https://doi.org/10.52131/jmps.2021.0201.0012 12 Journal of Materials and Physical Sciences Volume 2, Number 1, 2021, Pages 12 - 21 Journal Homepage: https://journals.internationalrasd.org/index.php/jmps Investigation of Structural, Spectral, and Dielectric Properties of Cd- Substituted NiCoPr Nano Ferrites Alina Manzoor1*, Muhammad Abubakar1, Amir Muhammad Afzal2, Muhammad Imran Arshad1, M. Nasir Rasul3 1 Department of Physics, Government College University, Faisalabad,38000, Pakistan 2 Department of Physics, Riphah International University, 13-Km Raiwind Road, Lahore-54000 Pakistan 3 Institute of Physics, The Islamia University of Bahawalpur, Bahawalpur-63100, Pakistan ARTICLE INFO ABSTRACT Article History: Received: February 24, 2021 Revised: April 29, 2021 Accepted: June 28, 2021 Available Online: June 30, 2021 The effect of cadmium ions on the structural, spectral, and dielectric properties of Pr doped Ni0.4Co0.6-xCdxFe1.95Pr0.05O4 ferrites synthesized by the self-ignited sol-gel process is investigated in the present work. The addition of cadmium ions in place of cobalt ions resulted in an increase in the lattice constant. X-ray diffraction experiment revealed the single- phase spinel structure. The obtained average crystallite size is ranging from 20 - 30 nm. By increasing the substitution of cadmium ions, the dielectric constant, dielectric loss (tan δ) and impedance are noted to increase. SEM study found the spherical grain morphology with some degree of agglomeration. The existence of pores, the sintering process, and the magnetic activity of the particles may be responsible for nanosized particles with a homogeneous particle size distribution. Raman spectra revealed a slight shifting in Raman modes with cadmium addition which may be attributed to the strain produced due to the presence of larger cadmium ions at the Fe3+ site. Keywords: XRD Raman Spectra Dielectric Impedance Sol-Gel Process © 2021 The Authors, Published by iRASD. This is an Open Access article under the Creative Common Attribution Non-Commercial 4.0 *Corresponding Author’s Email: alinamanzoor@gmail.com 1. Introduction In the field of nanotechnology, devices and systems are designed, characterized, and implemented by regulating the shape and size of the materials. These controlled-sized materials are immensely used for industrial and domestic applications such as imaging, mechanical industries, telecommunication, catalysis, medical and environmental applications. Thus, nanotechnology advances the fundamental principles of nano-scale materials and their applications (Devan, Kolekar, & Chougule, 2006). With the decrease of particle size, the surface area of nano-sized materials increases which steer the quantum- size effect (Zhang et al., 2020). Due to the growing surface area, that is the principal navigating force to reduce sintering-temperature of the particles, and this reduces the free energy during sintering (Akhtar, Nazir, Tahir, Qamar, & Khan, 2020). The specific chemical and physical properties of nanoparticles make them highly appropriate for the design of new and improved materials and devices. Spinel ferrites are commonly used to monitor the propagation direction, frequency, amplitude, and phase of microwave signals in microwave devices. To maximize the construction of these devices and to aid in the production of ferrite, a precision measurement of dielectric and magnetic properties at working frequencies and temperature ranges is needed to work out (Lassoued & Li, 2020). In view of applications, the ferrites have become more fascinating because of their high resistivity values (102 - 1010 ohm-cm) that are nearly 15 times higher in magnitude than iron (Varma, Bharadwaj, & Babu, 2019). https://journals.internationalrasd.org/index.php/jmps mailto:alinamanzoor@gmail.com Alina Manzoor, Muhammad Abubakar, Amir Muhammad Afzal, Muhammad Imran Arshad, M. Nasir Rasul 13 Their applicability at high frequency, good resistance to heat, and greater corrosion resistance are other reasons that make them most significant. Ferrites are excellent soft magnetic materials for high-frequency applications due to low cost, high resistivity, and low eddy current losses that have been thoroughly tested for the application of multi-layer chip inductors (MLCI) (Junaid et al., 2020). The incorporation of rare earth (RE) ions in the lattice of spine ferrites leads to the RE-Fe linkage (4f-3d coupling), the reason behind the changes in the Curie temperature and magnetization of ferrites (Elayakumar et al., 2019). Moreover, the substitution of transition elements into a spinel structure drastically affects the structural, optical, magnetic, and dielectric properties (Pan, Sun, Han, Zhang, & Zhao, 2019). There are different methods to fabricate the nanocrystalline ferrites like sol-gel auto combustion or controlled combustion method, co-precipitation method, solid state reaction, and hydro-thermal methods etc. (Akhtar, Babar, Qamar, ur Rehman, & Khan, 2019; El Nahrawy, Soliman, Sakr, & El Attar, 2018; Huq, Saha, Ahmed, & Mahmood, 2013; Jalilvand & Faghihi-Sani, 2013). Among these, sol-gel is the most suitable method due using inexpensive precursors, good morphology, easy of handling, controlled size of particles, controlled composition, and homogeneity along with other advantages such as cost- effective method, highly reactive powder, low external energy consumption, and no need of special equipment. 2. Experimental Single phase Cd-substituted Ni0.4Co0.6- xCdxFe1.95Pr0.05O4 (x=0-0.6) nano-ferrites were synthesized via sol-gel self-ignition technique. The balanced stoichiometric amounts of all salts were taken. Citric acid with 1:1 M ratio was added into the nitrate solution as an oxidizing agent. The solution was stirred for 15-20 minutes to achieve a homogeneous solution and after that small amount of ammonia solution was added to attain pH 7 of the solution. The solution was constantly stirred with heating ON at 250 oC. The solution was converted into thick gel within 1 hour and after some time the auto combustion took place, and fluffy dark grey ferrite ash was collected. After fine grinding of grey ferrite powder, sintering was carried out at 900 oC. The final fine-grinded sintered samples were characterized through different techniques and their various properties were investigated in detail. XRD experiment was done to analyze the structural properties of material including crystalline size, lattice constant, cell volume, and X-ray density etc. The dielectric properties were analyzed through LCR technique. In order to explore the material’s morphology, chemical composition, and crystalline structure, scanning electron spectroscopy (SEM) was used. For the imaging of samples, secondary electrons and back-scattered main electrons are used. Intra- and inter-molecular vibrational information is provided by Raman spectroscopy which also provided the additional understanding of reactions that are useful for material identification. 3. Results and Discussion 3.1. XRD Analysis The X-ray diffraction patterns of all samples of Cd-substituted Ni0.4Co0.6- xCdxFe1.95Pr0.05O4 (x=0-0.6) are shown in figure 1. All necessary diffraction peaks can be seen from these XRD patterns that correspond to different planes; specified as (220), (311), (400), and (511). It is determined from these miller indices that the fabricated materials have a face centered cubic structure belonging to space group Fd3m (Valenzuela, 2012). The most intense diffraction peak (311) is found at 35.6 ̊ which considered as the characteristics peak of the spinel matrix. The recorded patterns are well matched with an ICDD card reference number 00-010-0325. It is observed that the lattice constant is changed enormously by changing the composition of the samples in figure 2. The value of lattice constant first increases for x=0.15 and after that it decreases for x up to 0.6. This decreasing effect is attributed to the smaller ionic radii of cadmium ions than that of the cobalt ions. The decrease in the lattice constant is primarily due to the contraction of the spinel lattice since the lattice starts to Journal of Materials and Physical Sciences 2(1), 2021 14 contract when smaller size Cd ions tried to replace the larger sized Co ions (Modak, Ammar, Mazaleyrat, Das, & Chakrabarti, 2009). 20 25 30 35 40 45 50 55 60 x = 0.60 x = 0.45 x = 0.30 x = 0.15 In te n s it y ( a .u ) 2 Theta (Degree) Ni 0.4 Co 0.6-x Cd x Fe 1.95 Pr 0.05 O 4 x = 0.0 (220) (311) (400) (511) Figure 1: Combine XRD patterns of Ni0.4Co0.6-XCdXFe1.95Pr0.05O4 ferrites 0.0 0.1 0.2 0.3 0.4 0.5 0.6 8.15 8.20 8.25 8.30 8.35 8.40 8.45 8.50 L a tt ic e c o n s ta n t Concentration Lattice Constant Å Figure 2: Graph between concentration and lattice constant The crystallite size (D) from each peak is calculated and then an average value of D is taken for each sample. The average value of crystallite size is ranging from 20-30 nm. A nonlinear variation in D is observed as a function of Cd concentration. Figure 3 represents the variation of crystallite size as a function of Cd concentration. It is observed that from the concentration x = 0 to x = 0.15 the crystallite size is drastically reduced and after that it increases. Alina Manzoor, Muhammad Abubakar, Amir Muhammad Afzal, Muhammad Imran Arshad, M. Nasir Rasul 15 0.0 0.1 0.2 0.3 0.4 0.5 0.6 20 22 24 26 28 30 32 C ry s ta l S iz e ( n m ) Concentration Crystal Size Figure 3: Graph between concentration and average crystallite size The X-ray density is calculated using the following relation. ρx= 8M/Na3 (1) Here, M is the molecular weight of the composition, N is the Avogadro number, and a is the lattice constant. The value of X-ray density is ranging from 5.41 to 6.16 g/cm3. It is observed that with increasing Cd substitution, the X-ray density is also increased. This increase in the X- ray density is due to the fact that the X-ray density is directly dependent on the molecular weight as well as on the lattice parameter (Gupta & Coble, 1968). As we have noticed that the lattice constant is decreased with the concentration while the atomic mass of Cd (112.4 amu) is greater than that of Co (58.93 amu). So, it is expected to increase the X-ray density. Figure 4: Graph between concentration and X-ray density Journal of Materials and Physical Sciences 2(1), 2021 16 3.2. SEM Study Scanning electron micrographic (SEM) images of representative ferrites samples doped with Cd and rear earth praseodymium showed the surface morphology (figures 5a- 5e). Samples are sintered at 900 oC and clusters of fine agglomerated spherical particles of uneven size are found almost homogeneously and uniformly distributed. The agglomeration is observed to reduce by increasing the Cd substitution. The replacement of Co by Cd leads to enhance the crystallinity of the materials. The agglomeration indicates the porous nature, particles of nanometer sizes, and a homogenous particle size distribution that can be responsible for the magnetic behavior of the particles. Analysis of the SEM images for cobalt ferrites doped with Cd and Pr showed that the samples are composed of smaller grains. These results are in line with the calculated Scherrer crystallite dimension, as discussed above, using the XRD data for cadmium doped cobalt ferrites. Figure 5a: SEM image of Ni0.4Co0.6Fe1.95Pr0.05O4 ferrite Figure 5b: SEM image of Ni0.4Co0.45Cd0.15Fe1.95Pr0.05O4 ferrite Alina Manzoor, Muhammad Abubakar, Amir Muhammad Afzal, Muhammad Imran Arshad, M. Nasir Rasul 17 Figure 5c: SEM image of Ni0.4Co0.30Cd0.30Fe1.95Pr0.05O4 ferrite Figure 5d: SEM image of Ni0.4Co0.15Cd0.45Fe1.95Pr0.05O4 ferrite Figure 5e: SEM image of Ni0.4Cd0.60Fe1.95Pr0.05O4 ferrite Journal of Materials and Physical Sciences 2(1), 2021 18 3.3. Raman Spectroscopy The Raman spectra of NiCoFe2PrO4 nano particles substituted by Cd2+ are shown in the figure 6. The Cd2+ ions have greater ionic radius to occupy the tetrahedral (A) site due to which the structural disorder of the sublattice of oxygen has increased. All 6 Raman active modes assigned as 2A1g (596 - 613 cm-1, 672 - 688 cm-1), Eg (292 - 305 cm-1), 3T2g (538 - 574 cm-1, 454 - 467 cm-1, 200 - 250 cm-1) can be seen in the spectra. A 1g active mode, usually referred to as the shoulder A1g (2), is a function of spinal ferrite reverse and combined. The vibration models of over 600 cm-1 conduct to stretch symmetrically the metal oxygen bond of the tetrahedral sites and to bend oxygen at octahedral positions in modes under 600 cm-1; both symmetrically and unsymmetrically. A slight shifting activity is found in Raman modes with cadmium substitution that can be attributed to the strain caused by the inclusion of the broader cadmium ions at the Fe3+ site. The tetrahedral site is symmetrically bent with Fe ion in relation to an oxygen atom by the Fe-O mode (Haque, Huq, & Hakim, 2008; Rahman & Ahmed, 2005). 0 200 400 600 800 1000 1200 1400 1600 1800 In te n s it y Raman Shift (cm -1 ) X = 0.60 X = 0.45 X = 0.30 X = 0.15 X = 0 A1g A1g Eg T2g T2g T2g Figure 6: Raman scattering of Ni0.4Co0.6-XCdXFe1.95Pr0.05O4 ferrites 3.4. Dielectric Study The room-temperature dielectric measurements are taken for a frequency range of 1 KHz to 107 Hz. The figure 7 has shown the variation in dielectric constant (έ) as a function of frequency (f) of the AC field applied. It shows the conductive behavior of un-doped and Cd doped cobalt ferrites. At lower frequencies, the value of dielectric constant is observed to be high which further decreases with increasing the frequency of applied field. This is a typical behavior of ferrites, already investigated and reported by various researchers (Akhtar et al., 2020; Caltun, Spinu, & Stancu, 2001). The contribution to conduction phenomenon in ferrites comes from four major processes; polarization contributions at lower frequencies, i.e., dipolar and space charge, electrical, ionic, and some of the polarization contributions at higher frequencies, allowing the dielectric constant (έ) to decrease. The space-charge polarization model holds two parts: the grains (more conductive layer) and grain boundaries (less conductive and more resistive). The accumulation of space charge carriers in a dielectric medium is preferred to move through a resistive part (grain boundaries) of the sample. So, a finite time is required by the charge carriers to position their axes in the direction of alternating electric field. Thus, by increasing the frequency, the charge carrier remained incapable to sustain with the field reversals and consequently dielectric constant starts to decrease (Nam, Jung, Shin, & Oh, 1995; Pardavi-Horvath, 2000). Alina Manzoor, Muhammad Abubakar, Amir Muhammad Afzal, Muhammad Imran Arshad, M. Nasir Rasul 19 1000 10000 100000 1000000 1E7 0 5 10 15 20 25 X=0.00 X=0.15 X=0.30 X=0.45 X=0.60 D ie le c tr ic C o n s ta n t Frequency (Hz) Figure 7: Graph between frequency and dielectric constant The overall value of dielectric constant is observed to decrease with an increase in Cd concentration. In addition, in nanosized ferrites, the number of grain boundaries are larger which causes high dielectric constant at lower frequencies, whereas low-dielectric grains at high frequencies have more contribution (Byun, Byeon, Hong, & Kim, 1999). The variation of loss tangent loss as a function of applied field frequency for all samples is represented in figure 8. It can be seen that the loss tangent is increases as the concentration of Cd ions increases while it increases with increasing the applied field frequency. 1000 10000 100000 1000000 1E7 0 5 10 15 20 25 X=0.0 X=0.15 X=0.30 X=0.45 X=0.60 L o s s t a n g e n t Frequency (Hz)  Figure 8: Graph between frequency and loss tangent Journal of Materials and Physical Sciences 2(1), 2021 20 The variation in impedance as a function of applied field frequency for all samples is represented in figure 9. The value of the impedance decreases as the applied field frequency increases, and it becomes almost constant at a point and seems to be independent of the frequency. By increasing the concentration of Cd ions, the value of impedance is also increased. For x > 0.45, there is a sudden increase in the impedance value. 1000 10000 100000 1000000 1E7 -1x10 7 0 1x10 7 2x10 7 3x10 7 4x10 7 5x10 7 6x10 7 7x10 7 8x10 7 9x10 7 1x10 8 1x10 8 Im p e d e n c e ( o h m ) Frequency (Hz) X=0.00 X=0.15 X=0.30 X=0.45 X=0.60 Figure 9: Graph between frequency and impedance 4. Conclusion Cd-substituted Ni0.4Co0.6-XCdXFe1.95Pr0.05O4 (x=0-0.6) nano-ferrites synthesized via sol-gel method are investigated for various properties. XRD results confirmed the development of fcc spinel structure with crystallite sizes ranging from 20 to 30 nm. The incorporation of Cd at Co positions leads to an increase in lattice constant from 8.194 Å to 8.457 Å and a decrease in X-ray density. 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