Sol Gel Auto-combustion Process Research Articles

Synthesis and Characterization of Spinel Ferrite Co0.8Fe2.2O4 Nanoparticle

Cobalt ferrite Co0.8Fe2.2O4 nanoparticles were prepared using the sol-gel auto combustion process. The effects of calcination temperature on structural, magnetic, and electrical properties were studied. The cubic spinel phase fashioning of ferrite structure was confirmed using Fourier Transform-Infrared Spectroscopy (FT-IR) and X-ray Diffraction Patterns (XRD). The size of the formed crystallite of ferrite samples is ranged from 24.530 to 49.067 nm and it is found to be dependent on calcination. According to the images, which were taken by a Field Emission-Scanning Electron Microscope (FE-SEM), the particle size increases with raising the calcination temperature. Energy Dispersive Spectrum (EDS) was used to confirm the presence of Co, Fe, and O in all samples. A Vibrating Sample Magnetometer (VSM) was used to study the magnetic properties such as coercivity, saturation magnetization, and remanence field for the as-burnt and calcined samples. All samples exhibited ferrimagnetic behavior. As the calcination temperature rises, saturation magnetization (M_s), remanent magnetization (M_r), and squareness ratio (M_r/ M_s) increased. This behavior is related to the spin canting and disturbance in the surface spin. At room temperature, the dielectric loss factor (ε''), dielectric loss angle (tanδ), dielectric constant (ε'), and the conductivity σ_ac of all samples were examined as a function of frequency using the LCR meter. The changes in dielectric properties have been characterized at frequencies ranged from 50Hz to 2MHz based on Koop's theory, Maxwell-Wagner polarization, and electron hopping. As frequency rose, all-dielectric properties exhibited natural behavior.

Effect of calcium solubility on structural, microstructure and magnetic properties of SrFe12O19

The synthesis of Sr1-xCaxFe12O19 (x = 0.0–1.0 at increments of 0.1) samples is reported via a sol-gel auto-combustion process. XRD data for Sr1-xCaxFe12O19 samples calcined at different temperatures indicates a) single-phase formation up to x = 0.20 in samples calcined at 900 °C, b) an increase in calcium solubility to 50 atomic % (x = 0.50) at 1200 °C, c) a decrease in lattice parameters and cell volume with increasing ‘x’ and d) the presence of segregated α–Fe2O3 phase for x > 0.50 at 1200 °C and for x ≥ 0.20 at 900 °C. As the maximum Ca solubility in SrM (SrFe12O19) phase has been observed at 1200 °C, most of the other characterizations have been performed on these samples only. An increase in grain size with ‘x’ was revealed in FESEM micrographs. Magnetic measurements show that in the x = 0.50 sample the maximum saturation magnetization (Ms) value is ≈ 70.67 emu/g. Coercivity (Hc) decreases monotonically, with an increase in Ca content in SrM (SrFe12O19), from 3822 Oe (x = 0.00) to 2045 Oe (x = 0.50). Among the samples calcined at different temperatures, coercivity (Hc) decreases monotonically from 5650 Oe to 3128 Oe with an increased calcination temperature for samples of x = 0.20. The samples could be vital for magnetic recording and applications as permanent magnets due to their excellent magnetic properties.

Evaluation of applicability of Nd- and Sm-substituted Y1-xRxMnO3+δ in temperature swing absorption for energy-related technologies

An attempt is undertaken to chemically modify YMnO3+δ by the partial substitution of Y with larger Nd and Sm, aiming to boost the oxygen storage performance in the temperature swing process. Single-phase (P63cm) Y0.95Nd0.05MnO3+δ and Y0.95Sm0.05MnO3+δ compounds are obtained in a sol-gel auto-combustion process followed by the annealing at 1000 °C in Ar. Both materials show improved oxygen storage capacity, however, doping with Nd3+ enables the effective operation in air – capacity reached 1453 μmol-O g−1, which is over 86% of the capacity in O2. As documented for the Nd-containing sample, oxygen absorption is accompanied by oxidation of Mn3+ to Mn4+, and no changes in the valence of neodymium occur. The reversible oxygen intake and release occur at exceptionally low temperatures for Y0.95Nd0.05MnO3+δ, as low as in the 201–240 °C range. This enables utilization of the recovery of low- and medium-temperature waste heat. In addition, the paper presents the impact of the preparation route of the material on the oxygen storage-related performance. It is shown that lowering of the annealing temperature allows to further increase the rate of O2 absorption, making the material a promising candidate for practical application, however, it results also in the presence of the secondary phases.

Evaluation of spectral, optoelectrical, dielectric, magnetic, and morphological properties of RE3+ (La3+, and Ce3+) and Co2+ co-doped Zn0.75Cu0.25Fe2O4 ferrites

Present work reports the synthesis of RE3+ (La3+, and Ce3+) and Co2+ co-doped Zn0.75Cu0.25Fe2O4 samples powder using sol-gel auto combustion process. Rietveld refinement established the spinel matrix with the space group (F d -3 m) and suggests that the uniform distribution of cations at the tetrahedral and octahedral lattice sites. The comparative study of crystallite size (D) was found using the Scherrer's relation, Scherrer's plot, Williamson-Hall (W–H), and Size-Strain (SS) plot methods for the as-prepared ferrites. The absorption band analysis confirmed the characteristic band absorptions lie in the frequency range of (577.82–418.84) 102 × m−1. Moreover, the electrical resistivity (ρ) measurements showed that the Co–Ce doped ZCF sample is highly resistive as compared to the other samples. The dielectric measurements revealed a dispersion pattern at lower frequencies and an almost frequency-independent pattern at higher frequencies. The field dependence of the dM/dH curve shows a magnetically well stable state and good crystallization cubic matrix of all the samples.

Micro-structural, dielectrical and magnetic properties of Cu2+ substituted Ni0.7Mn0.3-xCuxFe2O4 (x = 0.0, 0.05, 0.1, 0.15 and 0.2) nano-ferrites

The nano-ferrites with chemical formula Ni0.7Mn0.3-xCuxFe2O4 having × between 0.0 and 0.2 were prepared by sol-gel auto-combustion process. The XRD pattern presents quite a good evidence for the formation of ferrite spinel phase in all the prepared samples. The broad lines indicate that the particles are of nano-size. The SEM studies reveal about the uniformity and crystallinity of the materials and also the spherical shape of the grains. Rise in copper density leads to fall in dielectric constant (εr) due to the relocation of Fe3+ from B-position to A-position. The dielectric loss (tan δ) maxima location swings towards the lower frequency as composition of dopant rises. The saturation magnetization and net magnetic moment decline with rise in Cu composition. The ESR technique ropes the subsistence of non collinear magnetic structure as predicted by VSM measurements.

Sol-Gel Synthesis of Dy-Substituted Ni0.4Cu0.2Zn0.4(Fe2-xDyx)O4 Nano Spinel Ferrites and Evaluation of Their Antibacterial, Antifungal, Antibiofilm and Anticancer Potentialities for Biomedical Application.

BackgroundThe constant rise of microbial biofilm formation and drug resistance to existing antimicrobial drugs poses a significant threat to community health around the world because it reduces the efficacy and efficiency of treatments, increasing morbidity, mortality, and health-care expenditures. As a result, there is an urgent need to develop novel antimicrobial agents that inhibit microbial biofilm formation.MethodsThe [Ni0.4Cu0.2Zn0.4](Fe2-xDyx)O4(x≤0.04) (Ni-Cu-Zn) nano spinel ferrites (NSFs) have been synthesized by the sol–gel auto-combustion process and were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive x-ray (EDX) and transmission electron microscopy (TEM). The antimicrobial, antibiofilm and antiproliferative activities of Ni-Cu-Zn NSFs were also examined.ResultsThe XRD pattern confirms the secondary phase DyFeO3 and Fe2O3 for substituted Dy3+ samples, and the crystallite size ranged from 10 to 19 nm. TEM analysis of NSFs revealed that the particles were cube-shaped and 15nm in size. NSFs exhibited significant antimicrobial, antibiofilm and antiproliferative activity. At concentration of 1 mg/mL, it was found that the NSFs (ie, x=0.0, x=0.01, x=0.02, x=0.03 and x=0.04) inhibit biofilm formation by 27.6, 26.2, 58.5, 33.3 and 25% for methicillin-resistant Staphylococcus aureus (MRSA) and 47.5, 43.5, 48.6, 58.3 and 26.6% for Candida albicans, respectively. SEM images demonstrate that treating MRSA and C. albicans biofilms with NSFs significantly reduces cell adhesion, colonization and destruction of biofilm architecture and extracellular polymeric substances matrices. Additionally, SEM and TEM examination revealed that NSFs extensively damaged the cell walls and membranes of MRSA and C. albicans. Huge ultrastructural alteration such as deformation, disintegration and separation of cell wall and membrane from the cells was observed, indicating significant loss of membrane integrity, which eventually led to cell death. Furthermore, it was observed that NSF inhibited the cancer cell growth and proliferation of HCT-116 in a dose-dependent manner.ConclusionThe current study demonstrated that the synthesized Ni-Cu-Zn NSFs could be used to develop potential antimicrobial surface coatings agents for a varieties of biomedical-related materials and devices in order to prevent the biofilms formation and their colonization. Furthermore, the enhanced antiproliferative properties of manufactured SNFs suggest a wide range of biomedical applications.

Morphological analysis of Cu substituted Ni\Zn in Ni-Zn ferrites

Cu substituted Ni in Ni0.5-xCuxZn0.5Fe2O4 (x = 0, 0.05, 0.1, 0.15 and 0.2) samples and Cu substituted Zn in Ni0.5Zn0.5−xCuxFe2O4 (x = 0, 0.05, 0.1, 0.15 and 0.2) is synthesized using the sol-gel auto-combustion process. Recently, we have carried out their structural analysis using XRD and FTIR and found a cubic spinel structure. In this paper, we have studied their morphological and compositional structure with the help of a Scanning Electron Microscope (SEM) attached with an Energy Dispersive Spectrometer (EDS). The comparative study shows that the grain size of Cu substituted Ni is greater than Cu substituted Zn in Ni-Zn ferrite. These smaller grain-sized ferrites are preferred for many microstructural applications. Depending on the available magnetic field, sintering temperature, and atmosphere, they can have different nucleation, and hence their application mode is different. They can have a critical concentration that can tune their properties. The EDS attached with the SEM confirmed the proper composition of samples.
 BIBECHANA 18 (2) (2020) 80-86

Photooxidative decomposition and defluorination of perfluorooctanoic acid (PFOA) using an innovative technology of UV–vis/ZnxCu1-xFe2O4/oxalic acid

Per- and polyfluoroalkyl substances (PFAS) are a large group of perfluorinated organic molecules that have been in use since the 1940s for industrial, commercial, and consumer applications. PFAS are a growing concern because some of them have shown persistent, bioaccumulative and toxic effects. Herein, we demonstrate an innovative technology of UV–vis/ZnxCu1-xFe2O4/oxalic acid for the degradation of perfluorooctanoic acid (PFOA) in water. The magnetically retrievable nanocrystalline heterogeneous ferrite catalysts, ZnxCu1-xFe2O4 were synthesized using a sol-gel auto-combustion process followed by calcination at 400 °C. The combination of ZnxCu1-xFe2O4 and oxalic acid generate reactive species under UV light irradiation. These reactive species are then shown to be capable of the photodegradation of PFOA. The degree of degradation is tracked by identifying transformation products using liquid chromatography coupled with quadrupole time-of-flight mass spectroscopy (LC-QTOF-MS).

Synthesis, characterization and visible light-responsive photocatalysis properties of Ce doped CuO nanoparticles: A combined experimental and DFT+U study

In this work, CuO and Ce doped CuO (Ce:CuO) nanoparticles (NPs) were prepared by the sol-gel auto-combustion process. The effect of the concentration of Ce doping (0, 2%, 4%, 6%, and 8%) on the structural properties, surface morphology, electronic properties, optical properties, and visible light assisted photocatalytic activities of NPs were studied experimentally and also with Density Functional Theory (DFT + U) simulation. The X-ray Diffraction (XRD), Raman and Fourier transform-infrared (FTIR) studies confirmed the presence of Cu-O bonding in the as-prepared nanoparticles. Incorporation of Ce was found to introduce intrinsic defects in the Ce:CuO NPs and reduces the optical bandgap from 1.72 eV to 1.40 eV. The photocatalytic performance of the NPs was assessed by studying the degradation of methylene blue (MB) under visible light irradiation. Ce:CuO NPs exhibit better photocatalytic efficiency compared to pure CuO NPs. Furthermore, DFT based simulation predicted that the incorporation of Ce narrowed down the bandgap of the NPs due to the creation of shallow doping states near the valance and conduction bands. The reduction of band gap together with the presence of shallow dopant states allows efficient charge separation together with improved photon adsorption of Ce doped CuO NPs yielding an enhanced photocatalytic activity.

Modification of magnetic properties, energy band gap and conduction mechanism of lanthanum orthochromite via (Sm, Fe) codoping

We report our investigations on the magnetic, thermal, optical and dielectric properties of the nanocrystalline La0.7Sm0.3Cr1−xFexO3 (0 ≤ x ≤ 0.3) samples synthesized through sol–gel auto-combustion process. The maximum magnetization and coercive field increase in Fe-doped samples. Fourier transform infrared (FTIR) spectra reveal the metal–oxygen (Cr/Fe–O) stretching and bending modes of vibration. Thermal analysis illustrates the occurrence of structural phase transition at ~ 290 °C for the pristine sample, and the phase transition temperature rises with the increase in Fe concentration. The specific heat capacity at constant pressure also reflects this transition. The energy band gap reduces for the doped samples. Dielectric constant, dielectric loss and loss tangent exhibit the usual frequency dependence and decrease with the amount of Fe. The Giuntini law implies higher contribution of polaronic conduction in the doped samples. Electric modulus analysis also shows the manifestation of both short- and long-range-order conduction processes in this system. The Nyquist plots for both impedance and electric modulus emphasize that grains dominate the conduction process. Temperature-dependent impedance and electric modulus analysis established that the relaxation processes are thermally activated and deviate from the ideal Debye behaviour.

Structural analysis of Cu substituted Ni\Zn in Ni-Zn Ferrite

Ni-Zn ferrites are soft ferrites basically popular for high-frequency devices. They have low coercivity, low permeability, and higher resistivity. These properties have their own benefits on one hand but on the other hand, we can make them more efficient by doping suitable elements in order for tuning their properties for other applications. It this work, highly conducting Cu is used for substituting Ni in Ni-Zn ferrites and prepared Ni0.5-xCuxZn0.5Fe2O4 (x = 0, 0.05, 0.1, 0.15 and 0.2) samples using the sol-gel auto-combustion process. We have studied their resulting structural parameter using X-ray Powder Diffraction (XRD) and Fourier Transform Infrared (FTIR) Spectroscopy method and compared with that of Cu substituted Zn Ni-Zn ferrites. Their structures are found to be single-phase cubic spinel similar to that of Cu substituted Zn. The lattice constant increases with Cu concentration opposite to that at Zn substitution. Likewise, the size of the crystallites was not in monotonic change with the doping concentration in both cases due to internal strain and cation distribution. The difference in the pattern of XRD and FTIR of our samples indicate their different but significant properties. The changes in the structure show the effect of Cu doping and indicate the possible interesting changes in their electric, electronic, and magnetic properties.
 BIBECHANA 18 (2021) 128-133

Sol-gel Autocombustion Elaboration and Physiochemical Characterizations of Cu2+ Substituted Cobalt Ferrite Nanoparticles

Introduction:The copper doped cobalt ferrite series, with nominal formula CuXCo1-XFe2O4(X = 0, 0.25, 0.5, 0.75, 1), has been elaboratedviasol-gel autocombustion process by copper substitution procedure into cobalt ferrite framework.Methods:The five synthesized ferrites have been analyzed by X-ray powder diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy coupled to energy dispersive X-ray spectroscopy, complex impedance spectroscopy and superconducting quantum interference device magnetometry.Results and Discussion:The analysis of the results allowed to deduce that the cubic spinel basic structure was not modified by the incorporation of copper into the host lattice and the corresponding pure fine powders obtained formed by homogeneous nanoparticles. The highest electrical conductivity value, σDC(373K) = 27.03x10-3S.cm-1, was observed in the case of CuFe2O4.Conclusion:Moreover, the superparamagnetic behavior at room temperature has been confirmed by using both ZFC-FC and hysteresis magnetic measurement modes. In addition, the remarkable electrical conductivity and magnetic properties of the five explored nanoferrites, derived from the present investigation, enabled them useful in several modern nanotechnological and biomedical applications.

Design and development of Ga-substituted Z-type hexaferrites for microwave absorber applications: Mössbauer, static and dynamic properties

Gallium substituted Z-type Sr3GaxCo2-xFe24O41 (x = 0.0–2.0 in steps of 0.4) hexaferrites were synthesised by the sol-gel auto-combustion process, and sintered at 1150 °C. The structural, morphology, magnetic, Mössbauer, dielectric and microwave absorption properties were examined. XRD results of x = 0.0, 0.4, 0.8, and 1.2 samples show the formation of a single Z-type hexagonal phase. The samples x = 1.6 and 2.0 show the formation of Z and M phases. Hysteresis loops analysis suggest that samples x < 1.6 possess a soft magnetic nature, while the samples x = 1.6 and 2.0 show a hard ferrite characteristics. All samples possess multi-domain microstructures. The composition x = 0.4 [maximum MS = 97.94 Am2kg−1] was fitted with seven sextets (Fe3+) and a paramagnetic doublet-A (Fe3+), while beyond x ≥ 0.8 two more doublets (Fe2+) were observed along with seven sextets in Mössbauer spectra. The maximum values of Fe2+ ions (1.26%) and relative area of paramagnetic doublets (1.91%) were observed for x = 1.6 composition, which is also responsible for the lowest value of MS (69.99 Am2kg−1) for this composition. The average hyperfine magnetic field was found to decrease, whereas average quadrupole splitting was found to increase, with Ga-substitution. The substitution of Ga ions enhanced permeability, dielectric constant, magnetic loss and dielectric loss, in a non-linear fashion. The reflection loss was maximum at lower frequencies for samples x = 0.0 and 0.8, and decreases with frequency. Sample x = 0.8 has maximum reflection loss of −12.44 dB at 8 GHz, a measured thickness of 3 mm, and a bandwidth of −10 dB at 1.18 GHz. The observed absorption has been discussed with the help of the input impedance matching mechanism and quarter wavelength mechanism. The observed coercivity in different samples also influenced microwave absorption which demonstrated potenial in microwave absorber applications.

CaTiO3–Sm0.9Nd0.1AlO3 ceramics with a moderate dielectric constant and a high quality factor prepared by sol–gel auto combustion method

CaTiO3–LnAlO3 (Ln = La, Nd, Sm) is a perovskite-type microwave material system characterized by a moderate dielectric constant εr, a high quality factor Q × f, and a small temperature coefficient of resonant frequency τf, making this system promising for microwave devices. However, its high synthesis temperature and sintering temperature limit its industrial applications. In our work, single phase 0.7CaTiO3–0.3Sm0.9Nd0.1AlO3 (7CT–3SNA) was synthesized via the sol–gel auto combustion method using citric acid as fuel at a relatively low temperature. After being calcined at 600 °C for 2 h, well-crystallized 7CT–3SNA powders with 30–50 nm average particle size were achieved, suggesting good sintering activity. The new and narrow order band at about 800 cm−1 in the Raman spectra indicates a high ordering degree in the B site of 7CT–3SNA solid solution. Compared with the solid–state reaction method and co-precipitation method, the 0.7CT–0.3SNA ceramics fabricated by the current method possess a much lower calcination temperature, a similar εr value, and an improved Q × f value. The optimum microwave dielectric properties of εr = 43.54, Q × f = 54375 GHz, and τf = −6.3 × 10−6/°C are obtained for the CTSA ceramics derived from the sol–gel auto combustion process. Therefore, the 7CT–3SNA ceramics prepared in this study are potential dielectric materials for microwave applications, indicating that the sol–gel auto combustion method is a good alternative strategy for the fabrication of CaTiO3–LnAlO3 ceramics.

Correlation between structure, dielectric and multiferroic properties of lead free Ni modified BaTiO3 solid solution

Present study highlights the influence of Ni doping on the structural, optical, dielectric, ferroelectric and magnetic properties of nanocrystalline BaTi1-xNixO3 (0 ≤ x ≤ 0.06) ceramics synthesized by sol-gel auto combustion process. Phase identification and crystal structure are examined through Rietveld refinement analysis that ensures mono-phase nature with tetragonal crystal structure in P4mm space group. The observed variation in the structural parameters viz. lattice constants, unit cell volume, bond lengths (Ti-O) and bond angles (Ti-O-Ti) are the direct evidence of distortion produce in the unit cell under the effect of Ni doping. The FTIR studies confirm perovskite structure and presence of stretching/bending vibrations of the various bands present in the samples. The optical properties divulge a minor alteration in optical bandgap under the influence of Ni content. Dielectric studies reveal higher value of the dielectric constant for pristine sample in the low frequency region, but its value decreases on Ni doping. The dielectric response, analyzed through UDR model, exhibits deviation from linear behavior at higher frequencies. Ferroelectric measurements demonstrate that the pristine sample has higher values of remnant polarization (Pr) and maximum polarization (Pm) which decrease linearly with the increase in Ni doping. Magnetic hysteresis loops at room temperature establish a weak ferromagnetic nature of the samples that arises due to the carrier-mediated exchange interactions with smaller values of magnetic parameters. These investigations ensure that the ferromagnetism can be induced in BaTiO3 by appropriate doping of Ni ions, which may find their potential use in the field of multiferroics.

Structural confirmation and elucidation of spectral, optical and magnetic properties of cerium doped lead hexaferrite

Cerium ion doped M-type lead hexaferrite with chemical formula Pb1-xCexFe12O19 (where x = 0.0, 0.1, 0.2 and 0.3) were prepared using sol-gel auto combustion process. XRD patterns revealed that all diffraction peaks are in good agreement with magnetoplumbite mineral crystal structure. Unit cell ‘c’ value slightly decreases and ‘a’ value almost remains constant, when the concentration of Ce ion is increased. Magnetic properties were analysed using Vibrating Sample Magnetometer. It was observed that saturation magnetization (Ms), retentivity (Mr) decreases and coercivity (Hc) increases with increasing Ce concentration and the samples become more and more hard magnetic. Observed tetrahedral, octahedral and spinel block vibrations in Raman spectra establishes the molecular structure of synthesized samples. Optical transmission spectral analysis reveals that the samples are transparent in the entire visible region and the band gap are in the range 2.44–2.91 eV.

Synthesis of magnetic nickel ferrites nanocomposites: An advanced remediation of electroplating wastewater

Nickel ferrite nanocomposites (NFNCs) were prepared and utilized to remove hexavalent chromium from the effluent of the electroplating industry. The nickel ferrite nanoparticles (NFNPs) were synthesized by the sol-gel auto combustion process, and they were doped ultrasonically onto the surface-modified multi-walled carbon nanotubes (SM-MWCNTs). Characterization results confirmed that the NFNPs with a cubic spinel structure were successfully impregnated onto the SM-MWCNTs. The synthesized NFNCs were tubular structures with an outer diameter in the range of 30–40 nm and had high crystal defect. The NFNCs with the surface area of 210.5 m2 g−1 offer high magnetic separability due to their paramagnetic behavior. Non-linear kinetic, thermodynamic, and isotherm models were used for interpretations, and high Cr(VI) uptake of 129.83 mg/g was obtained at 40 °C. The Cr(VI) uptake by NFNCs was dominated by electrostatic attractions at a low pH and ion exchange mechanism at a higher pH. Lastly, high efficient recyclability of the NFNCs and applicability in removing other heavy metals from electroplating effluent suggested them to be a promising material in wastewater treatment.

Investigation of alteration in physical properties of dysprosium orthochromite instigated through cobalt doping

Abstract We report the systematic investigations on DyCr1–xCoxO3 (0 ≤ x ≤ 0.3) samples prepared through sol-gel auto combustion process. Rietveld refinement of the powder x-ray diffraction patterns assures the formation of mono-phase orthorhombic structure with space group Pbnm. In order to get an obvious view about the effect of substitution of Cr3+ with Co3+ ions on crystallographic parameters of these samples, the tilt angles, cell and orthorhombic distortions were calculated. The average crystallite sizes and lattice strain as computed from the Williamson-Hall analysis are found to rise with the increase in Co content. The porosity of the synthesized samples lies in between ∼30 and 38%. The Fourier transform infrared (FTIR) spectra of these samples affirm the formation of desired crystal structure. Field emission scanning electron microscopy (FESEM) images exhibit the existence of polycrystalline microstructure. The energy dispersive x-ray (EDX) analysis assures the elemental compositions of the prepared samples. UV/Visible spectroscopy is utilized to estimate the energy band gap, Urbach energy and threshold wavelength. The energy band gap reduces whereas Urbach energy and threshold wavelength enhance on increasing the cobalt content. Dielectric responses of these samples have been analysed in view of “universal dielectric response” model. AC conductivity increases with the increase in frequency and that affirm the small polaron hopping type of conduction mechanism in the investigated frequency range. The relaxation peaks appear in imaginary part of impedance spectra shift toward lower frequencies with the increase in Co concentration which indicates the higher values of relaxation time in the doped samples. Differential thermal analysis reveals the structural transitions and improved thermal stability of the Co doped samples.

Room temperature dual ferroic behavior induced by (Bi, Ni) co-doping in nanocrystalline Nd0.7Bi0.3Fe1−xNixO3 (0 ≤ x ≤ 0.3)

Nanocrystalline samples of Nd0.7Bi0.3Fe1−xNixO3 (x = 0, 0.1, 0.2, and 0.3) are synthesized using sol-gel auto-combustion process to investigate their structural, electrical, magnetic, and thermal properties. Phase purity and crystallinity of the samples are determined through x-ray diffraction (XRD) data. XRD patterns along with Rietveld refinement reveal orthorhombic structure with Pbnm space group. Unit cell parameters, bond angles, and bond lengths for all the samples have been determined. Crystallite size calculated by Scherrer equation is found to be in the range of 15–21 nm. The characteristic bands in the FTIR spectra further confirm the formation of our samples. FE-SEM images indicate the homogeneous distribution of particles on large scale and Ni-doped samples show some wall-like nanostructure in the morphology. EDX spectra confirm the elemental composition without any impurity element. The polarization versus electric field (P-E) and magnetization versus magnetic field (M-H) loops exhibit the multiferroic nature of the material. The sample with concentration x = 0.2 shows the maximum value of polarization (Pm) while maximum magnetization is achieved for x = 0.1 concentration. The specific heat capacity (Cp), endothermic, and exothermic peaks of the materials have been determined in the broad temperature range with the help of DTA measurements in the controlled nitrogen atmosphere. The Neel temperature of the parent system is found to be 742 K and that decreases up to 573 K on Ni doping.

Investigation of energy band-gap of the composite of hexaferrites and polyaniline

The Bi–Al doped M-type hexaferrite (BaFe11.8Bi0.1Al0.1O19) was prepared by the use of sol gel auto combustion process. The prepared sample was sintered at 1000 °C for 5 h. Polyaniline was synthesized by oxidative polymerization. Mechanical blending was used to synthesize BaFe11.8Bi0.1Al0.1O19-PANI composite. X-ray diffraction (XRD), Fourier Transform Infra-red spectroscopy (FTIR), Field Emission Scanning Electron Microscope, Energy Dispersive X-ray spectroscopy and UV–vis-NIR spectroscopy were used for structural and optical analysis. XRD spectra show pure single phase of M-type hexagonal ferrites. The presence of bands in FTIR spectra in the range of 400–600 cm−1 and 800–1600 cm−1 indicate possible formation of hexaferrite and PANI. The band gaps were found nearly 2.24, 2.36 and 2.21 eV for HP1, HP2 and HP3 respectively.