**Abstract**

This study explored the structural and dielectric features of Mg0.5Tm0.5Fe2O4 (Tm = Zn and Cu) that were synthesized by the Solid-state reaction (SSR) method. The X-ray powder diffraction (XRD) analysis reveals that the prepared samples are single-phase cubic structure without any impurity. Rietveld-refined X-ray diffraction results reveal the formation of cubic structure and all the peaks of Mg0.5Zn0.5Fe2O4 and Mg0.5Cu0.5Fe2O4 are perfectly indexed in the cubic (*Fd*-3 *m*) structure. Dielectric constant and dielectric loss variation with frequency were also explored. Both decrease when the relevant alternating field is increasing and become constant at high frequencies which reflects the important role of interfacial polarization. Furthermore, the Mg0.5Cu0.5Fe2O4 having the smallest crystallite size (~ 44.73 nm) has a high dielectric constant (~ 4.41 × 104 ) value as compare to Mg0.5Zn0.5Fe2O4.

**Keywords:** solid-state synthesis, ferrite, crystallite size, X-ray diffraction, dielectric properties

### **1. Introduction**

Ferrites are insulating magnetic oxides with high electrical resistance, low dielectric losses, high permeability, and high saturation magnetization. These magnetic materials are special and can be used in several device applications. Transition metal ion-doped spinel ferrites are fascinating due to high dielectric constant and low dielectric losses [1, 2]. Soft ferrite materials such as Mg-Zn ferrites have vast technological importance due to their relatively high Curie temperature, low cost, and eco-friendly stable nature. The transport properties of soft ferrites are mainly controlled by divalent impurities. Further, soft ferrites are used in advanced technologies such as magnetic resonance imaging (MRI), magnetic drug delivery, microwave absorbers, catalysis, detoxification of biological fluids, transformer cores, magnetically controlled transport of anti-cancer drugs, sensors [2].

Spinel ferrites with formula AB2O4 (A = Mg, Zn, Cu) have a cubic structure with an *Fd*3*m* space group. However, MgFe2O4 is having an inverse spinel structure with zero magnetic moments. This inversion is usually affected by the temperature given during calcination, while ZnFe2O4 often has a normal spinel structure without magnetic moment. Due to low Neel temperature both the ferrites show antiferromagnetic characteristics. It shows paramagnetic behavior due to weak superexchange interaction at room temperature [3, 4]. The polycrystalline Mg-Zn inverse spinel ferrites are commonly represented by (ZnxMgyFe1-x-y)[Mg1-x-yFe1+x+y]O4, where Zn2+ ions are bound to the tetrahedral sites (interstitial) and Mg2+ ion occupy the B sites [octahedral]ions have an affinity towards the interstitial (tetrahedral) site and Mg2+ ions occupy octahedral sites. However, Fe3+ ions occupied at both the tetrahedral and octahedral sites [5]. The effect of Cu ion doping on Mg-Zn ferrites should be investigated as the copper ferrites possess a tetragonal structure and Mg-Zn ferrites retain the spinel structure [6].

The materials having high dielectric constant and low dielectric losses are useful in microwave devices that make transition metal and rare earth doped Mg-Zn ferrite an attractive candidate. The dielectric properties are largely influenced by the method of synthesis, chemical structure, doping concentration, grain structure, calcination temperature, and the size of the dopant [7]. The previous studies have provided important findings on the frequency-dependent dielectric properties as the value of dielectric constant for MgFe2O4 is 57.93 at 10 Hz [8], for ZnFe2O4 is 2641 at 1 kHz [9], for Mg0.75Zn0.25Fe2O4 is 740 at 100 Hz and for Mg0.5Zn0.5Fe2O4 is near to ~50 at 100 Hz [4] whereas the dielectric constant of all these materials decreases with an increase in the frequency.

We have to use the solid-state reaction method to synthesize the Mg0.5Tm0.5Fe2O4 (Tm = Zn and Cu) ferrites. The key benefits of solid state reaction synthesis over other methods are that it is simple, cheaper, and convenient. It also requires less solvent, reduces contamination, and gives high yields of products. The present chapter mainly focuses on the crystal as well as the dielectric response of Mg0.5Tm0.5Fe2O4 (Tm = Zn and Cu) ferrite. The techniques used for the characterization of Mg0.5Tm0.5Fe2O4 (Tm = Zn and Cu) are X-ray diffraction (XRD) and dielectric measurements.

### **2. Experimental details**

The Mg0.5Tm0.5Fe2O4 (Tm = Zn and Cu) samples were synthesized using a Solid-state reaction technique. All chemicals used here were of analytical grade without any further purification. Precursors such as zinc oxide (ZnO), magnesium oxide (MgO), ferric oxide (Fe2O3), and CuO (copper oxide) with 99.9% purity were combined in stoichiometric amounts and thoroughly mixed using a mortar pestle. The resulting powder was calcined in a muffle furnace open to the air at 1000 °C for 12 hours creating a solid sample that was again ground with mortar and pestle into a fine powder. The sample was reground and calcined again for 12 h at 1050 °C to increase the homogeneity of the prepared samples. Each heat treatment included a heating and cooling rate of 10 °C/min and with intermediate grindings. Further, an organic binder called polyvinyl acetate (PVA) is added to the powder sample to binds the particles. The obtained powder samples were compressed in the circular shape of 1 mm thick and 10 mm diameter pellets using a hydraulic press following the application of 8 tons of pressure. At last, the pellets were fully sintered at 1200 °C for 12 h, then steadily cooled to room temperature.

The X-ray diffraction patterns of the Mg0.5Tm0.5Fe2O4 (Tm = Zn and Cu) were recorded at ambient conditions using a Bruker D8 advanced diffractometer with a copper anode (1.5460 Å) in Bragg–Brentano geometry. This equipment possesses a LynxEye detector based on the silicon drift detector technique. The X-ray diffraction patterns were obtained in the 2θ angle range from 20 to 80°, using a step size

**47**

**Figure 1.**

*XRD patterns of Mg0.5Tm0.5Fe2O4 (Tm = Zn and Cu) ferrites.*

*Effect of Transition Metal on Structural and Dielectric Properties of Mg0.5Tm0.5Fe2O4…*

of 0.02°. The powder-diffraction data was processed by Rietveld refinements using the FullPROF program [10]. The dielectric properties of these samples have been tested in the impedance analyzer with the model-Novo control tech Germany alpha ATB, which is usable within the frequency range of 3 μHz-20 MHz and the *ac* voltage range from 100 mV to 3 V. The high temperature silver paste was used on their

A powder X-ray diffraction (XRD) analysis was used to determine the crystallinity and purity of prepared samples. The room temperature XRD pattern with indexed hkl for the prepared samples of Mg0.5Tm0.5Fe2O4 (Tm = Zn and Cu, and henceforth designated as Mg0.5Zn0.5Fe2O4 and Mg0.5Cu0.5Fe2O4, respectively) samples are depicted in **Figure 1**. The XRD pattern of Mg0.5Zn0.5Fe2O4 indicates the presence of a single-phase, whereas the Mg0.5Cu0.5Fe2O4 sample shows minor impurity peaks which is due to the presence of minor secondary phase corresponds

The observed diffracted peaks support the formation of a cubic spinel-type structure with the space group *Fd-*3 *m* and all the diffracted peaks are compared with the Joint Committee on Powder Diffraction Standards (JCPDS) data and match well with the Card No. 86–2267 [5]. The magnified view of the most pronounced peak (311) of Mg0.5Zn0.5Fe2O4 and Mg0.5Cu0.5Fe2O4 samples are shown in the inset of **Figure 1**. We observe that there is a slight shift occurring for each intensity peak as compared to Mg0.5Zn0.5Fe2O4 towards the higher angle side. This shifting is taking place due to the minor difference in the ionic radii of Cu2+ (0.72 Å)

*DOI: http://dx.doi.org/10.5772/intechopen.96729*

two major surfaces for dielectric measurements.

to unreacted monoclinic CuO phase (space group C2/c).

**3. Results and discussion**

**3.1 Structural analysis**

and Zn2+ (0.74 Å) ions.

*Effect of Transition Metal on Structural and Dielectric Properties of Mg0.5Tm0.5Fe2O4… DOI: http://dx.doi.org/10.5772/intechopen.96729*

of 0.02°. The powder-diffraction data was processed by Rietveld refinements using the FullPROF program [10]. The dielectric properties of these samples have been tested in the impedance analyzer with the model-Novo control tech Germany alpha ATB, which is usable within the frequency range of 3 μHz-20 MHz and the *ac* voltage range from 100 mV to 3 V. The high temperature silver paste was used on their two major surfaces for dielectric measurements.
