Synthesis, characterization and study of magnetic, electrical and dielectric properties of La1−xDyxCo1−yFeyO3 nanoparticles prepared by wet chemical route

Author’s Accepted Manuscript Synthesis, characterization and study of magnetic, electrical and dielectric properties of La1−xDyxCo1−yFeyO3 nanoparticles prepared by wet chemical route Qurshia Choudhry, Muhammad Azhar Khan, Gulfam Nasar, Azhar Mahmood, Muhammad Shahid, Imran Shakir, Muhammad Farooq Warsi

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S0304-8853(15)30167-0 http://dx.doi.org/10.1016/j.jmmm.2015.05.040 MAGMA60216

To appear in: Journal of Magnetism and Magnetic Materials Received date: 12 March 2015 Revised date: 8 May 2015 Accepted date: 17 May 2015 Cite this article as: Qurshia Choudhry, Muhammad Azhar Khan, Gulfam Nasar, Azhar Mahmood, Muhammad Shahid, Imran Shakir and Muhammad Farooq Warsi, Synthesis, characterization and study of magnetic, electrical and dielectric properties of La1−xDyxCo1−yFeyO3 nanoparticles prepared by wet chemical r o u t e , Journal of Magnetism and Magnetic Materials, http://dx.doi.org/10.1016/j.jmmm.2015.05.040 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Synthesis, characterization and study of magnetic, electrical and dielectric properties of La1-xDyxCo1-yFeyO3 nanoparticles prepared by wet chemical route

Qurshia Choudhrya, Muhammad Azhar Khanb, Gulfam Nasara, Azhar Mahmooda, Muhammad Shahida, Imran Shakirc, Muhammad Farooq Warsi*a a

Department of Chemistry, The Islamia University of Bahawalpur, Bahawalpur-63100, Pakistan

b

Department of Physics, The Islamia University of Bahawalpur, Bahawalpur-63100, Pakistan

c

Department of Chemistry, University of Agriculture, Faisalabad , Pakistan

d

Deanship of scientific research, College of Engineering, PO Box 800, King Saud University, Riyadh 11421, Saudi Arabia Corresponding author: [email protected], Phone: +92 345 5411391

Abstract Dy3+ and Fe3+ co-doped LaCoO3 perovskite nanoparticles were prepared by chemical coprecipitation route. Structural elucidation was carried out by thermo gravimetric analysis (TGA), X-ray diffraction (XRD), Scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) spectroscopy. The data of all these characterization techniques confirmed the orthorhombic phase with particles size in the range of 20-60 nm. The magnetic parameters, DC-resistivity and dielectric properties were measured for La1-xDyxCo1-yFeyO3 nanoparticles. The purpose of all these application studies was to evaluate the prepared materials for practical applications. The substitution of Dy3+ and Fe3+ with La3+ and Co3+ respectively greatly influenced the magnetic, DC-resistivity and dielectric parameters. Key Words: Rare earth; Nanoparticles; Electrical resistivity; Dielectric properties; Magnetic parameters; Microwave devices.

1. Introduction Nanoscience and nanotechnology is a new emerging field that has already attracted the researchers and engineers. Nanomaterials can be prepared by taking the metal, non-metals, polymeric materials etc. However the transition metals and the rare-earth elements have rich chemistry due to the inherent variable oxidation states. The application spectrum of both Lanthanide and metal oxide nanomaterials can further be broadened by controlling their size in the nano-regime range [1]. Perovskites, the metal oxides with general formula ABO3, are very technologically very important because of their versatile applications [2]. The structural and other parameters of perovskites can be controlled by controlling the stoichiometric ratio between rare earth metal A and transition metal B [3]. Among a wide range of perovskites, the LaCoO3 a rhombohedral perovskite and has been under continuous research for the last half century [4]. LaCoO3 perovskite based materials exhibit very fascinating applications because of their high electronic and electrical conductivity [5]. A great interest in the further applications of LaCoO3 based materials lie in substitution of La3+ with other rare-earth metal ions and in the same fashion, the Fe3+ can be replaced with other transition metal ions [6, 7]. There are several synthesis methods for the formulation of LaCoO3 such as pyrolysis [8], co-precipitation [9], hydrothermal [10] , micro emulsion [11] and sol-gel methods [12]. Among all these routes, some techniques like co-precipitation and micro-emulsion methods are very cheap and economic routes [6]. We have reported recently few new perovskites for structural, dielectric, magnetic behavior evaluation for advanced technologically applications [11, 13-16]. Here in the article, we plan to discuss the effect of highly paramagnetic Dy3+ and highly ferromagnetic Fe3+ metal ions

at L3+-site and Co3+-site respectively in LaFeO3 perovskite nanoparticles, fabricated by coprecipitation method. 2. Experimental Work 2.1 Synthesis of La1-xDyxCO1-yFeyO3 nanoparticles La1-xDyxCo1-yFeyO3 nanoparticles with composition (x,y=0 to 0.60) were prepared via coprecipitation method [17] by using LaCl3.7H2O (Sigma-Aldrich, 98 %,), DyCl3.7H2O (SigmaAldrich, 99%), (CH3.COO)2.Co.4H2O (BDH analar, 98%), (Fe(NO3)3.9H2O (Sigma-Aldrich, 98%), and Aqueous NH3 (BDH 35%). All the chemicals were used as such without any further purification. The required concentration of representing metal salts solutions were prepared in deionized water and stirred on a magnetic hot plate at ~50-60 oC. Aqueous ammonia solution (~ 2 M) was used to raise the pH value to 9-10. After maintaining the pH all the reaction mixtures were stirred for 5-6 h at room temperature continuously. The precipitates were washed using distilled water to reduce the pH to ~7. The precipitates of all compositions were dried in oven at 100

o

C and annealing was carried out at 700 oC for 7 hrs in a temperature controlled muffle

furnace Vulcan A-550 at heating rate 5 oC/min. The annealed samples of all compositions were grinded into powder form and were characterized by various techniques. 3. Results and Discussion 3.1 Thermogravmetric Analysis (TGA) Thermal studies of un-annealed sample La1-xDyxCo1-yFeyO3 was carried out by SDT Q600 V8.2 Build 100 thermal analyzer at heating rate of 10o C/min under the Nitrogen atmosphere. Figure 1 shows the typical TGA curve for un-annealed La1-xDyxCo1-yFeyO3 nanoparticles. Total weight

loss was ~ 17%, which can be divided in five stages. In first stage ( 100 ) about 2% weight loss was observed, that is attributed to presence moisture contents in the material. In second stage at 240

about 4% weight loss was found which was due to tapped water inside the pores

of the. The later stages of weight loss are attributed to the conversion of metal hydroxides into metal oxides, and the conversion of metal oxides into perovskite structure. This TGA trend of newly synthesized La1-xDyxCo1-yFeyO3 nanoparticles is found compatible with already reported metal oxides nanoparticles [14]. 3.2 FTIR analysis Typical FTIR spectrum of annealed La1-xDyxCo1-yFeyO3 nanoparticles was recorded on Nexus 470 spectrometer at room temperature in the range of 400 cm-1 to 4000 cm-1 (Figure S1, Electronic Supplementary Information). The main purpose of FTIR studies was to examine the metal-oxygen boding that is required in structural elucidation [18]. The main FTIR bands

in

La1-xDyxCo1-yFeyO3 nanoparticles FTIR spectrum were observed at 554.8 cm-1 (Dy-O),425.1 cm-1 (Fe-O) and 1382.2 cm-1 (La-O) [7, 11, 14]. 3.3 SEM analysis Scanning electron microscopic (SEM) analysis for the La1-xDyxCo1-yFeyO3 was carried out using Joel JSM-6490A electron microscope. Typical SEM images is shown in the Figure 2 .SEM images of La1-xDyxCo1-yFeyO3 showed that prepared particles have size in the range of 20 to 60 nm. In the SEM image, most of the particles are found as spherical, besides some are found as elongated with aggregation behavior [19]. Metal oxide particles aggregation have also been reported earlier in literature [6, 20, 21] [14].

3.4 XRD analysis X-ray diffraction pattern of all compositions of La1-xDyxCo1-yFeyO3 nanoparticles were recorded at Philips X’ Pert PRO 3040/60 diffractometer with Cu Kα as radiation source.The powder XRD spectra of perovskite nanoparticles La1-xDyxCo1-yFeyO3 of all samples are shown in the Figure 3. All peaks match with standard pattern of LaCoO3 (01-084-0847). This suggested that prepared materials possess orthorhombic phase. The crystallite size of all samples of La1-xDyxCo1yFeyO3nanoparticles

determined by scherrer formula [22] was found in the range 25-70 nm. The

lattice parameters “a”, “b” and “c” were calculated by using the cell software with the help of XRD data [1]. The lattice parameter “a”, “b”and “c” decreased as the concentration of Dy-Fe increased .This decrease is assigned due to smaller ionic radii of Dy3+ (0.90 Å) and Fe3+ (0.64 Å) as compared to La3+ (1.03 Å) and Co3+ (0.72 Å) respectively [23]. The substituted nanoparticles were also found to exhibit the different XRD peaks intensities, that is justified by inherent variable sensitivity of different metals to the XRD peak intensities [15, 24]. The cell volume of La1-xDyxCo1-yFeyO3 perovskite nanoparticles was decreased by increasing the Dy-Fe concentration. This decrease is assigned due to smaller ionic radii of Dy (0.90 Å and Fe ( 0.64 Å) as compared to La (1.03 Å) and Co (0.72 Å) respectively. The decrease of cell volume confirmed the substitution of La and Co with Dy and Fe respectively [25]. However difference in ionic radii between La and Dy was more as compared to the difference between Co and Fe, therefore the net result was decrease in cell volume. The difference in cell volume of each composition further confirmed the successful substitution of corresponding metal ions at proper positions [26, 27].

3.5 Magnetic Properties Magnetic measurements were carried out at vibrating sample magnetometer VSM Lakeshore74071 at 298k. The hysteresis loops of La1-xDyxCo1-yFeyO3 nanoparticles are shown in Figure 4. The nanocrystalline samples with x and y=0.15 and 0.30 showed ferromagnetic behaviors. However the other compositions exhibited the paramagnetic nature. Various magnetic parameters like saturation magnetization (Ms), remanence (Mr) and coercivity (Hc) values were determined from the hysteresis loops are listed in Table 2 and their trend with dopants is depicted in Figure 5. It is obvious from the Figure 5 that the magnetic parameters (Ms, Mr and Hc) were increased as the content of Dy and Fe increased, and for higher contents, the magnetic parameters were decreased [28]. The composition La0.85Dy0.15Co0.85Fe0.15O3 (x, y = 0.15) exhibited the maximum Ms and Mr values. However the maximum retentivity was observed for La0.70Dy0.30Co0.70Fe0.30O3 perovskite nanoparticles. The increase in Ms and Mr is presumably due to substitution of La with Dy and CO with Fe, La behaves is paramagnetic (having zero unpaired electrons) replaced by Dy, which has highly magnetic moment with 5 unpaired electrons in their f-orbital. Due to five unpaired electrons, Dy showed maximum magnetic moment [25]. Because of this property of nanoparticles they can be utilized for recording media purpose. The Hc increased with the increase contents of Dy-Fe [29]. 3.6 DC-Electrical Resistivity The dc-electrical resistivity of La1-xDyxCo1yFeyO3 nanoparticles was measured in the temperature range ~300 to 700 K by a two point probe method. The effect of temperature and dopant contents (Dy3+ and Fe3+) was evaluated and discussed as follows. All the DC-resistivity curves for all compositions are shown in Figure 6. At the decreased temperature, the resistivity was found

relatively high [30].The electric resistivity can be explained on the basis of two basic existing theories, which are Arrhenius and modified interpolator hopping model. However mostly the hopping mechanism is used to explain the temperature dependence electric resistivity. According to this mechanism, the electrical conduction in nanoparticles is due to hopping of electrons between the ions of the same element but of different valance states present at the octahedral sites [31]. The conduction in nanoparticles occurs due to the results of hopping of electrons between Co+3 and Co+2 ions that are present. The Effect of temperature on the resistivity could be explained on the basis of hopping conduction mechanism as shown below.

Co 3  O  Co 2  Co 2  O  Co 3 At high temperature the exchange of the electrons between Co 3 to Co 2 becomes high that resulted high conductivity and resistivity decreased. The resistivity decreases with increased temperature and then becomes constant high temperature. The decreased resistivity with increasing temperature indicating the semiconductor behavior of metals [28].The nanoparticles with compositions x, y ≤0.30 exhibited interesting temperature dependence behavior that is called as metal to semiconductor transition. This behavior suggested that these materials can be utilized fabrication of switching materials. The effect of Dy and Fe on the resistivity is shown in the Figure 7. The Figure shows the variation of electrical resistivity as a function of Dy and Fe . For x and y=0 i.e. LaCoO3 very low value of resistivity was observed. This resistivity was found to increase as the La and Co were replaced by Dy and Fe respectively. The minimum resistivity was firstly observed when x,y=0 was 0.77819

108

. By increasing Dy and Fe

concentration the resistivity was increased .The maximum value of resistivity was 12.54

108

was exhibited by La0.40Dy0.60Co0.40Fe0.60O3 nanoparticles. The significantly increase in

resistivity is due to the decreased electron exchange between same element of variable oxidation states. La was replaced by Dy which is rear earth metal and show the unique magnetic behavior, due to this conductivity decrease and resistivity increases. This 12 fold increase in resistivity is due to the reduced hopping conduction in Dy-O-Dy as compared to that of La-O-La. Because of very high resistivity these materials can be used for microwave devices fabrications [14]. 3.7 Dielectric Parameters Dielectric parameters were evaluated by using Wayne Ker WK6500B precision instrument of all the prepared samples at 298 K. The frequency range was kept 100 Hz to 5×106 Hz. The variation in dielectric constant, dielectric loss, dielectric tangent loss were determined and are shown in Figure 8, Figure S2 and Figure S3 respectively. High values for dielectric parameters (dielectric constant, dielectric loss, and dielectric loss tangent) were observed at low frequency, that were decreased with the increased frequency. The observed behavior of dielectric dispersion can be explained on the basis of Maxwell-Wagner model and Koop’s phenomenological theory. According to this theory, the dielectric medium consists of well conducting grains, which are separated by poorly conducting grain boundaries. In the low frequency region boundaries play the main role however at high frequency grains are the main contributors [32]. The response of electron hopping decreased with the increase of frequency and therefore the dielectric parameters decreasesed in high frequency range [1]. According to Maxwell-Wagner theory both dielectric constant and dielectric parameters are inversely proportional with frequency. At low frequency high values of dielectric tangent loss was observed and become approximately constant at higher frequencies [1, 32, 33]. The dielectric parameters at selected frequencies are given in table 3 [34]. The maximum dielectric constant (ε = 154.34) was observed for LaCoO3 at 0.03 MHz

frequency, however the minimum value (ε = 50.8) was observed for La0.4Dy0.6Co0.4Fe0.6O3 nanoparticles at the same frequency.

4. Conclusion Dy and Fe doped LaCoO3 nanoparticles in the range of 20-60 nm were fabricated via cheap economic chemical co-precipitation route. Effect of dopants (Dy3+ and Fe3+ on structural, magnetic, electrical and dielectric parameters was successfully investigated and correlated. All magnetic parameters like Ms, Mr and Hc were enhanced several times by Dy and Fe substitution in LaCoO3 nanoparticles. DC resistivity was also ~12 fold enhanced. All these results suggest the La1-xDyxCo1yFeyO3 nanoparticles as potential candidates for various technological applications. 5. Acknowledgement One of the authors (I. Shakir) highly acknowledges the Deanship of Scientific Research King Saud University for its funding (Prolific Research Group PRG-1436-25).

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List of tables

Table 1: Cell parameters (a, b and c), cell volume and crystalline size measured for La1-xDyxCo1-yFeyO3 nanoparticles. Parameters

x =0.00

x=0.15

x=0.30

x= 0.45

x=0.60

Lattice constant a/Å

5.3696

5.3696

5.3696

5.3696

5.3696

Lattice constant b/ Å

5.354

5.3402

5.3290

5.3401

5.3200

Lattice constant c/ Å

5.345

5.3362

5.3185

5.3250

5.3000

153.663

152.433

151.311

152.361

150.2424

Cell Volume/Å 3

Crystallite Size/nm

60.757

70.165

52.532

26.244

52.544

Table 2: Various magnetic parameters La1-xDyxCo1-yFeyO3 perovskite nanoparticles.

Magnetic Parameters

x =0.00

x=0.15

x=0.30

x= 0.45

x=0.60

Coercivity (Hc)/Oe

780.9

739.81

862.96

248.45

235.98

Magnetization (Ms) (emu/g)

0.47865

16.93003

14.58172

3.33322

2.7341

6.17029

5.65

0.09776

0.08075

Retentivity (Mr) 0.05686 (emu/g)

Table 3: Various dielectric parameters for La1-xDyxCo1-yFeyO3 nanoparticles at some selected frequencies. Parameters

Frequency

x,y =0

x,y=0.15

x,y=0.30

x,y=0.45

x,y=0.60

Dielectric Constant

0.03MHz

154.34783

98.1

55.71998

61.00138

50.8

2.51MHz

5.04348

29.2

20.7268

22.42654

18.7

4.01MHz

4.16522

27.6

20.1072

21.42558

17.9

5MHz

3.84348

26.9

19.83748

20.97449

17.5

0.03MHZ

15.01616

85.55074

44.19158

44.84047

44.84047

2.51MHz

0.10272

5.63358

2.13173

3.50632

3.50632

4.01MHz

0.07368

4.99974

1.83115

3.10086

3.10086

5MHz

0.06341

4.76343

1.72318

2.90805

2.90805

0.03MHz

3

0.87181

0.7931

0.73507

0.88209

2.51MHz

0.63

0.19296

0.10285

0.15635

0.18762

4.01MHz

0.546

0.18103

0.09107

0.14473

0.17367

5MHz

0.509

0.17683

0.08686

0.13865

0.16638

Dielectric Loss

Tan δ

Figure 1: TGA/DTA curves of La1-xDyxCo1-yFeyO3 nanoparticles.

Figure 2: Typical SEM image of La1-xDyxCo1-yFeyO3 nanoparticles.

Figure 3: XRD pattern of La1-xDyxCo1-yFeyO3 nanoparticles.

Figure 4: Hysteresis loops for the La1-xDyxCo1-yFeyO3 nanoparticles.

Figure 5: Variation of saturation magnetization, remanence and coercivity with Dy-Fe contents.

Figure 6: Effect of temperature on the resistivity of La1-xDyxCo1-yFeyO3 nanoparticles.

Figure 7: Effect of dopants on the resistivity of La1-xDyxCo1-yFeyO3 nanoparticles.

Figure 8: Effect of frequency on the dielectric constant of La1-xDyxCo1-yFeyO3 nanoparticles.

Highlights 

La1-xDyxCo1-yFeyO3 nanoparticles were prepared in the range 20-60 nm.



12 fold increase in DC resistivity achieved for La0.40Dy0.60Co0.40Fe0.60O3.



Paramagnetic to ferromagnetic behavior was observed for La1-xDyxCo1-yFeyO3 nanoparticles.