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A methodical study on structural, electrical and dielectric properties of NiFeCoO4 nanoparticles, synthesized via sol-gel technique has been reported in this article. X-ray diffractogram confirmed phase purity of the synthesized sample. Raman spectra show the five predicted Raman bands that appear around 600–720, 250–360, 500–590, 450–520 and 180–220 cm−1 corresponding to A1g, Eg, T2g (3), T2g (2) and T2g (1), respectively. From the dielectric measurements, we have determined the different dielectric parameters such as the conductivity σac, complex permittivity e*, complex impedance Z*, and the tangent loss (tanδ). The electrical properties strongly depend on temperature and frequency. The relaxation activation energy deduced from the Z” vs. frequency plots was similar to the conduction activation energy obtained from the conductivity. Hence, the same type of charge carriers are attributed to the relaxation process and the conduction mechanism. The complex impedance plots have revealed the presence of only one semicircular arc corresponding to grains and grain boundaries contributions at all the temperatures and an equivalent electric circuit was proposed as a model of the sample.

The cobaltite spinel MnCo2O4 nanopowder was prepared by the sol–gel method. X-ray diffraction shows the pure compound that crystallized in the cubic structure with the Fd $$\stackrel{-}{3}$$ m space group. The infrared spectrum (IR) revealed two absorption peaks that can be attributed to Mn–O and Co–O vibrations in the octahedral and tetrahedral sites, respectively. The electrical and dielectric studies were characterized by impedance spectroscopy (IS) at different frequencies (40–106Hz) and temperatures (200–440K). As a matter of fact, the DC conductivity exhibits a semiconductor behavior. It is worth mentioning that the conductivity of our investigated cobaltite spinel was found to be σ = 6.10−3 Sm−1 at room temperature. These results allowed this material to be a good candidate for potential application as an anode material (fuel cell). The AC conductivity obeys the Jonscher's law at low temperatures T 340K. Moreover, the dielectric result shows the permittivity (e '≈ 103) which is due to the contribution of the Maxwell–Wagner polarization.

This work involves the synthesis and study of physical properties of the La0.8Ca0.1Pb0.1Fe0.975Mg0.025O3 compound, which has been characterized by various experimental techniques, such as X-ray diffraction, SEM and complex impedance spectroscopy. The structural study showed that the La0.8Ca0.1Pb0.1Fe0.975Mg0.025O3 compound crystallized in the orthorhombic structure with the Pnma space group. The particle size and the surface morphology of this compound have been analysed using SEM. The particle size was found to be around 120 nm and we confirmed that one particle contains more than one crystallite. Importantly, the studied compound presented a giant dielectric permittivity (e′ of around 9 × 104 at high temperature and low frequencies). An equivalent electric circuit has been deduced from the Nyquist plots of the complex impedance parts (Z′′ vs. Z′) to correctly describe the electrical behavior of the La0.8Ca0.1Pb0.1Fe0.975Mg0.025O3 compound. The chosen circuit consists of two cells mounted in series corresponding to the grain and grain boundary contributions. The electrode contribution has been detected from the frequency dependence of the imaginary part of modulus where the activation energy of each constitution has been calculated. The relaxation process and the electrical conductivity are attributed to the same type of charge carriers characterized by similar values of the activation energy determined from loss factor tangent (tg(δ)), the imaginary part of the permittivity and the modulus spectrum.

The hexaferrite Ba1−xSrxFe12O19 compounds with x = 0, 0.5 and 1 were synthesized by the autocombustion method. X-ray diffraction (XRD), Raman spectroscopy and transmission electron microscopy (TEM) were used for structural and morphological studies.

La1−2xBaxBixFeO3 (0.00 ≤ x ≤ 0.20) nanoparticles were prepared by the auto-combustion method using glycine as a combustion fuel. X-ray diffractometry (XRD) measurements confirmed the orthorhombic structure of the synthesized compounds with the Pnma space group as a principal majority phase and showed the presence of a very minor secondary phase when x > 0.1. The nanosize criterion of the prepared compounds was confirmed from the crystallite size values calculated using the Williamson–Hall formalism. The relaxation process has been studied by the frequency dependence of the imaginary parts of impedance and modulus (Z′′ and M′′) which satisfied the Arrhenius law. Nyquist plots allowed us to obtain an adequate equivalent circuit involving the grains and grain boundary contributions. The activation energies calculated from Z′′, M′′ and the resistance of both contributions deduced from the Nyquist plots are found to be very similar. The conduction mechanism has been analyzed using the temperature dependence of the exponent Jonscher's power law parameter which confirms the NSPT conduction mechanism type for all compounds with an enhancement of the binding energy of the charge carrier (WH) with the substitution.

In the present investigation, La0.75Ba0.10Sr0.15FeO2.875-δ oxygen-deficient ferrites with δ = 0.00, 0.125 and 0.25 were synthesized by sol–gel method. The physical characterization has been carried out by X-ray diffraction, scanning electron microscope SEM, Raman spectroscopy, and complex impedance. All samples are formed in orthorhombic crystal symmetry with Pnma space group. Synthesized compounds have nanocrystallite size of 32–46 nm. Raman spectrum shows the oxygen vacancy effect on the tilt and stretching phonon modes. Electric properties were investigated in the framework of impedance and electric conductivity. The complex impedance was measured over a wide range of temperatures (300–380 K) and frequencies (40 Hz–1 MHz). The electrical measurements indicate semiconductor behavior for the three compositions and emphasize the evidence of contribution of grain boundaries in the transport properties. The ac conductivity curves obey the Jonsher universal power law and are assigned to hopping conduction mechanism. It is found that the values of activation energy, estimated from the conductivity analysis, are in the same order with those deduced from relaxation process. Such result proves that both processes, conduction and relaxation, are related to the same defect.

The La0.8Ba0.1Ce0.1FeO3 compounds were prepared by the auto-combustion route and annealed at two different temperatures to study their effect on the structural, morphological and dielectric properties of the Barium- and Cerium-substituted LaFeO3 compound. The X-ray diffraction analysis revealed that both compounds crystallized in the orthorhombic structure belonging to the Pnma space group. The rise of the annealing temperature from 700 to 900 °C was found to lead to the increase of the average grain size value as characterized by SEM. Furthermore, two clear relaxations phenomena have been detected using the Nyquist and Argand’s plots of dielectric impedance and Modulus curves at different temperatures, which are attributed to both grain and grain boundary contributions. Their activation energies have been calculated not only from the frequency dependence of both imaginary parts of impedance (Z″) and modulus (M″) but also from the contribution of the resistances deduced from the Nyquist plots. These plots have been adjusted using two circuits in series, each of which containing a resistance in parallel to a CEP capacitance. The conduction mechanism was analyzed by ac conduction using the Jonscher’s power law. The NSPT conduction model has been confirmed for both compounds in which the rise in heat treatment decreases the binding energy of carriers.

The aim of this research work was to study the structural and magnetic properties of iron oxide nanoparticles. The as-prepared sample was synthesized by a co-precipitation route and annealed at different temperatures. The annealed samples were investigated using different techniques such as X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), vibrating sample magnetometry (VSM), and Mossbauer spectrometry (MS). The XRD results indicate the formation of three phases which have been identified as magnetite (Fe3O4), maghemite (γ-Fe2O3), and hematite (a-Fe2O3). The crystallite size was very similar for both magnetite and maghemite, and it was higher for hematite. The TEM observations showed that the particle shapes were affected by the annealing temperature (Tan). In addition, the SEM analysis revealed a wide distribution of the particle size. The magnetic measurements enabled the determination of a blocking temperature for both Fe3O4 and γ-Fe2O3 as 210 and 240 K, respectively. The Morin transition temperature was determined in the case of α-Fe2O3 from the magnetization and the MS measurements. The synthesized iron oxide nanoparticles can be good candidates for hyperthermia applications.

In this work we investigate the effect of Ag+ doping at Sr2+ site in La0.57Nd0.1Sr0.33−xAgxMnO3 (LNSAMOx, x = 0.00 and 0.15) system on the magnetic and magneto-electrical properties. The variation of the magnetization M versus temperature T, at 0.05 T, reveals a ferromagnetic–paramagnetic transition for all samples. All samples undergo a sharp metal–semiconductor transition at a temperature Tρ, accompanying the ferromagnetic–paramagnetic transition. The maximum values of resistivity temperature coefficient (TCR) and magneto-resistance were 2.5% K−1 and 63% at room temperature of 290 K and 305 K, respectively. The TCR value is considered as an important factor in determining the sensitivity of uncooled infrared bolometers. Most interesting is that the adjustment of the low-temperature range ρ–T revealed the presence of low-temperature peaks in the resistivity curves, attributed to the diffusion effects of grain boundaries, electron–electrons, electron–magnon, electron–phonons and the interactions between them. Overall, LNSAMOx polycrystalline ceramics appear promising for uncooled infrared detectors, magnetic memories or magnetic storage devices.

We report on structural, magnetic properties of Na-doped La0.8Sr0.15Na0.05MnO3 (LSNMO) nanoparticles (NP) with size about 50 nm elaborated via sol-gel route. The chemical composition was verified using the energy dispersive X-ray analysis (EDAX) and by X-ray photoelectron spectroscopy (XPS). Magnetic characterizations demonstrate that LSMNO exhibits a coexistence of interacting superparamagnetic (ISPM) phase with blocking temperature T-B = 194 K and a ferromagnetic phase with Curie temperature T-C = 255.5 K. At low temperatures, the SPM state undergoes a collective freezing state at T-f = 46 K. the high-temperature regime (well above TC) reveals that NP-LSNMO has a strengthened Griffiths-like phase compared to their bulk counterpart. An itemized investigation of the critical behavior of the material was carried out in the vicinity of T-C. The critical exponents [beta = 0.546(7), gamma = 0.972(6), and delta = 2.94 (5)] were found to be in close agreement with of the mean-field theory. The maximum magnetic entropy change (-Delta(pk)(M)) is about 1.41 Jkg(-1) K-1 and the refrigeration capacity (RC) is 288 Jkg(-1) for a field change of 5 T at T = 215 K. This magnetocaloric response is reasonably high for nanomaterials and, together with its cost-effectiveness, makes NP LSMNO a potential candidate material for active magnetic refrigerators. Besides, the ISPM properties are desirable for hyperthermia applications. Our findings suggest that the magnetic inhomogeneity and the dipolar interaction between the SPM and FM phases in the range T-B < T < T-C are crucial factors in determining the magnetic properties of NP-LSNMO. (C) 2021 Elsevier B.V. All rights reserved. Portuguese Foundation for Science and Technology European Commission QREN-Mais Centro Project Deanship Scientific Research at Jouf University central laboratory at Jouf University

Two compounds with the formula La0.8Ba0.1Bi0.1FeO3 have been prepared by the sol–gel (LBBFO-SG) and the auto-combustion (LBBFO-AC) preparation methods. The effect of the preparation method on structural, morphology, vibrational, electrical, and dielectric properties have been carried out using the X-ray diffraction (XRD), Scanning electron microscopy (SEM), and Raman and impedance spectroscopy. The Rietveld refinement of the XRD diffractograms confirms the crystallization of both compounds through the Pnma space group. Furthermore, the nano-size scale of the prepared compounds was verified by the XRD and the SEM microscopy. From the Raman study, we conclude that the vibration modes are similar to those of the pure LaFeO3 with a slight shape change in some modes. The relaxation processes were analyzed with the Bergmann formalism to validate the presence of two relaxation processes corresponding to grains and boundary grains contributions. These relaxations have been confirmed by studying the dielectric constant also the dielectric loss tangent is used to study the ferroelectric–paraelectric phase transition at around room temperature. The activation energy for both contributions has been calculated from the impedance, the modulus, and the dielectric loss tangent and they have almost the same values. The Nyquist plots (Z″ vs. Z′) have been adjusted using two circuits in series containing each one a resistance in parallel to a CEP capacitance.

The perovskite (La0.8Ca0.2)1−xBixFeO3 (x = 0.00, 0.05, 0.10, 0.15 and 0.20) LCBFO compounds were synthesized by the sol–gel method using the citric acid route and sintered at 800 °C (LCBFO800) and 900 °C (LCBFO900). The structural properties studied by X-ray diffraction (XRD) revealed that all the compounds present the same crystallographic structure confirmed by the superposition of all the characteristic peaks. The slight deviation of the XRD peaks towards the weakest angles informed us that the volume of the elementary mesh increases as a function of the rate of substitution (bismuth). This observation, which is obviously valid for the two series, confirmed that the annealing temperature has no influence on the structure. Scanning electron microscopy (SEM) micrographs showed that the morphology of the samples is characterized by the presence of large agglomerates. Although, transmission electron microscopy (TEM) characterization confirmed the nano-sized grains. These two characterization techniques revealed that the LCBFO800 series presents the smallest grain size. The magnetic study exposed that all the samples (LCBFO800 and LCBFO900) show a weak ferromagnetic behavior (unsaturated hysteresis curves) and an increase in magnetization (M) with increasing Bi-content, with a higher M value for a lower annealing temperature. The Curie temperature is smaller in the case of LCBFO800 compounds and decreases with the insertion of Bi.

In this study, our central focus is to investigate the magnetocaloric characteristics of a La1−x□xMnO3 (x = 0.1, 0.2 and 0.3) series prepared by a sol–gel technique published in Prog. Mater. Sci., 93, 2018, 112–232. The crystallographic study revealed that our compounds crystallize in a rhombohedral structure with Rc. Ferromagnetic (FM) and paramagnetic (PM) characters were detected from the variation in magnetization as a function of magnetic fields at different temperatures. The second order transition was verified from the Arrott plots (M2 vs. (μ0H/M)), where the slopes have a positive value. In order to verify the second order, we traced the variation of magnetization vs. temperature at different magnetic fields for x = 0.2. This revealed a ferromagnetic (FM)–paramagnetic (PM) transition when temperature increases. Relying on the indirect method while using the Maxwell formula, we determined the variation in the entropy (−ΔSM) as a function of temperature for different magnetic fields for the three samples. We note that all the studied systems stand as good candidates for magnetic refrigeration with relative cooling power (RCP) values of around 131.4, 83.38 and 57.26 J kg−1 with magnetic fields below 2 T, respectively. Subsequently, the magnetocaloric effect was investigated by a phenomenological model for x = 0.2. The extracted data confirm that this phenomenological model is appropriate for the prediction of magnetocaloric properties. The study also demonstrated that this La0.8□0.2MnO3 system exhibits a universal behaviour.

In this study, the FePt core, ZnIn2S4 shell and FePt-ZnIn2S4 core-shell nanostructures were successfully synthesized using solvothermal process. Temperature dependent hysteresis behavior of as-synthesized nanoparticles (NPs) FePt and FePt/ZnIn2S4 showed super paramagnetic response at 300 K and ferromagnetic properties with a coercive field (Hc) of 2830 Oe and 970 Oe at 2 K, respectively. Also, the blocking temperature (TB) estimating by the peak in ZFC curves was about 26 K for FePt and about 46 K for FePt/ZnIn2S4 NPs. After the identification process of nanostructure, using electrochemical methods, the behavior of FePt-ZnIn2S4 core-shell@PGE was studied in 0.1 M phosphate buffer solution (PBS) containing 5.0 mM [Fe(CN)6]3−/4−. The EIS complex plane plots showed a drastic change in the charge transfer resistance of the probe redox reaction as a function of UO22+ concentration. This behavior was used for construction of the calibration curve, and a linear range from 0.5 to 10.0 μM UO22+ with a detection limit of 71.7 nM. Keywords: Core-shell nanostructures, Solvothermal process, Magnetization behavior, Uranyl glue, Electrochemical study

(La0.8Ca0.2)1−xBixFeO3 (x = 0.00, 0.05, 0.10, 0.15 and 0.20) (LCBFO) multiferroic compounds have been prepared by the sol–gel method and calcined at 800 °C. X-ray diffraction results have shown that all samples crystallise in the orthorhombic structure with the Pnma space group. Electrical and dielectric characterizations of the synthesized materials have been performed using complex impedance spectroscopy techniques in the frequency range from 100 Hz to 1 MHz and in a temperature range from 170 to 300 K. The ac-conductivity spectra have been analysed using Jonscher's power law σ(ω) = σdc + Aωs, where the power law exponent (s) increases with the temperature. The imaginary part of the complex impedance (Z′′) was found to be frequency dependent and shows relaxation peaks that move towards higher frequencies with the increase of the temperature. The relaxation activation energy deduced from the Z′′ vs. frequency plots was similar to the conduction activation energy obtained from the conductivity. Hence, the relaxation process and the conduction mechanism may be attributed to the same type of charge carriers. The Nyquist plots (Z′′ vs. Z′) at different temperatures revealed the appearance of two semi-circular arcs corresponding to grain and grain boundary contributions.

In this study, a Cu1.5Mn1.5O4 spinel was successfully synthesized by a sol–gel method at 500 °C for 5 h and characterized by different techniques. X-ray diffraction (XRD), Fourier transformation infrared (FTIR) spectroscopy and Raman spectroscopic analyses confirmed the formation of a spinel cubic structure with the Fdm space group. The SEM proves that the grain size of our compound is of the order of 48 nm. Crystallite sizes determined from three estimates are closer to the grain size obtained from the SEM, indicating the single domain nature of the sample. The optical properties of UV-visible spectroscopy for our sample showed that the gap value is equal to 3.82 eV, making our compound a good candidate for optoelectronic applications. For electrical properties, impedance spectroscopy was performed at a frequency range of 40 ≤ frequency ≤ 106 Hz. This suggested hoping conduction due to three theoretical models. The latter can be attributed to the correlated barrier hopping (CBH) model in region I, overlapping large polaron tunneling (OLPT) in region II and non-overlapping small polaron tunneling (NSPT) mechanism in region III. One dielectric relaxation is detected from the dielectric impedance and modulus, attributed to grain contributions. This behavior was confirmed by both Nyquist and Argand's plots of dielectric impedance at different measuring temperatures.

In this paper, we present the effect of lanthanum (La) and sodium (Na) vacancies in site A on the morphological, structural, magnetic, and electrical properties of La0,8-x□xNa0,2-x□xMnO3 compounds with x = 0.00, x = 0.05, and x = 0.075 prepared with the sol–gel method. The results of the X-ray powder diffraction diagrams show that these samples crystallize in a rhombohedral structure deformed with the space group R$$ \overline{3} $$c, while electron microscopy was carried out for the surface morphology. From the magnetic measurements, the transition from a ferromagnetic (FM) state to a paramagnetic (PM) state in the vicinity of Curie temperature TC is detailed. Moreover, in the electrical part, we study the gap effect on the transition temperature TMI; thus, the nature of the charge transport for the resistance behavior in the different regions (low temperature, metallic, and insulating) has been explained by different models. This work is completed by explaining the two types of magnetoresistance (MR) observed as a function of temperature and applied magnetic field: low-temperature extrinsic magnetoresistance (EMR) and high-temperature intrinsic magnetoresistance (IMR) have been found to be conserved (≈ 30 ℅) with decreasing precursor percentage at room temperature.

Superparamagnetic iron oxide nanoparticles (SPIONs) were synthesized in this work, featuring uncommonly high magnetization saturation values at room temperature for coated nanoparticles. They also show very low cytotoxicity and promising protein loading efficacy. The ratios of iron(III) acetylacetonate (precursor), benzyl ether (solvent) and oleylamine (surfactant) were changed relatively to those used in the thermal decomposition protocols reported in the literature, in order to enhance the magnetic response of the nanoparticles to an external magnet. The SPIONs were fully characterized in terms of their chemical composition, iron oxide phases, grain/particle sizes and magnetic behaviour. They are predominantly constituted by magnetite, with minor maghemite contributions, as observed by Mossbauer spectroscopy and X-ray diffraction data. The magnetization saturation at room temperature of the best SPIONs achieved 68 emu g−1, which is relevant considering that it corresponds to ∼10 nm sized nanoparticles, where interactions have some significance. This characteristic is mainly due to the high content of magnetite (93% of iron sites) in the nanoparticles and low aggregation provided by their organic coating. In addition, Field-Cooled and Zero Field-Cooled curves allowed to confirm, from the blocking and irreversibility temperatures, the nanoparticle size distribution broadening obtained by Transmission Electron Microscopy. The test of cytotoxicity of the best SPIONs shows very encouraging results for clinical applications, with a half maximal inhibitory (cell viability reduction) concentration (IC50) value as high as 759 μg/mL. Bovine serum albumin protein was loaded on these SPIONs, and very good loading efficacy and capacity of SPIONs for lower concentration of protein was observed, both in water and acetate buffer (pH 5.0), representing these results a successful proof-of-concept for forthcoming studies with therapeutic proteins.

The local structure of SrFe12O19 nanoparticles was investigated by a combined synchrotron pair distribution function (PDF), Raman and 57Fe-Mossbauer spectroscopic analysis. The PDF and 57Fe-Mossbauer spectroscopy results indicate that SrFe12O19 nanoparticles exist in an M-type hexagonal phase (∼10 nm), with a dynamically disordered trigonal bipyramidal Fe(2) site (2b). We determine that at 300 K, the timescale dynamics of Fe3+ ions near the 2b positions are between 10−15 and 10− s. The Raman spectra show anomalous shifts in all active phonon wavenumbers above TN ≈ 720 K, indicating the presence of spin-phonon coupling. The Fe3+(2b) dynamic regime motion was interpreted by taking into account changes in the electric polarization at T = TN, which discontinuously drops to zero at this temperature.

In this study, La0.67Ca0.2Ba0.13Fe1−xCrxO3 (x = 0 and 0.03) powders were prepared by auto-combustion method. The examination of the purity and crystalline structure of the samples by X-ray diffraction showed a cubic structure formed with the $$Pm\overline{3}m$$ space group. Scanning electron microscopy was used to study the morphology and grains size, indicating an agglomeration of nanometric particles. Impedance spectroscopy in the temperature range from 200 to 360 K was used in order to understand the evolution of the electrical behavior of the substituted perovskites. The real and imaginary parts of the impedance were adjusted with two different equivalent circuits. The activation energies extracted from the imaginary part of the impedance, and the electrical conductivity was very closed indicating a transformation of the electrical behavior. This was confirmed by a decrease in the resistance after substitution of Fe cations by Cr ones. AC conductivity studies showed a Jonscher’s behavior and a change of conduction process from a succession of NSPT and CBH model to the existence of only CBH one after the substitution.

The topotactic reduction of La0.75Ba0.10Sr0.15FeO2.875 with titanium metal leads to a new isostructural material of the composition La0.75Ba0.10Sr0.15FeO2.875−δ (δ = 0.375 and 0.50). XRD analysis of phases confirms that the obtained compound adopts a brownmillerite-type structure. A slight distorted monoclinic P2/m was found to describe the crystal structure. The transport properties have been investigated by current–voltage (I–V). The electric and dielectric measurements were carried out covering a wide range of temperature (300–600 K). Our materials display semiconducting properties as well as mixed ionic and electronic conductivity. At high temperatures, the activation energy values proved to be around 907 − 630 meV, which refers basically to oxygen vacancies conduction. The analysis of dielectric properties and dielectric losses (ε’, tanδ) of both compounds vs temperature at different frequencies demonstrates two relaxer attitudes. A low dielectric loss and low electrical conductance were displayed. Relying upon these values, these materials stand for perfect candidates for micro-electronics devices.

The physico-chemical properties of lacunar perovskite based materials have been analyzed with the study of the relations between the structure and the effect of defencies. Studies have been conducted on the effect of creating vacancies in lanthanum and sodium for the compound La0.8-x□xNa0.2-x□xMnO3 (x = 0, 0.05, 0.075) obtained by the sol-gel method followed by heat treatment at different temperatures and by X-ray diffraction in the surface. The magnetization measurements M (H, T), which were carried out using a magnetometer, proved that all studied compounds exhibited a second order reaction. The importance of -ΔSM induced by the weak magnetic field, introduce that the materials can be used for practical applications. Magnetic entropy change (ΔSM) values estimated by Landau theory and Hamad theory are close to those obtained using the classic Maxwell relation. The most important result is that our compound possesses relatively high values of magnetic entropy variation (ΔSM) and refrigeration capacity (RCP) which makes them promising candidates for magnetic refrigeration.

Made available in DSpace on 2021-06-25T10:25:53Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-05-16 Iron mining residues were successfully used in the fast and inexpensive sol-gel synthesis of magnetic hybrids (CoFe2O4/NOM), with water rich in natural organic matter (NOM) as solvent. XRD analyses revealed formation of the cobalt ferrite phase, while SEM and TEM images showed the formation of nanostructures. The hybrids obtained (HbSF and HbLM) provided excellent rates of conversion (99%) of nitrophenol in short times of 50 and 120 s, respectively. The hybrids also showed high performance in the adsorption of PAHs, achieving removals of 75–88% (HbSF) and 72–81% (HbLM). This work contributes to the conversion of industrial operations from linear to cyclic processes. Chemistry Department Federal University of Sergipe (UFS) Department of Physics Federal University of Sergipe (UFS) Federal Institute of Education Science and Technology of Sergipe University of Coimbra CFisUC Physics Department Institute of Chemistry UNESP National Institute of Alternative Technologies for Detection Toxicological Evaluation and Removal of Micropollutants and Radioactive Materials (INCT-DATREM), P.O. Box 355 Institute of Chemistry UNESP National Institute of Alternative Technologies for Detection Toxicological Evaluation and Removal of Micropollutants and Radioactive Materials (INCT-DATREM), P.O. Box 355

The magnetic properties, Mossbauer and the critical behavior of the compound Bi0.8Ba0.1Er0.1Fe0.96Cr0.02Co0.02O3 prepared by sol-gel are the subject of this study. The compound has an R3c structure and exhibits a ferromagnetic to paramagnetic phase transition c.a. 574 K. A theoretical adjustment of the hysteresis cycles at room temperature show two magnetic contributions: Ferromagnetic (FM) and Antiferromagnetic (AFM) with a predominance of the first contribution. Mossbauer spectroscopy revealed two Fe3+ cations differently coordinated. Magnetic measurements versus magnetic field reveal that the sample exhibits a second order magnetic phase transition. The Curie temperature ​​and the critical exponents (β, γ and δ) were determined by different techniques. These values are in agreement with the ones predicted by the mean field model.

The La0.67Ca0.2Ba0.13Fe1−xMnxO3 perovskite compounds with different manganese concentrations (x = 0.0, 0.03, 0.06) were synthesized by the autocombustion method and annealed at 700 °C. The X-ray diffraction (XRD) data indicated that all obtained compounds crystallize in the cubic structure with the Pm $$\overline{3}$$ m space group. The increase in the substitution rate has been found to lead to the decrease in the crystallite size value characterized by X-ray diffraction. The dielectric properties of these samples, using a complex impedance spectroscopy technique, were also performed as a function of frequency and temperature. A suitable equivalent electrical circuit was used to assess the contributions of electrode, grains, and grain boundaries in the complex impedance results. Activation energies were determined from different methods. Nyquist plots were consistent with three circuits in series, each one with a capacitance in parallel with a resistance. The conduction mechanism follows the NSPT model for the three samples at T

Perovskite-type oxides La1-xBixNi0.5Ti0.5O3 (x = 0.0, 0.2) were prepared by the sol–gel method employing the citric acid route and sintered at 820° C. The structural behavior analyzed by X-ray diffraction proved that all the samples have the same crystallographic structure (space group Pnma). The volume of the elemental lattice decreases with the rate of Bismuth substitution. Transmission electron microscopy (TEM) verified the nanosized grains. The FTIR spectra confirmed the formation of the orthorhombic perovskite structure. UV–Visible spectroscopy and photoluminescence were also applied to study the samples. The parameters of real and imaginary part of dielectric function (e′ and e″) and dielectric loss tangent (tg(δ)) show a strong frequency dependence. Those dependences explain a dispersive behavior at low frequencies and are outlined on the basis of the Maxwell–Wagner model and Koop theory. The compounds have very high dielectric constant values (e′ ≈ 103) that are useful in electronic devices. Electric modulus formalism was employed to investigate the relaxation dynamics of charge carriers. Moreover, a non-Debye type of relaxation was verified in our samples. The activation energy is specified from the analysis of the imaginary part of the electric modulus.

We have investigated the effect of multi-doping in A and B site of the multiferroic prepared by the Sol-gel method Bi0.8Er0.1Ba0.1Fe0.96Co0.02Cr0.02O3 (BEBFCC) on the structural, morphological and electric properties. X-Ray diffraction and Rietveld refinement confirm that the BEBFCC compound presents a rhombohedral structure with the R3C space group. The Ac electrical properties have been measured from 331 to 735 K as a function of frequency (100 kHz - 1 MHz). Debye's theory and Arrhenius relations were used to study the relaxation phenomenon. The frequency dependence of the impedance (Z”: imaginary part) reveals the existence of one relaxation peak, while the Modulus formalism shows two peaks. The presence of two contributions, related to the dielectric relaxations visible in this compound, was confirmed by the Impedance Nyquist plots. The study of the ac conductivity based on Jonsher's power law confirms that the conduction is associated to the Non-Overlapping Small Polaron Tunneling model.

We applied a general non-aqueous route for the formation of mono-, bi-, tri-, tetra, hexapod and multipod magnetic spinel ferrite metal oxide (CoFe2O4) nanocrystals. The magnetic CoFe2O4 nanocrystals were characterized by X-ray diffraction, high-resolution transmission electron microscopy, Raman spectroscopy, magnetometry and Mossbauer spectroscopy, to understand their structure and magnetic properties. These CoFe2O4 nanoparticles have the smallest particle size reported ever, with a mean diameter of ∼3 nm. The coercivity was found to be larger compared to that reported in the literature for spherical particles. Mossbauer spectroscopy indicated a magnetic transition above room temperature, where 20% of the Fe ions transit to a paramagnetic state, around 400 K. From the thermal dependence of magnetic parameters, the blocking temperature was estimated to be around 425 K. These studies indicate that our CoFe2O4 nanocrystals are different from their cubic/spherical counterparts, which generally display a single domain character. These CoFe2O4 nanocrystals display a strong shape anisotropy dependent magnetic property.

Ni0.5Zn0.5FeCoO4 spinel ferrite was elaborated using sol-gel technique. X-ray diffraction patterns indicate that sample has a cubic spinel type structure with Fd-3m space group. The change in Raman modes and relative intensity were observed due to ball milling and consequently to the decrease of particle size and cationic redistribution. The Raman spectra show peaks appearing at 450 and 490 cm−1 corresponding to T2g (2) and T2g (3), respectively. It may be noted that both of these modes shift toward the higher wavenumber with the substitution of Zn by Ni in Ni0.5Zn0.5FeCoO4 ferrite. Mossbauer spectroscopy analysis shows one tetrahedral A-site and two octahedral B-sites. Due to Zn doping, the hyperfine magnetic fields are much smaller than for CoFe2O4 and NiFe2O4 ferrites. The Jonscher’s power low was used to describe the ac-conductivity measurements. Frequency dependence of dielectric constant (e″) and tangent loss (tan) display a dispersive behavior at low frequencies that can be explained by the Maxwell Wagner model and Koop's theory. Electric modulus formalism has used to study the relaxation dynamics of charge carriers. The complex impedance spectra (Nyquist plots) show well-defined semicircles which are strongly dependent on the temperature.

(La0.8Ca0.2)1−xBixFeO3 (x = 0.0, 0.1, and 0.2) compounds were prepared by the sol-gel method, using the citric acid route. Structural and microstructural characteristics of the samples were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy. Mossbauer spectroscopy was also used for magnetic characterization and structural confirmation of X-ray data. Refinement of XRD patterns indicated that the compounds crystallize in an orthorhombic structure, Pnma space group. The SEM measurements showed that the morphology of the samples is characterized by the existence of large agglomerates, while TEM confirmed the fine particle size. Raman spectra revealed that, when increasing temperature, the level of oxygen species adsorbed at the surface of the particles increases progressively. Room temperature Mossbauer spectroscopy data revealed the existence of two octahedral magnetic sites in the structure of the compounds, which is compatible with XRD data, and a small percentage of a paramagnetic phase in the samples, which increases with Bi-content.

A new mixed-valence ironIII-zincII diphosphate, Zn2+Fe3+2(P2O7)2, has been prepared by a dry way and characterized structurally by several techniques. Analysis of the powder diffraction pattern of the synthesized diphosphate showed that it is isostructural with the ironIII-ironII diphosphate, Fe2+Fe3+2(P2O7)2, crystallizing in an orthorhombic symmetry in the Pnma space group. Other physical properties were characterized using Mossbauer spectroscopy and Vibrating Sample Magnetometer measurements, which showed that this new phosphate with Fe3+ ions in VI coordination has a paramagnetic behavior at room temperature. Infrared and Raman spectroscopies were also used in this study to help characterizing structurally the new synthesized material.

Structural studies of Zn2+Fe $_{2}^{3+}$ (P2O7)2 and Cu0.5Zn0.5Fe2(P2O7)2 were made using powder X-ray diffraction and refined by Rietveld method. Both phosphates crystallize in an orthorhombic structure with Pnma space group. Magnetometry measurements showed that below TN = 5.6 (1), Zn2+Fe $_{2}^{3+}$ (P2O7)2 becomes antiferromagnetic and the TN = 14 K is attributed to Cu0.5Zn0.5Fe2(P2O7)2. Mossbauer studies at room temperature and low temperature were performed in both samples.

A new valence-mixed iron(III)-zinc(II)-copper(II) pyrophosphate, Cu2+0.5 Zn2+0.5 Fe3+2 (P2O74−)2, has been synthesized by a dry-way method and structurally characterized by several techniques. The powder diffraction pattern of the new material shows that the pyrophosphate is isostructural with the iron(III)-iron(II) pyrophosphate Fe2+Fe3+2 (P2O74−)2, crystallizing in an orthorhombic arrangement in the Pnma space group. Cu2+Fe3+2 (P2O74−)2 was formed as a secondary phase, as determined both by X-ray diffraction and Mossbauer spectroscopy. Mossbauer spectroscopy and magnetometry measurements showed that Cu0.5Zn0.5Fe2(P2O7)2 is paramagnetic at room temperature and the iron ions are in octahedral coordination. Neel temperature is about 3 K. Infrared and Raman spectroscopies were also used in this study to characterize the new pyrophosphate.

In the present study, Nd0.7Sr0.3NbO3–y (y = 0.1, 0.15, 0.2) compounds were prepared via a solid–solid reaction route. The prepared samples were characterized by electrochemical impedance spectroscopy in order to establish the effects of temperature, frequency, and oxygen vacancies on both the transport and dielectric properties of NdSrNbO. We found that both the electrical and dielectric properties were highly sensitive to the concentration of oxygen vacancies. The conduction mechanism data were explained well according to the Mott model and adiabatic small polaronic hopping model. Electrochemical impedance spectroscopy analysis showed that one relaxation process was present in the Nd0.7Sr0.3NbO2.9 system whereas two relaxation processes were observed in the Nd0.7Sr0.3NbO2.85 and Nd0.7Sr0.3NbO2.8 systems, where the latter behavior indicated the presence of many active regions (due to the contributions of different microstructures). The temperature and frequency dependences of the dielectric constant confirmed the contributions of different polarization mechanisms. In particular, the high dielectric constant values at low frequencies and high temperatures were mainly related to the presence of different Schottky barriers, whereas the low dielectric constant values at high frequencies were essentially related to the intrinsic effect. The constant dielectric values obtained for the samples are greater than those in the NdSrFeO system, which makes them interesting materials for use in applications that require high dielectric constants.

In the present paper, the La1–2xBaxBixFeO3 (x = 0.00, 0.05, 0.10, 0.15 and 0.20) nanosized perovskite materials have been successfully prepared by the auto-combustion route using the glycine as fuel. The structural, morphological, and gas sensing properties of these samples have been investigated. The Rietveld refinement has revealed a single orthorhombic phase (Pnma space group) for the compounds with x ≤ 0.10, while the samples with x = 0.10 and 0.20 have been found to contain a minor amount of two secondary phases. We have confirmed that the La0.8Ba0.1Bi0.1FeO3 (x = 0.10) compound possesses the smallest average particle size (34.58 nm) with the purely orthorhombic structure and exhibits a high surface roughness, as determined by atomic force microscopy measurements. Importantly, the gas sensing tests have been carried out for all prepared compounds with different ethanol and H2S gas concentrations (from 5 to 100 ppm). The La0.8Ba0.1Bi0.1FeO3 (x = 0.10) compound has been proven to exhibit excellent performance in ethanol and H2S gas response even for very low concentrations (5 ppm) with an optimum operating temperature of 180 and 200 °C, respectively. Furthermore, the response and recovery times analyzed for both these gases were found to be very short (between 5 and 10 s).

This work aims to obtain multifunctional nanocomplexes with a superparamagnetic core and an upconversion luminescent shell, by synthesizing superparamagnetic iron oxide nanoparticles (SPIONs) functionalized with lanthanide ions. These materials may be used in numerous applications, e.g. in the biomedical and environmental fields. Three distinct nanocomplexes were synthesized: SPIONs@LaF3:Yb3+/Er3+, SPIONs@NaYF4:Yb3+/Er3+ and SPIONs@NaYF4:Yb3+/Ho3+. The first was obtained using the microemulsion and co-precipitation methods and the latter using the thermal decomposition method. A heat treatment was also applied to the SPIONs@LaF3:Yb3+/Er3+ nanocomplex. VSM revealed the superparamagnetic character of the nanocomplexes, and the saturation magnetization was 10.2emu·g−1, 8.4emu·g−1, 8.3emu·g−1 and 14.0emu·g−1 for SPIONs@LaF3:Yb3+/Er3+ without and with heat treatment, SPIONs@NaYF4:Yb3+/Er3+ and SPIONs@NaYF4:Yb3+/Ho3+ nanocomplexes, respectively. The upconversion process in these materials was confirmed by multiphoton microscopy. For SPIONs@NaYF4:Yb3+/Er3+, three peaks of emission were obtained, at 520nm, 540nm and 657nm, while for SPIONs@NaYF4:Yb3+/Ho3+ and SPIONs@LaF3:Yb3+/Er3+ samples only two peaks were observed, at 540nm and 647nm for the first, and at 540nm and 657nm for the latter. The results for the nanocomplex which uses Ho3+ ions as activators are very promising, since similar nanocomplexes are yet to be reported and good magnetic and luminescent properties were achieved. Keywords: Fluorescence, Upconversion, Superparamagnetism, Lanthanides, Nanocomplexes, Iron oxide

The effect of Bi doping of (La0.8Ca0.2)1-xBixFeO3 perovskites on structural and magnetic properties was investigated. X-ray diffraction, magnetometry and Mossbauer spectroscopy measurements were performed on the samples. The sol gel prepared samples were annealed at 800 °C, 900 °C and 1200 °C. The samples crystallize in an orthorhombic structure with a PNMA space group. The LCBFO800 samples have Mossbauer spectra with large sextets in accordance with the small grain size. The several spectral components observed in the sample series are in accordance with the ones found in literature. Hyperfine magnetic fields decrease slightly with Bi content and increase with annealing temperature. Isomer shifts and quadrupole splitting stay constant with composition and annealing temperature. Magnetometry measurements show that the antiferromagnetic behavior is dominate over the ferromagnetic one. Bi doping increases coercivity and decreases remanent magnetization, while annealing temperature increases coercivity and remanent magnetization.

The present study focusses on a stony meteorite found in the 90’s in North West Africa, that has not yet been classified. It was studied by optical microscopy, X-ray fluorescence, X-ray diffraction and Mossbauer spectroscopy. The Fe-bearing phases found by Mossbauer spectroscopy are consistent with the elements found by XRF measurements as well as with phases determined by XRD patterns. The RT spectrum is complex mainly due to the large linewidths of the lorentzians or to the distribution of sites that can obscure the presence of sextets or doublets. From the results obtained the classification of the NWAXX meteorite can be made to an achondrite Winonaite.

In this research paper, our central focus is upon structural, optic, magnetic, magnetocaloric, and critical phenomena of La0.57Nd0.1Sr0.18Ag0.15MnO3 (LNSMAO) compound. This compound is crystallized in the rhombohedric system, with a $$R\mathop 3\limits^{ - } c$$ space group. The band gap energy of this powder was 2.5 eV. Therefore, the LNSAMO sample proved to be not only a photocatalysis material but also a photovoltaic application. The FTIR spectra confirmed the formation of the structure of orthorhombic perovskite. The second-order transition of the magnetic phase in the LNSMAO sample was also reported by the positive slopes of the Arrott plot. Beneath 5 T, the values of magnetic entropy change and relative cooling power, respectively, amounted to about 5.08 J kg−1 K−1 and 146.7 J/Kg. In perspective, this sample stands for an agreeable candidate for magnetic refrigeration. By analyzing the dependence on the field of the magnetic entropy change (ΔSM) data as well as the relative cooling power (RCP), it was possible to assess the values of the critical exponents. Moreover, the critical exponents of LNSMAO compound were estimated based on multiple techniques like Kouvel-Fisher (KF), modified Arrott plot (MAP) method, and critical isotherm analysis (CIA). The reliability of these critical behaviors was verified by the Widom scaling relation and the universal scaling hypothesis. Our results demonstrate an excellent correlation between magnetocaloric effect (MCE) properties in manganese systems and critical behavior.

The effect of induced crystallization on changes in electrical transport of two types of glass‐ceramics, pure polaron conductive 40Fe2O3‐60P2O5 (F40) (mol%) and predominantly polaronic 5Li2O‐5ZnO‐40P2O5‐ 50WO3 (Li‐50W) (mol%) was investigated. F40 glass‐ceramics produced at low heat‐treatment temperatures contain single‐phase Fe3(P2O7)2 whereas at higher temperatures two more phases Fe4(P2O7)3 and Fe(PO3)3 are formed. Structural modifications strongly depend on the crystallization temperature and time. The appearance of crystalline phases studied by Mössbauer spectroscopy exhibits changes in Fe2+/Fetot ratio in crystalline/glassy phases. The detailed analysis of different iron sites allows their correlation with changes in electrical conductivity as crystallization progresses. Depending on the course of crystallization, the contribution of each phase to the overall conductivity is determined by the frequency dependence of Zʺ(ω) and Mʺ(ω). DC conductivity shows a sharp decrease as Fe3(P2O7)2 phase appears and consequently glass matrix remains impoverished in Fe2+‐Fe3+ pairs. In the multiphase systems prepared at higher crystallization temperatures, the overall electrical conductivity increases although the continuous grain boundaries along different crystalline grains play a limiting factor. In contrast, the slight conductivity change in Li‐ 50W glass‐ceramics upon crystallization is a result of remaining W5+‐W6+ pairs in the residual glassy phase. Independence of electrical transport on Li+ ions confirms predominantly polaronic transport in Li‐50W glass‐ceramics.

In this work, we employed the Laser Floating Zone (LFZ) method to grow the ceramic fibers with composition of 50Fe2O3-50SiO2 and 90Fe2O3-10SiO2, with two different pulling rates: 25 and 200 mm/h. The physical properties of the ceramics were studied as the function of the iron oxide content and the pulling rate. XRD analysis depicted that the main crystalline phase formed in all samples is magnetite. Although, the appearance of small quantity of nano-crystalline fayalite was also confimed. From the magnetic measurements, a Verwey transition for all LFZ fibers in the temperature range varying from 100 to 115 K depending on the composition and the pulling rate, was observed. Room temperature 57-Fe Mossbauer measurements showed that the degree of non-stoichiometry of LFZ ceramics with 90% of the iron content is higher than one for LFZ samples containing 50% of iron oxide. A great agreement was obtained between the result of Mossbauer spectroscopy measurements and VSM studies. The revealed behaviours can be described in terms of the temperature dependent interactions occurring between the magnetic clusters formed in the fibres.

Airborne environmental particles (EP) more commonly referred as particulate matter (PM) are an illustrative marker of air pollution that is associated with adverse effects on human health. Considering, PM is a complex mixture, not only in terms of its chemical composition, but also in the range of particle size, it is difficult to identify which attribute contributes more for the toxicity. Currently, there is no report about the immunotoxicological effects caused by PM with reduced content of heavy metals. This study intends to address this gap and provides a detailed characterization and immunotoxicity evaluation of PM collected in an urban area with heavy traffic congestion. Environmental particles were separated by different sizes though a sucrose gradient. This method allowed to achieve 4 sized fractions: EP f 15 % with a mean diameter of 284 nm ± 1.86 nm, EP f 25 % with a mean diameter of 461 nm ± 1.72 nm, EP f 35 % with a mean diameter of 1845 nm ± 251 nm and EP f 45 % with a mean diameter of 2204 nm ± 310 nm. Only the fractions with the smallest sizes (EP f 15 % and EP f 25 %) were subsequently studied. The chemical composition of both fractions was not substantially different, and the dominant elements were C, O, Ca and K. Only EP f 25 % showed to have a small amount of Fe. Therefore, the heavy metal elements were eliminated through centrifugation. Essentially, we found that the EP f 15 % was more cytotoxic in RAW 264.7 cells than EP f 25 %, which indicates the smaller size as the motive for the higher toxicity. In addition, both fractions of EP presented a good internalization in macrophages after 2 h exposure and induced the production of reactive oxygen species in a concentration-dependent manner. Moreover, EP f 15 % and EP f 25 % led to a strong secretion of proinflammatory cytokines (TNF-α and IL-6) in human peripheral blood mononuclear cells (hPBMCs) in the 3 concentrations tested. The inflammatory response observed was independent of the presence of heavy metals and endotoxins, since these last were suppressed by using polymyxin B sulfate. This report emphasizes the importance of an adequate physicochemical characterization and adequate controls in the experiments to achieve a right interpretation of the biological effects caused by PM.

The (La 0.8 Ca 0.2 ) 0.9 Bi 0.1 FeO 3 (LCBFO) compound has been synthesized by the sol-gel method and characterized by X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), Raman spectroscopy and electrical impedance spectrometry . XRD results revealed that (La 0.8 Ca 0.2 ) 0.9 Bi 0.1 FeO 3 crystals are orthorhombic, belonging to the Pnma space group. The SEM measurements showed that the sample presents a large distribution of nano-grains connected to each other. The relaxation process and the electrical conductivity are awarded to the same type of charge carriers characterized by similar values of the activation energy determined from loss factor tangent t g δ , the imaginary part of the permittivity and from the Modulus spectrum. The ac -conductivity was analysed to examine the conduction mechanism, using the Jonscher’s universal power-law given by: σ ac ω = σ dc + A ω s . Based on the parameter s behavior, the conductivity was studied according to the NSPT model (non-overlapping small polaron tunneling).

A new mixed-valence diphosphate, Zn2+5Fe3+2(P2O7)4, was synthesized from FeII5FeIII2(P2O7)4 via the “solid way” route, by substitution of FeII by ZnII. The obtained X-ray data confirmed the crystallization of the compound in the C2221 symmetry space group (orthorhombic). Magnetic measurements were performed showing that, at room temperature, the compound is paramagnetic and that the Neel temperature is 15.44(20) K. The compound was also investigated by infrared and Raman spectroscopies, in particular to characterize the (P2O7)4− and M–O vibrations.

Two nanoparticle orthoferrite materials (La0.8Ca0.2)0.9Bi0.1Fe1−yTiyO3 (y = 0.0 and 0.1) have been successfully synthesized via the assisted ball milling solid-state reaction. The effect of Bismuth and Titanium ions insertion in A and B-sites of La0.8Ca0.2FeO3 material on structural, dielectric relaxation and magnetic properties was conducted. Structural study reveals the formation of majoritarian orthorhombic phase in both nanomaterials. Importantly, both compounds present a giant dielectric constant e’ and low dielectric loss tangent tg(δ). Two relaxation processes have been detected at low and high-temperature ranges. The adjustment of the imaginary parts of complex Modulus via the Havriliak-Negami formalism (H-N) confirms a Cole-Cole (grains) and Cole-Davison (grain boundaries) relaxation processes at low and high temperature regions, respectively. The magnetic study reveals the enhancement of magnetization when introducing Titanium ions in B-site which increases the Ferromagnetic interactions. It also confirms an important decrease in the Curie Weis temperature (TC = 450 K).

This article reports on a detailed study of the structural, spectroscopic and magnetic properties of La0.57Nd0.10Sr0.18Ag0.15FeO3 (LNSAFO) ferrite nanoparticles, which were prepared using the solid state technique. The Rietveld analysis of the powder X-ray diffractograms indicated that the material crystalizes in an orthorhombic structure, Pnma space group. Scanning electron microscopy (SEM) measurements showed that all particles have almost spherical shapes, and are characterized by a distribution of relatively narrow particle sizes. The average diameter of the particles was estimated within the 25–45 nm range by three different methods (SEM, and from the XRD data using the Debye-Scherer and Williamson–Hall models).The elemental composition of the synthesized material has been investigated by energy dispersive spectroscopy (EDS), which confirmed the presence of all expected elements in stoichiometries matching those of the precursor oxides of the synthesized perovskite. Raman spectroscopy measurements revealed that the studied sample had a considerable degree of crystallinity, in agreement with the X-ray diffraction data. Finally, the magnetic properties of the studied compound have been investigated by studying the variation of the magnetization as a function of temperature in both the ZFC (zero field cooled) and FC (field cooled) modes. A blocking temperature (TB) of around 100 K was observed.

This review presents studies on iron meteorites (Campo del Cielo fall and an unregistered iron meteorite), an unregistered stony meteorite from Northwest Africa, and 13 tektites from the American, European, and Australasian strewn fields. The main experimental technique used in the studies was Mössbauer spectroscopy, both in transmission and backscattering geometries. For the latter, a MIMOS II spectrometer was used. Additionally, optical and scanning electron microscopies and X-ray diffraction were used. In the studied iron meteorites, kamacite is found as the main mineral. Campo del Cielo meteorite exhibits Widmanstätten patterns and schreibersite inclusions. The unregistered iron meteorite has Neumann lines and schreibersite inclusions. We have assigned Campo del Cielo as an octahedrite and the unregistered iron meteorite as a hexahedrite. The unregistered stony meteorite is composed mainly of iron-free silicates; at 4.2 K, the spectrum indicates maghemite and 1% troilite. The Cambodian tektite appeared individualized from other australasites, unlike the moldavite, which tends to cluster with them. Our analyses do not allow dismissing doubts on the provenance of tibetanites. The Fe3+/Fe2+ ratio was found to be higher for Muong Nong-type tektites than for splash-form tektites, as expected from their morphology and solidification from melt at lower temperature.

A streamlined synthesis approach is proposed to develop a multifunctional magnetite doped hybrid silica aerogel by taking advantage of the versatility of the sol-gel process and flexibility of the crosslinking reaction. To this avail, magnetite NPs, at concentrations from 0.05 to 0.2 mg/mL, were mixed at the nanoscale with the initial solution containing the silica precursors and the crosslinker. For an effective and sustainable linkage of magnetite to the silica network, the surface of the magnetite was chemically coated with an active silylation agent to compatibilize the surface chemistry of these nanoparticles with the chemistry of silica. It has been shown that at a certain dopant concentration, the magnetite doped aerogels gained several interesting improvements in the final properties over their undoped counterparts, particularly an increase in the compressive strength (up to 2.6 MPa, with ca. 3× increase) with only a marginal increase in the density (up to ∼ 0.29 g cm−3, with 20% increment) and decrease in the active surface area (down to ∼ 49 m2 g−1 and 7% reduction). Importantly, a good deal of improvement regarding the thermal insulation performance for doped aerogels has been obtained due to the opacification behavior of the magnetite dopants at temperatures above 300 K. The significant improvements concerning the physical and mechanical properties combined with the magnetic properties (up to 11 emu g−1 at room temperature) make these multifunctional hybrid aerogels suitable for some applications, ranging from selective magnetic separation for environmental cleaning and magnetic drug delivery to catalysis, etc.

Mesoporous silica nanoparticles with a superparamagnetic iron oxide core were prepared in this work, in order to obtain multifunctional platforms with adequate features for cancer theranostics. Three different core-shell nanocomplexes were obtained: IO-OAm/mSiO2, IO-APTES/mSiO2 and IO/SiO2/mSiO2. In the case of IO-OAm/mSiO2 and IO-APTES/mSiO2, iron oxide (IO) was obtained by thermal decomposition, having in this case a coating of oleylamine (OAm) that was in the second formulation exchanged by (3-aminopropyl)triethoxysilane ligand (APTES). Regarding the IO/SiO2/mSiO2 formulation, iron oxide was synthesized by microemulsion. The mesoporous silica shell (mSiO2) on the IO nanoparticles was obtained by sol-gel and the final materials were dried by supercritical fluids drying. VSM confirmed the superparamagnetic behaviour of the nanoparticles, leading to MS of 4.0, 1.8 and 10.2 emu·g−1, for IO-OAm/mSiO2, IO-APTES/mSiO2 and IO/SiO2/mSiO2, respectively. NMR relaxometry has shown the potential of these nanoparticles to be used as T2 contrast agents, with r2 values as high as 63.93 s−1·mM−1 Fe. The three types of nanoparticles exhibited loading contents of epirubicin of ~3% and drug release percentages of 19% for IO-OAm/mSiO2, 24% for IO-APTES/mSiO2 and 31% for IO/SiO2/mSiO2. The cytotoxicity of drug-loaded and non-loaded most promising nanoparticles was assessed, showing high potential of these platforms for application as anticancer drug carriers.