**2.2 Method**

The CuFe(2x)EuxO4 (where x = 0.00, 0.01, 0.02, 0.03) nanoparticles were synthesized by solution combustion method by using stoichiometry amount of copper nitrate, europium nitrate, and ferric nitrate as metal nitrates and carbamide and glucose as fuels. The weighed metal nitrates and fuels were taken in 250 ml borosil glass beaker; then all nitrates and fuels were diluted with distilled water and kept on magnetic stirrer about 45 min to obtain a homogeneous solution. This solution was kept in preheated muffle furnace at 450 10°C temperature to ignite, to get a copper ferrite nanoparticle. Obtained CuFe(2x)EuxO4 (where x = 0.00, 0.01, 0.02, 0.03) nanoparticles were taken in to mortar and then pestle it for getting fine powder of nanoparticles. The solution combustion technique flowchart for europium-doped copper ferrite as shown in **Figure 1**.

Cu-K<sup>α</sup> radiation of wavelength 1.5404 Å and the diffractogram run with two

*Flowchart to show solution combustion technique of synthesizing europium-doped copper ferrite.*

*Enhanced Humidity Sensing Response in Eu3+-Doped Iron-Rich CuFe2O4…*

*DOI: http://dx.doi.org/10.5772/intechopen.90880*

software. The Rietveld refined XRD pattern peaks confirm the polycrystalline

. The XRD data were refined by using full proof

theta (2θ) range from 10<sup>o</sup> to 80<sup>o</sup>

*Schematic illustration of humidity sensing setup.*

**Figure 1.**

**Figure 2.**

**77**

#### **2.3 Characterizations**

For as-synthesized CuFe(2x)EuxO4 (where x = 0.00, 0.01, 0.02, 0.03) nanoparticles, X-ray diffraction characterization was carried out by using

*Enhanced Humidity Sensing Response in Eu3+-Doped Iron-Rich CuFe2O4… DOI: http://dx.doi.org/10.5772/intechopen.90880*

Cu-K<sup>α</sup> radiation of wavelength 1.5404 Å and the diffractogram run with two theta (2θ) range from 10<sup>o</sup> to 80<sup>o</sup> . The XRD data were refined by using full proof software. The Rietveld refined XRD pattern peaks confirm the polycrystalline

structure with general formula Fd3m. The CuFe2O4 ferrite belongs to a general formula AB2O4 in which A is a divalent ion site occupied by the Cu2+ ions and B is a trivalent ion site occupied by Fe3+ ions. The rare earth-doped CuFe2O4 ferrites have been used in many fields such as electronic devices, drug delivery systems, cancer therapy, and magnetic recording [1]. Rare earth-doped ferrites are also useful in high voltage electronics due to its negligible eddy current losses, high electrical resistivity, high permeability, magneto-optical, and magnetoresistive properties [2–4]. Generally, the trivalent ions are lesser in size than a divalent ion, and hence exchange of cations among the A and B sites plays a vital role in studying the structural, morphological, dielectric, and humidity sensing behavior of spinel copper ferrites. Copper ferrite has considerable good attraction of potential applications in various devices, like cores in transformers and microwave absorption [3, 4]. Copper ferrite nanoparticles can be prepared by various techniques like sol-gel method, coprecipitation method, solution combustion method, etc. [5, 6]. Many researchers have explored the properties of spinel ferrites by doping with different larger rare earth ions like samarium, terbium, gadolinium, and cerium in it. The europium-doped copper ferrites can be used in high-frequency applications due to the rare earth-doped ferrites showing low dielectric loss, good sensing response, and low value of conductivity. Europium-doped copper ferrites are usually considered

In the present work, spinel copper ferrites were prepared by solution combustion method and then in Eu3+ ions will be incorporated to investigate its structural, morphological, dielectric, and humidity sensing behavior at room temperature.

The required oxidizers (metal nitrates), viz., copper nitrate [Cu(NO3)23H2O],

The CuFe(2x)EuxO4 (where x = 0.00, 0.01, 0.02, 0.03) nanoparticles were synthesized by solution combustion method by using stoichiometry amount of copper nitrate, europium nitrate, and ferric nitrate as metal nitrates and carbamide and glucose as fuels. The weighed metal nitrates and fuels were taken in 250 ml borosil glass beaker; then all nitrates and fuels were diluted with distilled water and kept on magnetic stirrer about 45 min to obtain a homogeneous solution. This solution was kept in preheated muffle furnace at 450 10°C temperature to ignite, to get a copper ferrite nanoparticle. Obtained CuFe(2x)EuxO4 (where x = 0.00, 0.01, 0.02, 0.03) nanoparticles were taken in to mortar and then pestle it for getting fine powder of nanoparticles. The solution combustion technique flowchart for

For as-synthesized CuFe(2x)EuxO4 (where x = 0.00, 0.01, 0.02, 0.03) nanoparticles, X-ray diffraction characterization was carried out by using

europium nitrate [Eu(NO3)35H2O], and ferric nitrate [Fe(NO3)29H2O], and reducing agents, viz., carbamide [NH2CONH2] and glucose [C6H12O6], all were

as inverse spinel ferrites.

**2. Experimental details**

**2.2 Method**

**2.3 Characterizations**

**76**

**2.1 Required oxidizers and fuels**

*Mineralogy - Significance and Applications*

purchased from S.D. Fine Chemicals, Mumbai, India.

europium-doped copper ferrite as shown in **Figure 1**.

spinel cubic structure. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) were carried out by using JEOL (Model JSM-840) instrument respectively to understand structural morphology and elemental analysis. The mean grain size of the particles was estimated from SEM micrographs by using ImageJ software. From SEM and EDS to understand structural morphology and elemental analysis. The AC eclectic parameters were measured over a range of frequencies from 50 Hz to 10 MHz using Wayne Kerr 6500B series impedance analyzer. For humidity sensing AC conduction studies, powder samples were pressed in the form of pellet under the hydraulic pressure of 5 tons. Further, two faces of these pellets were painted with silver paste for electrical contact. The pellet was held between two probes and then placed in a glass chamber through a rubber cork and the other end of the electrodes connected to the programmable HIOKI Digital Multimeter to record the resistance corresponding to various RH relative humidities from 11% RH to 97%. The schematic illustration of humidity sensing setup is shown in **Figure 2**.

matched with spinel cubic structure of JCPDS card number 74-2400 and the CuO impurity peaks observed at 38.87° and 48.96° (JCPDS 80-1268) [7, 8]. The lattice parameter is found to increase with increase in Eu3+ concentration due to difference in ionic radius. The ionic radii of Fe3+ (0.67 Å) are lesser than that of Eu3+ (0.99 Å) ions; this confirms the occupancy of europium on an octahedral site. The average crystallite size of CuFe2�xEuxO4 (where x = 0.00, 0.01, 0.02, 0.03) nanoparticles estimated from the Debye-Scherrer relation and the average particle size of all the samples were found to be in the range of 16–51 nm [9]. The strain values are

*=*

tetrahedral site (LA) and octahedral site (LB) is shown in **Table 1**.

*Enhanced Humidity Sensing Response in Eu3+-Doped Iron-Rich CuFe2O4…*

and O peaks are clearly seen with Cuo impurity peaks (**Figure 4(right)**).

are well matched with the crystallite size as shown in **Table 1**.

**Crystallite size D in nm**

*3.3.1 Variation of frequency with AC conductivity*

CuFe(2�x)EuxO4 (where x = 0.00) of EDS spectrum depicts Cu, Fe, and O peaks are clearly seen with Cuo impurity peak. The Eu3+ peak appeared in all samples except when x = 0, and its intensity of Eu3+ peak increase with europium concentration increases. The grain size distribution histogram of CuFe(2�x)EuxO4 (where x = 0.00, 0.01, 0.02, 0.03) nanoparticles is shown in **Figure 4(left)**, and the average grain size of CuFe(2�x)EuxO4 (where x = 0.00, 0.01, 0.02, 0.03) nanoparticles is estimated from SEM micrographs using ImageJ software. The average grain sizes of all the particles

**Figure 5** shows the variation of frequency with AC conductivity plots, respec-

x = 0.0 8.126 25 539.29 1.38 � <sup>10</sup>�<sup>3</sup> Fd3m 28 3.518 2.873 x = 0.01 8.131 16 540.23 2.14 � <sup>10</sup>�<sup>3</sup> Fd3m 30 3.520 2.874 x = 0.02 8.143 21 542.71 1.63 � <sup>10</sup>�<sup>3</sup> Fd3m 40 3.526 2.879 x = 0.03 8.154 51 544.91 6.98 � <sup>10</sup>�<sup>3</sup> Fd3m 33 3.531 2.883

**Strain Є (radian)** **Space group**

**Average grain size**

**Hopping length (Å) LA LB**

tively, for CuFe(2�x)EuxO4 (where x = 0.00, 0.01, 0.02, 0.03) nanoparticles

**Volume (Å<sup>3</sup> )**

*Structural parameters of the CuFe(2*�*x)EuxO4 (where x = 0.00, 0.01, 0.02, and 0.03) nanoparticles.*

hopping length of LA and LB is calculated, the hopping length increasing with increase in Eu3+ concentration. This happened because Fe3+ ions are replaced by the relative number of Eu3+ in octahedral site and the variation of hopping length of

The surface morphology and elemental analysis of the CuFe(2�x)EuxO4 (where x = 0.00, 0.01, 0.02, 0.03) nanoparticles were performed with scanning electron microscope and energy-dispersive X-ray spectroscope. From **Figure 4(left)** we can clearly see that all the particles are spherical in shape and exhibit smooth surface with an average grain size of 20–40 nm. All samples of the SEM micrographs show highly porous nature, and the appearance of the dry foamy powder is due to the evolution of the gases during the combustion process [10]. **Figure 4(right)** shows the EDS spectrum of CuFe(2�x)EuxO4 (where x = 0.00, 0.01, 0.02, 0.03) nanoparticles. The CuFe(2�x)EuxO4 (where x = 0.01, 0.02, 0.03) of EDS spectrum depicts Cu, Fe, Eu,

<sup>4</sup> and are tabulated in **Table 1**. Further, the

calculated by using equation *ɛ* ¼ *<sup>β</sup>cos<sup>θ</sup>*

*DOI: http://dx.doi.org/10.5772/intechopen.90880*

**3.2 SEM and EDS**

**3.3 Dielectric studies**

**Lattice parameters (Å)**

**Eu3+ content**

**Table 1.**

**79**
