are shown in Fig.1&2. The diffraction peaks at 2θ are 37.2, 43.3, 62.7, 75.6 and 79.4 then indexed as (111), (200), (220), (311) and (222) planes of NiO(Fig.1). The lattice constants have been found to be a = 4.174 Å and are in agreement with the standard data [JCPDS Card No: 01-078-0423] corresponds to FCC structure of NiO nanoparticles. The result clearly shows that the synthesised undoped NiO nanoparticles had high purity with the absence of impurity peaks. Also it is observed that the diffraction peaks of Fe-doped NiO shows a small shift towards higher 2θ values when compared to that of undoped NiO. This shift may be due to the occupation of Fe3+ ions(r =0.74Ǻ ) at the Ni2+ sites(r =0.69Ǻ). The lattice

ACCEPTED MANUSCRIPT constants of Fe-doped NiO nanoparticles was

a = 4.164 Å, which are smaller than those

of undoped NiO. The diffraction pattern reveals that undoped NiO and Fe-doped NiO nanoparticles exhibit FCC structure. No characteristic peaks of impurity phases are observed

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in the X-ray diffraction patterns of the doped samples. The intensity of all the diffraction

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peaks have substantially decreased and broading of peaks increase on Fe doping which indicates that the crystallization of the Fe-doped NiO nanoparticles had deteriorated

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(Fig.2). The incorporation of Fe ions into NiO creates internal micro strain and microstructural disorder in the NiO lattice which affects the grain growth and broadens the Bragg’s peak (Granqvist, 1995). Hence the intensity reduction take place.The reduced grain

of undoped NiO and Fe-doped NiO nanoparticles

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The grain size

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size indicates that the growth of host lattice was restricted by Fe3+ ions.

has been

estimated by using the Scherer relation[29] ,

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(1)

where D is the grain size, K is a constant taken to be 0.94, λ is the wave length of X-rays,

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β is the full width at half maximum intensity and θ is the Bragg’s angle(angle of diffraction). The grain size has been calculated and is found to be 11.97 nm, and 8.11 nm for undoped respectively. The Fe-doped NiO nanoparticles

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NiO and Fe-doped NiO nanoparticles

exhibited smaller grain size than undoped NiO nanoparticles (Moura et al 2012)[16] and this can be attributed to the fact that Fe3+ ion increases the nucleus number when it incorporates into the NiO nanoparticles (Cheong et al 2002)[30]. Similar results have been noticed in Indoped (Caglar et al 2009)[31] and Al-doped ZnO films (Ratana et al 2009)[32]

Fig.3 shows the FESEM images of undoped NiO and Fe-dopedNiO nanoparticles. It is observed that grains are small and are uniformly distributed throughout the surface. The images of undoped NiO nanoparticles shows the agglomeration of the particles. The agglomeration occurs due to the nano dimension of the crystal size and small nanocrystal

ACCEPTED MANUSCRIPT posses large surface energy. The images of Fe-doped NiO shows that the particles size is nearly uniform. The introduction of Fe ions into NiO reduces the grain size which indicates

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the increase of strain in the matrix and restricts the lattice growth(Moura et al, 2012)[16].

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The surface morphology of the sample prepared using lower concentration of nickel nitrate is smooth due to higher the surface energy. At higher concentration agglomeration of particles

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results in the reduction of surface smoothness and surface energy. Similar results has been reported by Ayeshamariam et al (2013)[33 ]. As Annealing temperature increases the particle agglomeration results in the increase of particle size. The doping produces a change in the

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sample micro structure and a more disperse system is obtained.

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Fig.4 shows the HRTEM images of undoped NiO and Fe-doped NiO nanoparticles. The image shows that the undoped NiO nanoparticles are nearly spherical in nature with

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little agglomeration and a change in morphology is found with insertion of Fe3+ ions in the

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host NiO matrix(Mishra et al 2012 )[19]. The estimated grain size calculated from HRTEM images are in good agreement with XRD results(Table 1). The HRTEM images (fig.5) shows

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fringe pattern and the d-spacing have been found from the fringe pattern. The d-spacing values calculated from the fringe pattern are 2.088 Å, and 2.083 Å for undoped NiO and Fe-

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doped NiO nanoparticles which correspond to the (200) plane of face centred cubic NiO. The decrease in d-spacing of Fe-doped NiO due to the difference of ionic radii . The selected area electron diffraction(SAED) pattern of undoped NiO and Fe-doped NiO

are

shown in fig.6. The observed rings of Fe-doped NiO are identified as that of undoped NiO, which confirms crystalline nature and phase purity of the prepared samples. Fig.7 shows the energy dispersive X-ray analysis (EDAX) of undoped NiO and Fe-doped NiO nanoparticles. EDAX spectrum of NiO nanoparticles have peaks corresponds to Ni and O. The components C and Cu present in the figure originates from the paste and grid used for EDAX analysis. The EDAX analysis exhibited clear peaks of Ni and O elements only, whereas no additional peaks were detected, which means that the as prepared powder has no

ACCEPTED MANUSCRIPT impurities. For Fe-doped NiO sample, Fe peak conforms the proper doping of Fe in the NiO matrix.

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Fig.8 shows the optical absorption spectra of undoped NiO and Fe-doped

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NiO nanoparticles respectively. The absorption edge of undoped NiO nanoparticles was

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found to be at 313.24 nm and Fe-doped NiO was found to be at 307.9 nm. The absorption spectra of Fe-doped NiO nanoparticles shows that the absorption edge is slightly shifted towards shorter wavelength (blue shift) when compared to undoped NiO. This shift is due to

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the Burstein–Moss effect, since the absorption edge of a degenerate semiconductor is shifted

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to shorter wavelengths with increasing carrier concentration (Burstein, 1954). This shift towards blue region predicts that there is an increase in band gap value(Eg), which is due to

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the reduction in particle size. The fundamental absorption, which corresponds to the electron

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transistion from the valance band to the conduction band, can be used to determine the nature and value of the optical band gap. The optical absorption study was used to determine

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the optical band gap of the nanoparticles, which is the most familiar and simplest method. The fundamental absorption, which corresponds to the electron transistion from the valance

band gap.

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band to the conduction band, can be used to determine the nature and value of the optical

The absorption coefficient (α) and the incident photon energy (hʋ ) are related by the expression[34]. (αhʋ ) = A(hʋ -Eg)n

(2)

where A is a constant relative to materials, Eg is the optical band gap of the material, ʋ is the frequency of the incident radiation, h is the Planck’s constant and exponent n is 0.5 for direct band allowed transition. The optical band gap of the undoped NiO nanoparticles and Fe-doped NiO nanoparticles have been determined using the equation 2. Fig.9 shows the (αhʋ ) 2 versus hʋ plot of undoped NiO and Fe-doped NiO nanoparticles. The optical band

ACCEPTED MANUSCRIPT gap values have been determined by extrapolating the linear portion of the the curve to meet the energy axis(hʋ ). The band gap has been calculated and is found to be 3.958eV and

is higher

than that of undoped

NiO due to quantum

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Fe-doped NiO nanoparticles

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4.026eV for undoped NiO and Fe-doped NiO respectively. The obtained optical band gap of

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confinement effect [35].

The magnetic properties of as prepared samples were performed by magnetic hysteresis

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loop at room temperature. Fig.10 shows the appearance of a hysteresis curve for undoped

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NiO indicates the presence of week ferromagnetic phase and it is increased for Fe-doped samples(Fig.11). The same result which absorbrd by Moura et al (2010)[16]. Doping effect Doping of Fe into NiO

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reduces the particle size and enhances the net magnetization.

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interface creates charge carriers which gives more exchange interaction . The saturation magnetization is 115.54E-6 emu/g for undoped NiO and 1.9E-3 emu/g for Fe-doped NiO.

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The hysteresis phenomenon for Fe-doped NiO is coincide with earlier result reported by Lin et al (2006)[36] and the curve is slowly narrow due to uncompensated spins systems (Manna

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et al 2009)[18]. The magnetic properties of the materials have been closely associated with the dependence of particle size, shape, magnetic direction and crystallinity.

Conclusion Undoped NiO and Fe-doped NiO dilute magnetic

nanoparticles

have been

successfully synthesized by wet-chemical method. The XRD study confirms the formation of NiO and Fe-doped NiO nanoparticles and also indicated the FCC phase formation. The grain size (8.11 nm) of Fe-doped NiO nanoparticles is smaller than the grain size (11.97 nm) of undoped

NiO nanoparticles. The grain size of undoped NiO and Fe-doped NiO

are

calculated from Scherrer’s equation agrees well with HRTEM result. The UV absorption

ACCEPTED MANUSCRIPT spectra of Fe-doped NiO nanoparticles is found to be shift towards the lower wavelength side when compared to that of undoped NiO nanoparticles. The M-H curves shows the week

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ferromagnetic phase for undoped NiO and increased for Fe-doped NiO.

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ACCEPTED MANUSCRIPT Figure.1

XRD pattern of undoped NiO nanoparticles

Figure.2 XRD pattern of Fe-doped NiO nanoparticles FESEM images of a) Undoped NiO nanoparticles and b) Fe-doped NiO

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Figure.3

HR-TEM image of (a) Undoped NiO nanoparticles and b) Fe-doped NiO

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Figure.4

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nanoparticles

nanoparticles

HR-TEM image fringe pattern of of (a) Undoped NiO nanoparticles and

b) Fe-doped NiOnanoparticles

SAED Pattern of (a) Undoped NiO nanoparticles and b) Fe-doped NiO

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Figure.6

nanoparticles

EDS spectrum of (a) Undoped NiO nanoparticles and b) Fe-doped

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NiOnanoparticles

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Figure.7

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Figure.5

Figure.8 Absorbance spectra of (a) Undoped NiO nanoparticles and

Figure.9

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(b) Fe-doped NiO nanoparticles Plot of (h)2 vs. photon energy of (a) Undoped NiO nanoparticles

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and (b) Fe-doped NiO nanoparticles Figure.10

Hysteresis curves of undoped NiO nanoparticles

Figure.11 Hysteresis curves of Fe-doped NiO nanoparticles

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Table 1

H RTEM Å

2.08

2

7

Fedoped NiO

.088 2.08

2

.083

TE CE P AC

H RTEM n m

XRD Pattern Å

H RTEM Å

11.9

1

4.17

4

7

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2

XRD Pattern nm

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XRD Pattern Å

Undop ed NiO

Lattice constant “a”

Grain size

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Sampl es

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Calculated ‘d-spacing’ values

8.11

1.78

4 8

.23

.176 4.16

4

4 .166

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nanoparticles

have been

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 Undoped NiO and Fe-doped NiO dilute magnetic successfully synthesized by wet-chemical method.

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Highlights

 The XRD study confirms the formation of NiO and Fe-doped NiO nanoparticles and also indicated the FCC phase formation.

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 The UV absorption spectra of Fe-doped NiO nanoparticles is found to be shift towards the lower wavelength side when compared to that of undoped NiO nanoparticles.

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 The M-H curves shows the week ferromagnetic phase for undoped NiO and increased for Fe-doped NiO