The Co0.5Ni0.5CexSmyFe2-x-yO4 (CNCSF) XRD pattern revealed the purity of the samples without any secondary phase. The crystallite size CNCSF are in nano range. Further, the calculated lattice ...parameter of CNCSF are found to increasing with the RE content. From SEM micrographs surface morphology and the microstructure of the CNCSF was studied. The porous nature of the samples is revealed by SEM, which will aid in increasing their sensing response. Energy dispersive X-ray spectroscopy (EDS) patterns have confirmed the stoichiometric presence of Co2+ Ni2+, Ce3+, Sm3+ and Fe3+, those are used to prepare the CNCSF. The dielectric behaviour is similar to that of conventional spinel ferrite structures, in that the dielectric constant is highest at low frequencies and decreases at higher frequencies due to electron hopping, resulting in dielectric dispersion. Only one semicircle is seen in each Cole-Cole plot, which has uncovered that the contribution to conductivity is predominantly from the grain boundaries. At room temperature, the gas sensing responses of CNCSF thin films were investigated. For liquified petroleum gas (LPG), the gas sensing characteristics of the prepared thin films were investigated. At room temperature, the x = 0.03 thin films showed excellent sensitivity to liquified petroleum gas. The sensing response and recovery time of all of the thin films that had been prepared were reported. The sensing response of x = 0.03 thin films was highly stable over a period of 60 days on exposure to LPG (1000 PPMv), according to the stability analysis. The sample thin film with x = 0.03 can be utilized in gas sensor technology, particularly for the detection of LPG at room temperature, due to its increased sensitivity, quick response and recovery times, and stability.
Pictorial representation of the material deposited on the gas substrate and gas sensing setup, SEM micrographs, The gas response in x,y = 0.0 to x,y = 0.03 thin film samples on exposure of different concentration of LPG on complete gasification and degasification process. Display omitted
•LPG gas sensing characteristics of the Co0.5Ni0.5CexSmyFe2-x-yO4 were investigated for the first time.•The sensing response of x = 0.03 sample is stable over a period of 60 days on exposure of LPG (1000 PPMv).•The sample x = 0.03 can be utilized in the detection of LPG at room temperature.•The dielectric constant is highest at low frequencies due to electron hopping.
Abstract
X-ray absorption near-edge structure (XANES) spectra are the fingerprint of the local atomic and electronic structures around the absorbing atom. However, the quantitative analysis of these ...spectra is not straightforward. Even with the most recent advances in this area, for a given spectrum, it is not clear a priori which structural parameters can be refined and how uncertainties should be estimated. Here, we present an alternative concept for the analysis of XANES spectra, which is based on machine learning algorithms and establishes the relationship between intuitive descriptors of spectra, such as edge position, intensities, positions, and curvatures of minima and maxima on the one hand, and those related to the local atomic and electronic structure which are the coordination numbers, bond distances and angles and oxidation state on the other hand. This approach overcoms the problem of the systematic difference between theoretical and experimental spectra. Furthermore, the numerical relations can be expressed in analytical formulas providing a simple and fast tool to extract structural parameters based on the spectral shape. The methodology was successfully applied to experimental data for the multicomponent Fe:SiO
2
system and reference iron compounds, demonstrating the high prediction quality for both the theoretical validation sets and experimental data.
Results of studies of the structure, microstructure, dielectric characteristics and the Mössbauer effect of solid solutions of the (1-x)PbFe1/2Nb1/2O3 - xPbFe2/3W1/3O3 system in wide temperature ...range are presented. X-Ray diffraction and Mössbauer spectra showed that in the PbFe1/2Nb1/2O3 there are regions with a high and low concentration of Fe3+ ions - clustering; in PbFe2/3W1/3O3 there is a process of local ordering of cations in the B-sublattice. The number of local states of Fe3+ ions indicates the occurrence of partial ordering of ions in the B-position in the system (1-x)PbFe1/2Nb1/2O3 - xPbFe2/3W1/3O3. As x concentration increases, a nearly linear increase in the N é el temperature was observed. Investigation of ceramic cleavage surfaces allows us to conclude that the grain structure and the dependence of the grain size on the amount of the PbFe2/3W1/3O3 are inhomogeneous. It is shown that additional maxima in the dependence of the imaginary part of relative complex permittivity appearing above the phase transition temperature are associated with the onset of hopping conduction.
•The solid solutions of the (1-x)PbFe1/2Nb1/2O3 - xPbFe2/3W1/3O3 system were produced.•The partial ordering of ions Fe3+ in the B-position in the system (1-x)PbFe1/2Nb1/2O3 - xPbFe2/3W1/3O3 was found.•The dependence of the grain size on the amount of the PbFe2/3W1/3O3 was demonstrated.•The hopping conduction in the solid solutions of the (1-x)PbFe1/2Nb1/2O3 - xPbFe2/3W1/3O3 system was found at analysis of the permittivity.
The HoFeO3 and HoFe0.8Sc0.2O3 nanoparticle samples were prepared by the solution combustion method using a mixture of fuels as carbamide and glucose. Their structural, electronic and magnetic ...properties are studied. The XRD study confirmed that the samples were single-phased and had Pbnm orthorhombic structure. The partial substitutions of Fe3+ ions by the Sc3+ ions with larger ionic radii resulted in the growth of lattice parameters. The surface morphology of the samples was examined by the scanning electron microscopy. The XPS data confirmed that both iron and scandium in the samples are trivalent. However, holmium was found to be trivalent only in the sample with a nominal composition HoFeO3. The data processing for the sample with a nominal composition of HoFe0.8Sc0.2O3 indicated that holmium ions were in Ho2+ and Ho3+ states with the ratio of 0.45/0.55. The Mössbauer study showed that iron ions in both samples were in Fe3+ state. About 10% of Fe3+ ions in HoFe0.8Sc0.2O3 were found to be in local environment with the coordination number 4. Collecting Mössbauer spectra in the temperature range of 14–723K allowed estimating magnetic phase transition temperatures (TM) for HoFeO3 and HoFe0.8Sc0.2O3 nanoparticle samples. TM values are 640K for HoFeO3 and 385K for HoFe0.8Sc0.2O3.
•HoFeO3 and HoFe0.8Sc0.2O3 ceramic samples are synthesized by solution explosion method.•HoFe0.8Sc0.2O3 sample contains Ho2+and Ho3+ions; Ho2 +/Ho3+= 0.45/0.55•Physical model is proposed to explain the ionic state of Ho in HoFeO3 and HoFe0.8Sc0.2O3.•Some of the Fe3+ions in HoFe0.8 Sc0.2O3 have tetrahedral anions environment.•Magnetic phase transition temperatures are 640K for HoFeO3, and 385K for HoFe0.8Sc0.2O3.
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•The average crystallite size from Scherrer formula is 25nm.•The RT Mössbauer results suggest the existence of some local disorder in the arrangement of cations in the ...sub-lattice.•The Sm3+doping reduce the temperature of magnetic phase transitions and magnetic hyperfine field vales of Fe3+.
For the first time, we report on the low temperature Mössbauer spectroscopic study of Zn2+0.5Mn2+0.5Sm3+xFe3+2−xO4 (where x=0.01–0.05) prepared by the modified solution combustion method using a mixture of urea and glucose as a fuel. The Mössbauer spectroscopy at room and low temperatures was applied to understand the magnetic properties of the samples. The room temperature Mössbauer spectroscopy results suggest that the occupation of the octahedral sites by Sm3+ ions leads to the distortion enhancement of 57Fe nuclei environments, which leads to an increase in quadrupole splitting Δ values of D2 and D3 doublets. The low temperature Mössbauer spectroscopy results indicate that the presence of Sm3+ ions in the octahedron sites causes the decrease in the number of Fe–O–Fe chains. The transformation of Mössbauer spectra doublets into Zeeman sextets is accompanied by a significant decrease in the magnitude IM of Mössbauer spectra intensity within the 0–1.2mm/s velocity range normalized to its value at 300K. This drop in the temperature dependence of IM allows one to obtain the magnetic phase transition temperature TM from the Mössbauer experiment.
Spinel Mn
2+
Fe
2−x
3+
Ce
x
3+
O
4
(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 MnCe
x
Fe
2−x
O
4
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 Mössbauer spectroscopy at room temperature and at low temperatures (15 K). The Mössbauer analysis determines the consequence of Ce
3+
substitution on isomer shift and quadrupole splitting of all samples. The low temperature Mössbauer spectroscopy results indicate that the presence of Ce
3+
ions in the octahedron sites causes the decrease in the concentration of Fe
3+
ions.
•BaFe1/2Sn1/2O3-δ was obtained using the sol-gel method and additional O2 treatment.•Oxygen treatment increases Fe4+ content from 27% to 36%.•The absorption band is strongly broadened and shifted to ...the visible and IR regions.•Oxygen treatment results in significant increase of conductivity.•BaFe1/2Sn1/2O3-δ exhibits giant dielectric response in a wide frequency range.
Barium ferrostannate BaFe1/2Sn1/2O3-δ was obtained using the sol-gel precursor method and additional annealing in O2. Phase purity of ceramics was confirmed by x-ray diffraction, the microstructure and microanalysis of grains were investigated by scanning electron microscopy methods, whereas the valence states and coordination of tin and iron ions were determined using Mössbauer spectroscopy. We found out that as-sintered and O2-treated samples contain 27% and 36% of six-coordinated Fe4+ ions, respectively, whereas Fe3+ ions are five-coordinated. Oxygen treatment results in a decrease of the average sizes of coherent scattering regions, increase of the local distortion of SnO6 octahedra, and significant increase of conductivity. Experiments on diffuse reflection show that the characteristic absorption band is strongly broadened and shifted to the visible and IR regions, which is explained by the formation of a large number of local donor levels in the band gap. Thus, the optical band gap is reduced by Fe-doping as compared to BaSnO3 and can be additionally adjusted by annealing in oxygen. Both as-sintered and O2-treated BaFe1/2Sn1/2O3-δ ceramics exhibit giant dielectric response in a wide frequency range.
We report on the structure, spin-lattice and magneto-electric coupling in (1−x)Pb(Fe2/3W1/3)O3-(x)BiFeO3(where x = 0.1 and 0.4) (PBFW) solid solution synthesized through two-step solid-state reaction ...method. The room temperature (RT) crystallographic studies were carried out using x-ray diffraction and neutron diffraction measurements which show a single-phase Pseudocubic crystal system with Pm-3m space group. Rietveld refinement was carried out to obtain the structural parameters using Fullprof software and the observed structural parameters are in good agreement with the previous reports. Temperature-dependent neutron diffraction measurements reveal the presence of commensurate G-type antiferromagnetic structure. The magnetic structure was analyzed using the propagation wave vector k ∼ (½ ½ ½) for both the solid solutions. The obtained lattice constants increase linearly and the magnetic moment decrease with temperature, which shows a remarkable anomaly around the magnetic (TN ∼ 405 K for x = 0.1 and 531 K for x = 0.4) transition temperatures. This anomaly clearly indicates the existence of spin-lattice and magnetoelectric coupling. The magnetic susceptibility (ZFC and FC at 500 Oe) and M-H hysteresis loop measurements show spontaneous magnetic moment due to the Fe3+-O2−-Fe3+ superexchange interaction coexisting with the weak ferromagnetism. Bifurcation of ZFC and FC curve reveals the strong anisotropic nature. Astonishingly, magnetic measurements show the non-zero magnetic moment above TN and broadening of the magnetic transition indicates the presence of short-range uncompensated sublattice weak ferromagnetic clusters in the paramagnetic region. The Mossbauer spectroscopy and electron paramagnetic resonance studies exhibit the RT magnetically ordered system and confirm the +3 state of Fe along with the fraction of Fe2+ ions.
A set of Sm-doped iron oxide magnetic nanoparticles (Fe x O y NPs) of different sizes as an example of ferromagnetic NPs at room temperature was synthesized by microware-assisted methods. Powder ...X-ray diffraction and transmission electron microscopy showed Fe x O y NPs with an inverse spinel structure. Mössbauer and X-ray absorption spectroscopy (XAS) were used to study the local atomic and electronic structure of iron in the NPs. Linear combination of XAS spectra of reference iron oxides failed in reproducing the spectra of Fe x O y NPs Piquer, C. ; J. Phys. Chem. C 2014, 118, 1332−1346 . We attribute this fact to the nonstoichiometric distribution of tetrahedral, Td 3+, and octahedral, Oh 3+ and Oh 2+, sites in NPs compared to bulk references. This distribution was successfully reproduced by linear combination of theoretical XAS spectra obtained for clusters where iron was in Td 3+, Oh 3+, and Oh 2+ defined oxidation and symmetry states. This approach allowed us to obtain the quantitative speciation of the fraction of Td 3+, Oh 3+, and Oh 2+ sites as a function of the different size of the Sm-doped Fe x O y NPs based on the XAS data. In contrast to the standard XAS reference compounds analysis where experimental spectra fits are limited to constant Td 3+/Oh 3+ and Td 3+/Oh 3+/Oh 2+ ratios and to Mössbauer spectroscopy that requires liquid helium temperatures, the proposed method opens a new possibility to quantitatively estimate the amount of each independent inequivalent iron site in terms of symmetry and oxidation state at room temperature.
Ferrites are a very common commodity in the modern world due to their very strong magnetic permeability, high resistivity, modest permittivity, high saturation magnetization, low power losses, low ...coercivity, low remanence magnetization, and low power losses. These properties are mainly depending on chemical composition, synthesis method, and other parameter. Further based on these parameter material exhibits noticeable properties. Aiming on these points we have prepared 100% replacement at A site AB
2
O
4
materials with several dopant i.e. Co
2+
, Ni
2+
, Cu
2+
. All the samples were prepared by solution combustion method using glucose as fuel. This method is the only one method very less expensive compare to other synthesis methods. The MFe
2
O
4
(M=Co
2+
, Ni
2+
, Cu
2+
) samples were characterised by XRD and VSM to confirm phase, structure, crystallinity, and magnetic behaviour of the samples. XRD data reveals that crystallite size were found decreases with changing transition metal 100% replacement at A site. Magnetic behaviour was studied by using VSM and results reveals that samples were turns ferrimagnetic to ferromagnetic nature with changing substitution. As a result of sensing study, these samples could be used to develop sensing materials in the future. According to the hysteresis analysis, the desorption mechanism is less than the adsorption process. At room temperature, the humidity sensing material is extremely stable at higher concentrations of Co ferrites. The low sensing response ferrites, on the other hand, have a lot of potential for sensor applications, hence our results help for permanent magnet applications. Since samples exhibits highly porosity so that these samples very good candidates for humidity sensor applications.
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