Mossbauer Analysis Research Articles

MOSSBAUER STUDIES OF NATURAL MINERAL RAW MATERIALS OF KAZAKHSTAN FOR BAUXITE-BASED PROPPANTS

The main problem at the oil and gas field is hard-to-recover reserves. The article discusses promising modern methods of increasing oil recovery. The analysis of widely used methods of extraction of hard-to-recover oil and gas reserves is carried out. The Mossbauer studies of the domestic natural mineral raw materials of proppants based on bauxite and aluminum oxides were carried out in order to study the structural and phase features of these materials. Proppants used in hydraulic fracturing to hold cracks play an important role in the oil and gas industry. The Moessbauer method is a powerful tool for studying the structure and electronic state of atoms in materials. It is based on the phenomenon of nuclear gamma resonance absorption and provides information about the chemical environment of the nucleus. In this study, proppants based on bauxite and aluminum oxides were used, which were subjected to a Mossbauer analysis.

Aluminum and Zinc Co-substituted Cobalt Ferrite: Structural, Magnetic, and Magnetostrictive Properties

We report on the influence of Al and Zn co-substitution on the structural, magnetic, and magnetostrictive properties of cobalt ferrite (Co1–xZnxFe2–xAlxO4, 0 ≤ x ≤ 0.15; CZFAO) materials, which were made using a glycine-nitrate autocombustion process. The cubic spinel structure is present in both the as-synthesized and the sintered CZFAO samples, where it was evident that the crystallite size and lattice parameter reduced with increasing x due to the incorporation of smaller Al3+ ions in place of larger Fe3+ ions in spinel ferrite. Co-substitution induced changes in the metal–oxygen bond lengths, causing both the tetrahedral and octahedral infrared and Raman spectroscopic bands to shift toward higher wavenumbers. The electron microscopy analyses indicate that the Al–Zn substitution induces grain growth, leading to a dense, interconnected grain morphology. Mossbauer analyses indicate that the Al3+ occupies the octahedral site, whereas Zn2+ is substituted at the tetrahedral site. Due to equal magnetic dilution of both tetrahedral and octahedral sites caused by the presence of Zn and Al at the appropriate sites, the saturation magnetization MS of CZFAO is the same as that of pure CFO. All other magnetic parameters (coercivity HC, magnetocrystalline anisotropy constant K1, and Curie temperature TC) decrease with increasing x, where the decline observed is mostly due to superexchange interaction (A-O-B) reduction caused by the substituents’ non-magnetic character. CZFAO materials exhibit higher magnetostriction strain λ and strain sensitivity dλ/dH at relatively low magnetic fields; among all the samples, x = 0.15 demonstrates a maximum strain sensitivity of −2.53 × 10–9 m/A at 23 kA/m magnetic field. The composition-tuned CZFAO materials with desirable properties are suitable for application in torque sensors.

Structural, Magnetic, and Optical Studies of Ni–Mg Ferrites Synthesized by Polyol Method

Magnesium and nickel‐substituted ferrites belong to an important class of spinel ferrites with wide variety of applications. Herein, preparation and characterization of pure, single‐phase Ni–Mg ferrites using a cost‐effective method, which yield high‐quality nanosized particles with good chemical homogeneity, are reported. A series of NixMg(1−x)Fe2O4 nanocrystalline powders (x = 1,0.75,0.5,0.25,0) is prepared using polyol method and a detailed investigation on the effect of dopant substitution on microstructural magnetic as well as optical properties is conducted. The as‐prepared samples are subsequently characterized using X‐ray diffractometer (XRD), X‐ray photoelectron spectroscopy (XPS), Fourier‐transform infrared spectroscopy (FTIR), Field‐emission scanning electron microscope (FESEM), Brunauer, Emmett, and Teller (BET), Mossbauer spectroscopy, Vibrating sample magnetometer (VSM), and UV–visible diffuse reflectance spectroscopy. Rietveld refinement confirms the single‐phase cubic structure with Fd‐3m (227) space group of NixMg(1−x)Fe2O4 series. The cation distribution can be represented as [Mg(1−x−y)Fe(δ)]A[Mg(x)Ni(y)Fe(2−δ)]BO4. FTIR bands at the finger print region of ferrites and Mossbauer analysis confirms the proposed cation distribution from Rietveld refinement. The magnetic nature is confirmed from Mossbauer and VSM analysis. In VSM, the saturation magnetization of the samples exhibits an increasing trend with nickel substitution. The optical studies of the series NixMg(1−x)Fe2O4 are conducted by UV–visible diffuse reflectance spectroscopy.

Microstructure, Magnetic and Mössbauer Studies of Mechanically Alloyed FeCoNi Nanocrystalline Powders

Magnetic structures have attracted a great interest due to their multiple applications, from physics to biomedicine. Iron, nickel and cobalt are among the most important ferromagnetic elements, therefore the synthesis of Fe-based alloys processed by ball milling from the Fe, Ni and Co powders is of particular interest. This subject mainly concerned the structural and magnetic properties evolution of Fe50Co25Ni25 nanocrystalline powder mixture prepared by mechanical alloying in a high-energy planetary ball mill under argon atmosphere. For extended milling time of 100 h, two nanocrystalline Fe (Co,Ni) (∼ 87 nm) and fcc-Co-rich (∼ 47 nm) phases were identified. This phase transformations, dependent on the alloying time, are related to the increase in dislocations and accumulation of stacking faults. Dislocation density of 1.25 × 1015 m−2 is estimated after 100 h of milling. The milled FeCoNi alloy displays a soft ferromagnetic behavior with single magnetic domain (Hc ∼ 12.5 Oe and Mr/Ms ∼ 0.007 for 100 h milling). Mossbauer analysis gives three main magnetic components: two different components attributed to metallic Fe species located in bcc and fcc Fe–Co–Ni domains and a magnetic component characterized by larger hyperfine fields and isomer shifts typical of Fe3+, Fe2+ species and Fe ions.

Surpassing electrocatalytic limit of earth-abundant Fe4+ embedded in N-doped graphene for (photo)electrocatalytic water oxidation

Abstract Developing highly active, cost-effective, and environmental friendly oxygen evolution reaction (OER) electrocatalysts facilitates various (photo)electrochemical processes. In this work, Fe3N nanoparticles encapsulated into N-doped graphene nanoshells (Fe3N@NG) as OER electrocatalysts in alkaline media were reported. Both the experimental and theoretical comparison between Fe3N@NG and Fe3N/NG, specifically including in situ Mossbauer analyses, demonstrated that the NG nanoshells improved interfacial electron transfer process from Fe3N to NG to form high-valence Fe4+ ions (Fe4+@NG), thus modifying electronic properties of the outer NG shells and subsequently electron transfer from oxygen intermediate to NG nanoshells for OER catalytic process. Meanwhile, the NG nanoshells also protected Fe-based cores from forming OER inactive and insulated Fe2O3, leading to high OER stability. As a result, the as-formed Fe4+@NG shows one of the highest electrocatalytic efficiency among reported Fe-based OER electrocatalysts, which can as well highly improve the photoelectrochemical water oxidation when used as the co-catalysts for the Fe2O3 nanoarray photoanode.

Influence of addition of Al3+ on the structural and solid state properties of nanosized Ni–Zn ferrites synthesized using malic acid as a novel fuel

Abstract In this work, the synthesis of Ni0.7Zn0.3Fe2-xAlxO4 (x = 0.0–0.6) nanoferrites by combustion method using malic acid as a novel fuel is being reported for the first time. The structural analysis of the nanosized ferrites was carried out by using XRD and IR studies. The cation distribution of all the ferrites was predicted using the Rietveld refinement data and was well supported by the Mossbauer analysis. The XRD parameters were calculated using this predicted cation distribution. The theoretical lattice constant matched exactly with the lattice constant obtained from the Rietveld refinement confirming the predicted cation distribution. The morphology of all the ferrites was studied using the SEM microscopy from which the particle size distribution was calculated along with the EDS mapping which confirmed the presence of all the constituent elements in all the ferrite samples. The dielectric properties of all the ferrites as a function of frequency as well as temperature were studied. The influence of substitution of magnetic Fe3+ by non-magnetic Al3+ in the ferrite series was also studied. It was observed that the addition of non-magnetic Al3+ in ferrites decreases the lattice parameter, density, saturation magnetization, and the Curie temperature. The FC-ZFC magnetization curve revealed a decrease in blocking temperature (TB) with an increase in Al3+ concentration in Ni0.7Zn0.3Fe2-xAlxO4.

Preparation of a novel functionalized magnetic nanobiocomposite as a carrier for protein adsorption

This study aims the synthesis of a novel functionalized magnetic nanocarrier based on xanthan gum biopolymer. Glycidyl methacrylate was grafted on xanthan gum chains by radical polymerization reaction using two types of initiators: ammonium persulfate and benzoyl peroxide. Characterization studies of the magnetic nanocarrier were performed using several instruments such as Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy, Energy-Dispersive-X-Ray Spectroscopy, X-Ray Diffraction Spectroscopy, Transmission Electron Microscopy, Mossbauer Spectroscopy, and Vibrating Sample Magnetometer. According to the Vibrating Sample Magnetometer data and Mossbauer analysis, Fe atoms were incorporated successfully in the polymer chains in Fe3+ state and magnetic nanocarrier has super-paramagnetic behavior, respectively. Epoxy groups on magnetic nanoparticles were converted to carboxylic acid groups using iminodiacetic acid and then tested to usability as a carrier for immobilization of proteins such as albumin, lipase and cytochrome c. The adsorption of albumin and lipase on magnetic nanoparticles were pH-dependent while cytochrome c was immobilized in a wide range of pH value. The calculated maximum experimental immobilization capacity of magnetic nanoparticles was 65.10 mg g−1, 62.0 mg g−1 and 188.0 mg g−1 for albumin, lipase and cytochrome c, respectively. Experimental data fitted to Langmuir isotherm better than Freundlich. The rate of cytochrome c adsorption followed the pseudo-second-order kinetic. Results showed that the functionalized magnetic nanoparticles can be effectively used as a carrier for protein separations, especially for cytochrome c. Moreover, the functionalized magnetic nanocarrier had high affinity to Cytochrome c protein even in multiple protein systems.

Investigation of the crystal/magnetic structure, magnetic and optical properties of SrYxNbxFe12−2xO19 (x ≤ 0.05) hexaferrites

Series of Sr hexaferrites (HFs) co-substituted with Nb3+ and Y3+ ions (SrYxNbxFe12−2xO19 (x ≤ 0.05) were prepared via sol-gel combustion method. In addition to their optical, low temperature, magnetic properties and hyperfine interactions were investigated in detail. X-ray diffraction (XRD) patterns were considered proving both the formation and pureness of products. Mossbauer analysis indicated that the hyperfine field on iron nuclei at all sites decrease with substitution of Y3+–Nb3+ ions into Sr-hexaferrite as a result of changing the magnetic Fe3+ (5 μB) ions by nonmagnetic Y3+ and Nb3+ ions. This leads to decreasing of the magnetic super exchange interaction between the ions. Measurements of AC susceptibility and ZFC-FC magnetizations implemented in a range from room temperature (RT) down to around 2 K. The analysis of MFC–MZFC data proves the ferrimagnetic performance of different prepared HFs in the whole range of 2–325 K and a super-spin glass-like behavior was identified at minimal temperatures. The investigation of AC susceptibility revealed a weakening in the magnetic exchange interactions with the rise in the Nb3+ and Y3+ ions ratios.

Co-Doped Rare-Earth (La, Pr) and Co-Al Substituted M-Type Strontium Hexaferrite: Structural, Magnetic, and Mossbauer Spectroscopy Study

The present study investigates the influence of La3+ and Pr3+ doping on the structural, magnetic properties, and hyperfine fields of Sr0.7RE0.3Fe12-2x CoxAlxO19, (RE: La3+ and Pr3+, x = 0.0 - 0.8) hexaferrite compounds prepared via auto-combustion technique. The XRD analysis shows a linear decrease in a and c lattice and unit cell volume contraction with the content x. The room temperature magnetic study shows that for the Pr3+ doped Sr0.7Pr0.3Fe12-2x CoxAlxO19 (Pr3+-SrM), the magnetization value monotonically decreases while for La3+ doped Sr0.7La0.3Fe12-2xCoxAlxO19 (La3+-SrM) magnetization value shows a noticeable increase in magnetization value with x. The coercivity of the Pr3+-SrM compound was observed to decrease while that of the La3+-SrM compound showed a marked 40% increase at x = 0.2 (~5829 Oe) in comparison to undoped SrFe12O19 (~3918 Oe). A difference in Curie temperature was also observed, with Tc ~ 525°C at x = 0.4 for Pr3+-SrM and Tc = 505°C for x = 0.4 for La3+-SrM compound. The observed differences in magnetic properties have been explained on the basis of the site occupancy of Co2+ and Al3+ in the presence of rare-earth ions. The presence of non-magnetic rare-earth ion, La3+, improved saturation magnetization, and coercivity and deemed suitable replacement for Sr2+. The hyperfine parameters namely quadrupole shift showed a decrease with the La3+ or Pr3+ doping independent of (Co2+-Al3+) ions doping. Overall, the Mossbauer analysis suggests that the (Co2+-Al3+) impurities prefer occupancy at 2a site.

Influence of Ho–Ni–Mn substitution on the structural and magnetic behavior of Ba–Sr Co2Z-type nanohexaferrites extension up to Mossbauer investigations

A series of Co2Z-type Ba–Sr nanohexaferrites Ba1.5Sr1.5Co2−zHozMnxNiyFe24−x−yO41 (z = 0.0, 0.05, 0.10, 0.15, 0.20, x = y = 0.0, 0.25, 0.5, 0.75, 1.00) have been synthesized using sol–gel auto-combustion synthesis route. The effect of Ho–Ni–Mn substitutions on crystallographic and magnetic properties of synthesized nanohexaferrites was investigated using XRD, VSM, and Mossbauer spectroscopy. Microstructural analysis showed single-phase crystal structures without any impurities and hexagonal with the space group P63/mmc. The average variation in crystallite size ranges from 43 to 60 nm with a slight increase in X-ray density and appreciable decrease in porosity was observed for different dopants. FE-SEM (Nova Nano SEM-450) substantiates the hexagonal structure and HR-TEM images assisted with SAED pattern confirm the crystalline quality and FWHM of the material, which significantly support the XRD results. FTIR spectra showed two characteristic metal stretching peaks in the range of 400–600 cm−1 due to the substitution of Ho–Ni–Mn. Magnetic measurements show maximum magnetic saturation (Ms) at 44.04 emu g−1 and elevated value of coercivity (Hc) 224Oe imparting typical characteristics of soft ferrite with high coercivity. Mossbauer analysis with least squares fit sextets of six distinguishable sites at room temperature for all samples substantially supports the results of VSM. The materials with large coercivity are useful in permanent magnet applications. The prepared composites could be useful for applications in microwave absorbing materials, magnetic storage, and the miniaturization of antennas for wireless communication devices.

Correction to: Ca2+/Mg2+ co-substituted strontium nanohexaferrites: magnetic investigation and Mossbauer analysis

Correction to: Ca2+/Mg2+ co-substituted strontium nanohexaferrites: magnetic investigation and Mossbauer analysis

Ni0.4Cu0.2Zn0.4TbxFe2-xO4 nanospinel ferrites: Ultrasonic synthesis and physical properties.

The Fe3+ ions were replace with Tb3+ ions as highly paramagnetic rare earth element within the structure of Ni0.4Cu0.2Zn0.4Fe2O4 nano-spinel ferrites (NSFs). The structural, magnetic, spectroscopic and optic properties have been studied in details. All products have been synthesized via ultrasonic approach via Qsonica ultrasonic homogenizer, frequency: 20 kHz and power: 70 W for 60 min. No annealing or calcination process was applied for any product. The microstructural analysis of products has been done via X-ray powder diffractometry (XRD) which presented the cubic spinel structure with nanosized distribution of all. The cubic morphology of all products were confirmed by both HR-TEM and FE-SEM. Optical band gap (Eg) values were assessed by applying %DR (percent diffuse reflectance) analysis and Kubelka-Munk theory. The Tauc schemes showed that Eg values are in a narrow range (1.87-1.98 eV). The quadrupole splitting, line width, hyperfine magnetic field, isomer shift values and cation distribution have been determined from 57Fe Mossbauer analysis. The magnetic properties of various nanoparticles have been obtained from VSM (vibration sample magnetometer) measurements at 10 and 300 K (RT). The magnetic results revealed superparamagnetic and soft ferromagnetic traits at 10 and 300 K, respectively. Ms (saturation magnetization) and Mr (remanence) initially increase with increasing Tb3+ substituting level up to x = 0.06 then diminish for further x values. Hc (coercivity) shows an opposite variation tendency of Ms and Mr. The observed magnetic traits are deeply discussed in relation with the structure, morphology, magnetic moments and cation distributions.

Ca2+/Mg2+ co-substituted strontium nanohexaferrites: magnetic investigation and Mossbauer analysis

We report a comprehensive evaluation of the microstructures, magnetic, and hyperfine traits of Ca2+/Mg2+ co-substituted strontium nanohexaferrites (SHFs) of chemical compositions Sr1–2xCaxMgxFe12O19 (x ≤ 0.1). These SHFs were prepared using sol–gel unified auto-combustion strategy and characterized by diverse analytical measurements to determine the effects of Ca2+/Mg2+ co-substitution on the aforesaid properties. XRD and high resolution transmission electron microscpe (HRTEM) analyses confirmed the nucleation of HF nanocrystallites. UV-visible diffuse reflectance (DR–UV–Vis) spectra were used to evaluate the optical band gap of the proposed SHFs, which was reduced with the increase in co-substitution contents. The 57Fe Mossbauer spectra was exploited to assess the quadrupole splitting, spectral line-width variation, isomer shift, distribution of cations (Ca2+ and Mg2+), and hyperfine magnetic fields. Measured magnetic parameters such as saturation magnetization, remanence, squareness ratio (SQR), coercivity, and magnetic moment were significantly improved due to the Ca2+/Mg2+ co-substitution. All the prepared SHFs revealed ferrimagnetic nature both at 10 and 300 K. Achieved SQR values ≈0.5 of the studied SHFs clearly disclosed their single domain character possessing uniaxial anisotropy.

Selenite sorption onto goethite: isotherm and ion-competitive studies, and effect of pH on sorption kinetics

Sorption of oxyanions onto ferric oxyhydroxides’ surfaces is naturally occurring process with advantageous implications in remediation of contaminated waters or management of landfills. Therefore, this paper provides information on selenite sorption onto goethite, which is one of the most common oxyhydroxides in the environment. Our results showed that selenite sorption was well described by the pseudo-second-order kinetic model, as well as by Langmuir isotherm. This suggests chemisorption as a rate-controlling step and formation of selenite monolayer on goethite surface with relatively high 83.8 µmol g−1 maximum sorption capacity at pH 3, which was determined for initial selenite concentration in the range of 45–550 µmol L−1 in 0.5 g L−1 (m/v) goethite suspension. The Mossbauer analysis revealed only marginal structural changes in goethite during sorption. Our results also showed that pH significantly affects the overall sorption rate constant with the highest values at the acidic region. Study on competitive sorption behaviour highlighted significant influence of phosphate on selenite sorption. There was no competition for sorption positions with excessive concentrations of sulphate and chloride ions. However, equimolar concentrations of sulphate and chloride led to changes in selenite sorption efficiency. Our results showed that selenite sorption onto goethite is a viable method for selenite removal and, thus, goethite can be successfully applied as a component in commercial composite sorbents or in geochemical barriers.

Valorization of coal treatment residues as a host matrix of nanosized nickel, copper and zinc ferrites

High quality activated carbon was prepared using by-products from the pyrolysis of low rank coals as a precursor. The obtained carbon material was applied as a host matrix of nanosized MFe2O4 ferrites (M = Ni, Cu or Zn). XRD, Mossbauer and TPR analyses were performed for samples characterization and their catalytic behavior in methanol decomposition as a source of hydrogen was tested. In contrast to the reference mesoporous KIT-6 silica based analogues, the active phase in the carbon modifications was more accessible for the reactants and represented a complex mixture of metals, alloys, substituted magnetite and finely dispersed ferrites, which ensured their higher catalytic activity in methanol decomposition.

X-ray photoelectron spectroscopy and low temperature Mössbauer study of Ce3+ substituted MnFe2O4

Spinel Mn2+ Fe 2−x 3+ Ce x 3+ O4 (where x = 0.01–0.05) polycrystalline nanoparticles were fabricated by solution combustion method using glucose and urea as fuels. X-ray diffractogram (XRD) proved the witness of the cubic crystal consort of products which have the crystallite sizes in between 12 and 8 nm. The size of the sample was accomplished via transmission electron microscopy. The elemental composition of iron and manganese ions valences of MnCexFe2−xO4 samples were analyzed by X-ray photoelectron spectroscopy. XPS data reveals iron in all samples was trivalent; manganese was divalent, although tetravalent manganese ions were present on the surface of particles. Magnetic characterization of samples was done via Mossbauer spectroscopy at room temperature and at low temperatures (15 K). The Mossbauer analysis determines the consequence of Ce3+ substitution on isomer shift and quadrupole splitting of all samples. The low temperature Mossbauer spectroscopy results indicate that the presence of Ce3+ ions in the octahedron sites causes the decrease in the concentration of Fe3+ ions.

Structural and magnetic characterization of the Nd2Fe14B + 10%wt.Fe system subjected to high-energy milling

We have investigated exchange-spring magnets made from powders prepared by high-energy milling Nd2Fe14B mixed with 10%wt. Fe, milled for 6 h in a planetary mill, varying the rotation velocity and the starting grain refinement of the soft phase. The samples were characterized by X-ray diffraction, magnetization techniques and 57Fe Mossbauer spectroscopy. The diffractometric and Mossbauer analyses revealed that the Nd2Fe14B compound was partially decomposed in the milling process, increasing the amount of free iron and reducing the grain size of both. Indicative for the Fe2B and Nd1-eFe4B4 phase separation was also found. The magnetization versus applied magnetic field curves showed that both the remanence and coercive field for the 500 rpm milled samples reached values higher than those earlier obtained for un-milled or similarly milled single Nd2Fe14B. However, milling with 600 rpm showed to be deleterious to the same magnetic parameters. It was also demonstrated that milling using iron with less refined grains is more effective to improve the magnetic properties of the composite system.

Antiferromagnetic ordering in lithium deintercalated Fe1−xZnxPO4: A Mössbauer spectroscopy study

Abstract Various compositions of Fe1−xZnxPO4 (x = 0.1, 0.2, 0.3, and 0.5) were synthesized by solid-state reaction and chemical lithium deintercalation processes, and their magnetic properties were characterized based on Mossbauer analysis. The synthesized Fe1−xZnxPO4 have orthorhombic structures with space group Pnma. The magnetization curves of Fe1−xZnxPO4 show the antiferromagnetic behaviors and magnetic phase transition caused by the strong crystal field in the FeO6 octahedral sites. The Neel temperature (TN) of Fe1−xZnxPO4 for x = 0.1, 0.2, 0.3, and 0.5 was found to be 97, 82, 63, and 62 K, respectively. Mossbauer spectra below TN appeared to have eight Lorentzian lines with antiferromagnetic ordering. The charge state of Fe ions is the high spin state of Fe3+, as characterized by an isomer shift (δ = 0.28–0.43 mm/s). The value of magnetic hyperfine field (Hhf) decreased with increasing Zn concentration because the superexchange interaction via Fe–O–Zn link is weaker than that via Fe–O–Fe link. Also, the value of electric quadrupole splitting (ΔEQ) gradually decreased with increasing Zn concentration due to the substitution of a Zn ion for the Fe ion, inducing a change in the charge asymmetry at the FeO6 sites. The Debye temperatures are found to decrease with increasing Zn concentration.

Impact of excess and disordered Sn sites on Cu2ZnSnS4 absorber material and device performance: A 119Sn Mössbauer study

Abstract Mossbauer analysis is carried out on CZTS samples, subjected to a low temperature processing at 300 °C (S1) and high temperature processing at 550 °C under sulfur environment (S2). Loss of Sn is observed in sample S2 due to high temperature thermal treatment. The isomer shifts obtained in the Mossbauer spectra confirms the existence of Sn at its 4 + valence state in both the samples. Relatively high quadriple splitting value is observed in S1 with respect to S2, suggesting dislocations and crystal distortion present in S1, which are reduced drastically by high temperature annealed S2 sample. The fabricated solar cell with S1 and S2 absorbers showed significant improvement in efficiency from ∼0.145% to ∼1%. The presence of excess Sn in S1 allows enhanced recombination and the diode ideality factor shows larger value of 4.23 compared to 2.17 in case of S2. The experiments also validate the fact that S1 with Sn rich configuration shows lower acceptor carrier concentration as compared to S2 because of enhanced compensating defects in S1.

Innovative synthesis and properties of Fe doped nanocrystalline strontium zirconate for the development of visible light driven photocatalyst

Abstract Studies on the band gap engineering for photocatalysis and photovoltaic applications in SrZrO3 (SZO) being not explored. Here, we demonstrated a modified solid state reaction technique to prepare nanocrystalline perovskite with formula SrZr0.9Fe0.1O2.955 (SZFO). Phase analysis by X-ray powder diffractometry revealed the formation of only one orthorhombic phase with smaller crystallite size and enhanced lattice strain as Fe substitutes at Zr site. The availability of SZFO under study for the development of visible light driven photocatalysts was examined through diffused reflectance measurements. For the first time, a shift of the absorption edge to longer wavelength (red region) was observed. A narrowing of the optical band gap (Eg) to its half value (2.23 eV against 4.4 eV for pure sample) was achieved by Fe doping. Light absorbance was also found to drastically increase covering the UV-red region. These changes arose due to the distribution of Fe localized states at the O2p band edge and inside the forbidden gap. The effect of Fe incorporation was also examined by Raman and Mossbauer spectroscopies. Raman studies confirmed the presence of disorder and compositional fluctuations as Fe substitutes at the Zr site. Mossbauer analysis proved the presence of abundant Fe3+ (90%) and few Fe4+ species with distorted octahedral sites. The resultant oxygen deficiency balancing the charge neutrality was calculated. The detected ferromagnetic character was attributed to both super exchange and double exchange interactions. Works are in progress for further tuning of the band gap in SZFO as a promising material for photocatalytic and photovoltaic applications.