Physicochemical Investigation of Synthesized Bismuth and Silver-Doped Bismuth Nanoferrites, And Their Dielectric Properties

Bismuth nano ferrite and silver-doped bismuth nano ferrite are synthesized by the sol-gel method. The synthesized compound is characterized through several characterization methods such as the X-ray diffraction method, Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), and UV-Visible spectral studies. The X-Ray diffraction confirms bismuth nano ferrite has a Rhombohedral structure and belongs to the R-3m space group, and the silver-doped bismuth nano ferrite has an orthorhombic structure and belongs to the Cmcm space group. The crystallite size is calculated through Scherrer’s formula, the bismuth nano ferrite has a crystallite size of 20 nm, and the silver-doped bismuth nano ferrite has a crystallite size of 36.33 nm. FTIR studies confirm the formation of ferrite and indicate the metal ion group observed the peak shift after doping in the fingerprint region. The metal ion peaks are presented at 446.7 cm−1 and 527.8 cm−1 but after doping they shifted to 453 cm−1, 534 cm−1. The UV-Visible spectral analysis identifies the change in the energy band gap through a tauc plot, initially the energy band gap of bismuth nano ferrite is about 2.79 eV but after doping it reduces to 1.61 eV. the surface morphology is determined by SEM analysis and it provides 30 nm and for the doped compound 37 nm average particle size. Dielectric study confirms doping of silver to the bismuth gives more improved results which will be helpful at the application level such as in memory devices, photocatalysis, water splitting, and gas detection.


Introduction
Ferrites are a special type of magnetic material that are extensively employed in several technological applications.In addition to iron oxide, they may also contain other metal oxides [1].High magnetic permeability, electrical conductivity, and exceptional chemical stability are all characteristics of ferrites Based on their crystal structure, ferrites may be categorized into several groups, such as spinel ferrites (AB2O4), hexagonal ferrites (BaFe12O19), and garnet (perovskite) ferrites (Bi3Fe5O12) [2].Bismuth nano ferrite has a perovskite structure with a cubic unit cell and a corner-centered lattice.Bismuth ions (Bi 3+ ) and iron ions (Fe 3+ ) are arranged in precise patterns in the unit cell.The magnetic and electrical characteristics of bismuth nano ferrite are determined by the arrangement of these ions.Because of these arrangements, the ions show both ferroelectric and magnetic characteristics.Bismuth nano ferrite has an array of applications in the files of spintronics, data storage, energy harvesting, and sensing [3].It is often employed in high-temperature sensors because of its high Curie temperature.Bismuth nano ferrite can also be utilized in solar cells and as a catalyst in chemical processes, as well as in biological applications like drug delivery systems and imaging agents [4,5].The fundamental disadvantage of bismuth nano ferrite is its high leakage current caused by oxygen vacancies and mixed iron valence.These flaws compromise the efficiency and stability of bismuth nano ferrite devices.To compensate for the shortcomings of bismuth nano ferrite, silver can be doped into it to produce silver-doped bismuth nano ferrite.Silver doping decreases the band gap of bismuth nano ferrite and enhances its electrical conductivity.Silver-doped bismuth nano ferrite has potential uses in photocatalysis, water splitting, and gas detection [6].There are numerous ways for synthesizing bismuth and silver-doped bismuth nano ferrite, including the sol-gel approach, co-precipitation method, hydrothermal method, sonochemical method, microwave-assisted method, and combustion method.However, the sol-gel technique is an essential, cost-effective, and simple approach to adopt since it provides good control over the size and form of 1300 (2024) 012038 IOP Publishing doi:10.1088/1757-899X/1300/1/012038 2 the particles so this method is very convenient, and in the present study, the nanoferrites are synthesized utilizing the sol-gel method.The motivation of this study is to reduce the band gap of bismuth nano ferrite by doping and to study the physicochemical properties of both synthesized compounds [7,8].

2.2Procedure for Synthesis
In the present study, the synthesis of bismuth nano ferrite and the silver-doped bismuth nano ferrite is done through the Sol-Gel method.Bismuth nitrate, Ferric nitrate, and Citric acid are initially taken in the ratio of 1:2:3.While doping, silver nitrate is added to the mentioned compounds and the new ratio becomes 0.06:0.94:2:3.For a homogeneous mixture of the solutions, all the purchased nitrates are first dispersed separately in deionized water for three hours using a magnetic stirrer.Next, the solutions are combined into a large glass beaker and stirred for 3 hours.To maintain the pH value, Ammonia is added dropwise until the pH value reaches nine.The solution mixture is then heated for 2 hours at 70°C, and then raised to 90°C for an hour, where gel formation occurs, and then rise the temperature to 110°C the gel is converted into fluffy ash which will be collected and ground with the help of mortar and pestle to achieve a homogeneous compound.The compound is calcined at 200°C for 2 hours to remove impurities after which the compound is collected and characterized [9].113), (300), and (220), and impurities are denoted by the mark '#' for some 2θ angles; where α-Fe2O3 are the impurities which are found in the synthesized compound.By comparing the synthesized Bismuth nanoferrite (BNF) to the reference data from the JCPDS card no.00-014-0181, which has a Rhombohedral structure belongs to the R-3m space group which validates the crystal system, and the crystalline phase information was discovered.
Where D is the average crystallite size, K is the Scherrer constant (0.89), λ is the wavelength of the Xrays employed, β is the diffraction peak's full width at half maximum (FWHM) value, and θ is the diffraction angle.Utilizing the Debye-Scherrer formula, we can calculate crystallite size for BNF and ABNF.It was found that BNF is 20 nm in crystallite size, while ABNF is 36.33 nm in crystallite size [11].From Figure 2, the FTIR spectra of BNF and ABNF can reveal many different functional groups, such as Bi-O, Fe-O, and Ag-O.It is confirmed that ferrites form at about 446.7 cm -1 , 453 cm -1 , 527.8 cm -1 , and 534 cm -1 , respectively, corresponding to the stretching and bending modes of Bi-O, Fe-O, and Ag-O.A peak near 811.6 cm -1 and a peak near 1394.7 cm -1 correspond to nitrate ions and a peak near 2342.6 cm -1 corresponds to nitrile ions.The O-H groups were found as a result of water molecules stretching and bending at about 2122.8 cm -1 , and 2030.8 cm -1 as a result of insufficient water removal during synthesis or adsorption of water molecules from the air.Accordingly, FTIR confirms doping by revealing the shifting of the peaks from initially 446.7 cm -1 and 527.8 cm -1 to 453 cm -1 , and 534 cm -1 after doping [12].) ( )

FTIR analysis
In equation ( 2) "α" denotes the absorption coefficient, "h" represents the Planck's constant, "ν" is the frequency, "Eg" denotes the energy bandgap, and the "n" value is taken as 2 for the direct band gap and 1/2 for indirect band gap.The tauc plot of prepared NPs for direct permitted transition is shown in Figures 3.1 and 3.2.The energy band gap is obtained by projecting the tangent of the linear area towards the X-axis.The band gap for BNF samples is 2.79 eV, but the band gap for ABNF sample is 1.61 eV, owing to a change in electronic structure caused by the oxygen vacancy near the band edge.It has been discovered that when crystalline size increases, the energy band gap decreases.Furthermore, the shift in the energy band gap might be attributed to the phase transformation of BNF to ABNF.Because of this, ABNF is well suited for sensors, spintronics, data storage, and so forth [13].4.6.The average particle size of BNF is 30 nm and for ABNF is 37 nm [14].

Dielectric properties
Where the ε' represents the real component of the dielectric constant.C is identified as the capacitance in the above equation, and the thickness of the pellet is represented by t, whereas A represents the cross-section area of the pellet.tan Equation ( 4) represents the imaginary component of the dielectric constant (ε'') and the dielectric loss tangent is represented by tanδ.
Equation ( 5) represents the AC electric conductivity of the synthesized compounds, whereas f represents the frequency in Hertz.The real component ε' exhibits frequency-dependent behavior in the dielectric analysis of BNF.Due to the presence of multiple polarization mechanisms at low frequencies, such as domain wall motion, space charges, and impurities, ε' exhibits a high value.The value of ε' decreases with increasing frequency, demonstrating the opposition to polarization.The relaxation mechanisms within the material are thought to be the cause of this frequency-dependent activity.ABNF has a significantly lower real part ε' than BNF, suggesting a lower electrical energy storage capacity suggests a lower capacity for electrical energy storage.This decline can be attributable to the increased conductivity brought on by the doping of silver.The flow of charge carriers is made easier by the presence of Ag ions, which lowers ε' by reducing polarization [15].
Additionally, frequency-dependent is the imaginary portion ε'' of the dielectric constant for BNF.When exposed to an electric field, it exhibits heat as a representation of energy loss.Low energy dissipation is suggested by the fact that ε'' is very modest at low frequencies.Nevertheless, when the frequency rises, ε'' grows as a result of the greater contribution of relaxation processes, such as dipolar relaxation and ionic conduction [16].The imaginary portion ε'' of the dielectric constant in ABNF will change in a similar manner as the real part.Higher values of ε'' are obtained as a result of the conductivity improvement brought on by the doping of silver.As shown in BNF, this higher energy dissipation is accompanied by an enhanced frequency dependency of ε''.primary cause of the rise in conductivity is a result of the charge carrier's hopping frequency continuously rising.The Maxwell-Wagner and Koop phenomenological theories describe the idea of AC electric conductivity [17].While it was claimed that the frequency of electron hopping between Fe 3+ and Fe 2+ is lower and that the grain boundaries are more active at low frequencies.Due to the increased activity of conductive grains at higher frequencies, the hopping of electrons between Fe 3+ and Fe 2+ ions rise with frequency.From the Figure 5.3, we can see that the ABNF exhibits more electric conductivity than the BNF combination.This indicates that adding silver to the bismuth nano ferrite boosts its AC electric conductivity, making it a better material for application in electronic devices [18].

Conclusion
In the present study, the bismuth and silver doped bismuth nano ferrite is synthesized by solgel method and to know its physio-chemical properties several characterizations have been done such as XRD, FTIR, UV-visible study, SEM, and the dielectric properties has been observed and studied.Through the XRD study, the crystallite size found, for BNF is 20 nm, and for the ABNF is 36.66nm crystallite size.The FTIR plot confirms the metal ion group presence in the fingerprint region.The SEM gives the enhanced image of the synthesized particles where the BNF has the agglomerated images and the ABNF has the grain-like structures.The energy band gap for BNF is 2.7 eV and for the ABNF the band gap is about 1.61 eV.From this, we can observe that doping enhances the electric properties of the synthesized nanoferrites.In the dielectric properties, the real part and the imaginary part of the dielectric constant were determined and the AC electric conductivity study has also been done.Hence from these dielectric studies it is found that as the frequency increases the real and the imaginary part of the dielectric constant also increases and the same thing happens in the AC-electric study.Hence these things lead to several applications like photocatalysis, water splitting, gas detection, and many more.

Figure 1 .
Figure 1.XRD patterns of BNF and ABNF X-ray diffractometry (XRD) is an important tool for analyzing the crystallographic structure of materials by observing how X-rays interact with the sample.XRD study of bismuth nano ferrite revealed the existence of 10 distinctive intensity peaks at 2θ angles of 22.52°, 30.34°, 32.06°, 33.38°, 35.84°, 39.64°, 45.92°, 51.34°, 57.28°, and 67.24° correspond to the miller indices (101), (110), (012), (202), (113), (300), and (220), and impurities are denoted by the mark '#' for some 2θ angles; where α-Fe2O3 are the impurities which are found in the synthesized compound.By comparing the synthesized Bismuth nanoferrite (BNF) to the reference data from the JCPDS card no.00-014-0181, which has a Rhombohedral structure belongs to the R-3m space group which validates the crystal system, and the crystalline phase information was discovered.

Figure 2 .
Figure 2. FTIR graph of BNF and ABNF

Figure 4 . 5 .
Figure 4.5.Histogram plot for BNF Figure 4.6.Histogram plot for ABNF The surface morphology of the BNF and ABNF is determined by using the scanning electron microscope.The SEM images of BNF, i.e.Figure 4.1 shows the clear grain-like patterns in the image and confirm the formation of BNF through EDX which is shown in Figure 4.2.This indicates the presence of bismuth, iron, and oxygen compounds in the composite, and a little bit of carbon content is found in the composite it may be due to calcination.The SEM images of ABNF show a little bit of agglomerated grain-like patterns as shown in Figure 4.3 and the doping of Ag to the compound BNF is confirmed by the EDX through Figure 4.4.Here silver (Ag) peak appears along with the compound's bismuth, iron, and oxygen hence it confirms the doping.The average size of the nanoparticles is calculated through the histogram graph, which is shown in Figures 4.5and 4.6.The average particle size of BNF is 30 nm and for ABNF is 37 nm[14].
Figure 4.1 shows the clear grain-like patterns in the image and confirm the formation of BNF through EDX which is shown in Figure 4.2.This indicates the presence of bismuth, iron, and oxygen compounds in the composite, and a little bit of carbon content is found in the composite it may be due to calcination.The SEM images of ABNF show a little bit of agglomerated grain-like patterns as shown in Figure 4.3 and the doping of Ag to the compound BNF is confirmed by the EDX through Figure 4.4.Here silver (Ag) peak appears along with the compound's bismuth, iron, and oxygen hence it confirms the doping.The average size of the nanoparticles is calculated through the histogram graph, which is shown in Figures 4.5 and

Figure 5 . 1 .
Figure 5.1.The real part of the dielectric constant for BNF& ABNF compounds

Figure 5 .
1 shows the real part of the dielectric constant for BNF & ABNF compounds.

Figure 5 .
2 shows the imaginary part of the dielectric constant for BNF & ABNF compounds.