Electrical and electro-chemical characterisation of La0.99Fe1−x Ni x O3−δ perovskites

(LFN, 0<x<0.6) perovskites were synthesised by a solid-state route and were characterised by powder XRD, dilatometry, four-point DC conductivity measurements and electro-chemical impedance spectroscopy (EIS) on cone-shaped electrodes using a Ce_1.9Gd_0.1O_1.95 (CGO10) electrolyte. All the compounds were of single phase, and they belong to either the cubic or the hexagonal crystal system. The thermal expansion coefficient (TEC) was in the range 10.7*10⁻⁶ K⁻¹ to 13.4*10⁻⁶ K⁻¹, which continued to increase with increasing nickel content. The highest electronic conductivity was measured for the composition giving a value of 670 S/cm at 380 °C. The highest electro-chemical performance was measured for the composition giving an area specific resistance as low as 5.5 Ωcm² at 600 °C based on EIS measurements on a cone-shaped electrode. Composite cathodes made from and CGO10 revealed a rather low performance due to an un-optimised micro-structure.

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Sol–gel synthesis and catalytic property of Ce1−x Ti x O2 nanocomposites supported on attapulgite clay

Ce_1?x Ti _x O₂ nanocomposites supported on attapulgite clay (Ce_1?x Ti _x O₂/ATP) were prepared by a facile sol–gel route. The textural and structural properties of the prepared products were characterized by thermogravimetric-differential scanning calormetry analysis, X-ray diffraction, transmission electron microscopy, energy-dispersive spectrometry, Fourier transform infrared spectroscopy and Nitrogen adsorption-desorption measurements. The catalytic activity of the prepared Ce_1?x Ti _x O₂/ATP catalysts for rhodamine B degradation was investigated. Results indicate that the particle size of Ce_1?x Ti _x O₂ nanoparticles evenly attached onto the surface of ATP is approximately 10 nm. The Ti⁴⁺ doping ratios exhibit considerable impact on the redox ability and catalytic activity of Ce_1?x Ti _x O₂/ATP composites. The introduction of an optimal amount of Ti⁴⁺ contributes to forming structure defects and electronic defects in the oxide lattice, increasing concentration of oxygen vacancies, consequently improving low-temperature redox ability of Ce⁴⁺ and enhancing catalytic activity of the composites. Ce_1?x Ti _x O₂/ATP (x = 0.5) catalyst has the best catalytic degradation efficiency, which can reach as high as 97 % after reaction for 240 min. It is also found that attapulgite clay exhibit a positive synergistic effect to the Ce_1?x Ti _x O₂ nanoparticles.     

Characterization of superparamagnetic Mg x Zn1−x Fe2O4 powders

Structural and magnetic properties of Mg _x Zn_1−x Fe₂O₄ powders have been studied with respect to the application for thermal cancer therapy (magnetic hyperthermia). Mg _x Zn_1−x Fe₂O₄ (x=0.1–0.5) powders with particle sizes between 5 and 8 nm were produced by citrate method. The X-ray diffraction patterns of the samples correspond to a spinel phase. The lattice constant and the volume of the elementary cell increase when x changes from 0.1 to 0.5. The FTIR-spectra ascertain the spinel phase formation. The Mossbauer studies reveal the presence of extremely small particles, which undergo superparamagnetic relaxation at room temperature. The core-shell model has been applied to explain quadruple doublets. The quadruple splitting at “shells” is bigger than those at “cores” whereas the isomer shifts remain close. Magnetic studies confirm the presence of extremely small particles that behave as superparamagnetic ones.      

Ferrimagnetic spinels in hydrothermal and thermal treatment of MnxFe2−2x(OH)6−4x

Products of hydrothermal treatment of the initial amorphous system Mn_xFe_2–2x(OH)_6–4x for 0x1 in 0.1x intervals, and products of their further thermal treatment, were examined by chemical analysis, X-ray, IR, and DTA techniques supported by magnetic measurements. After hydrothermal growth for lowx, hematite and goethite phases occurred. Although the goethite phase was still identifiable atx=0.6, formation of a solid solution with the isostructural groutite was not found. The ferrimagnetic spinel phase, which resists heating up to 400C, was present at 0.5x0.9. At higher temperatures, it transformed into the rhombohedral hematite type phase or into the cubic bixbyite phase. AtT900C, a ferrimagnetic spinel structure reappeared up tox=0.8. For x=0.9, the low- and high-temperature forms of the hausmannite phase occurred, forx= 1 passing from one form into another through Mn₅O₈ and partritgeite.For a primary mixture Mn_0.5Fe(OH)₄, corresponding to the manganese ferrite structure, the lattice parameter of which passes from 8.43 å through 8.33 å to 8.50 å, the probable crystallochemical formula was suggested.We are grateful to KBN (The State Committee for Scientific Research, Poland) for grant No. 3 T09A 064 08, which contributed substantially to the materialization of this project.     

Low-temperature synthesis and characterization of the Mn–Zn ferrite

Nanocrystalline ferrite with the composition: Mn_0.6Zn_0.4Fe₂O₄ was synthesized by two-stage route: the precipitation of Zn, Mn and Fe hydroxides from sulphates solution and the synthesis of a precursor by the sol–gel auto-combustion method. The ferrite powder obtained from the gel by ashing was sintered under air at a temperature of 720, 1150 and 1300 °C. The composition and morphology of the as-obtained phases were examined by ICP-AES, TG/DTA, XRD, FTIR, SEM and low-temperature nitrogen adsorption (BET). It was found that the spinel phase forms after gel combustion. The nanometric ferrite powder obtained as a result of the combustion is soft-agglomerated. The zinc content in the ferrite during ashing and auto-combustion is lower by about 21 mol% than the assumed one and the final product turn out to be Mn_0.68Zn_0.32Fe₂O₄.     

Atoms state and interatomic interactions in perovskite-like oxides: XXXII. Formation of paramagnetic clusters in the La1−0.33x Ca0.33x Fe x Al1−x O3 and La1−0.33x Sr0.33x Fe x Al1−x O3 solid solutions

Calcium- and strontium-containing lanthanum orthoferrites have been studied using magnetic dilution method. It has been shown that the iron-atom clusters with competing ferro- and antiferromagnetic exchange interactions can exist. By using Mossbauer spectroscopy, Fe(IV) atoms have been found in the La_1?0.33x Ca_0.33x Fe_xAl_1?x O₃ solid solutions and Fe(III) atoms in two different surroundings have been found in the La_1?0.33x Sr_0.33x Fe _x Al_1?x O₃ solid solutions. The compositions of paramagnetic clusters stable at the infinite dilution have been proposed basing of the magnetic susceptibility and Mossbauer spectroscopy data.     

Sol–gel synthesis of nanocrystalline Zn1−xNixFe2O4 ceramics and its structural,magnetic and dielectric properties

Zn_1?xNi_xFe₂O₄ (0.0 ≤ x ≤ 1.0) nanoparticles are prepared by sol–gel method using urea as a neutralizing agent. The evaluation of XRD patterns and TEM images indicated fine particle nature. The average crystallite size increased from 10 to 24 nm, whereas lattice parameters and density decreased with increasing Ni content (x). Infrared spectra showed characteristic features of spinel structure along with a strong influence of compositional variation. Magnetic measurements reveal a maximum saturation magnetization for Zn_0.5Ni_0.5Fe₂O₄ (x = 0.5); however, reduced value of magnetization is attributed to the canted spin structure and weakening of Fe³⁺(A)–Fe³⁺(B) interactions at the surface of the nanoparticles. Impedance analysis for different electro-active regions are carried out at room temperature with Ni substitution. The existence of different relaxations associated with grain, grain boundaries and electrode effects are discussed with composition. It is suggested that x = 0.5 is an optimal composition in Zn_1?xNi_xFe₂O₄ system with moderate magnetization, colossal resistivity and high value of dielectric constant at low frequency for their possible usage in field sensor applications.     

Microwave synthesis of sulfur-doped α-Fe2O3 and testing in photodegradation of methyl orange

α-Fe₂O₃, as a promising photocatalyst in environmental aspects, was doped by a nonmetal to enhance the optical and electronic properties. Sulfur-doped hematite was synthesized by microwave irradiation. The samples were investigated by X-ray diffraction and energy dispersive X- ray-scanning electron microscopy. Nanostructure particles have a hexagonal structure that did not change after sulfur incorporation. The optical studies via UV–Visible spectroscopy proved the high absorbance of S/α-Fe₂O₃under the visible region. Moreover, the band gap of S/α-Fe₂O₃ was shifted to higher wavelengths. However, nonmetals may exhibit a negative effect and act as recombination centers as the photoactivity of undoped hematite was still higher in the photodegradation of methyl orange as a pollutant. H₂O₂ as an oxidant was fourfold better than O₂, leading to the formation of the active oxygen species. The preparation method plays a crucial role in the shaping of nanostructure particles and its photoactivity.     

Electrophysical properties of solid solutions of Zn2 − x (Zr a Sn b )1 − x Fe2x O4 compositions

The electrophysical properties of the multicomponent Zn₂ZrO₄ ? Zn₂SnO₄ ? ZnFe₂O₄ system are studied. The electrophysical parameters of solid solutions of Zn_{2 ? x} (Zr _a Sn _b )_{1 ? x} Fe_2x O₄ (x = 0–1.0, Δx = 0.1, a + b = 1) are determined. It is found that the formed solid solutions are semiconductors with electrophysical properties that change in a regular fashion with composition and are distinguished by high values of resistivity (107–1012 Ω cm).     

GPS patch antenna performance by modification of Zn(1−x)CaxAl2O4-based microwave dielectric ceramics

This study reports the characterization, fabrication, and performance of global positioning systems (GPS) patch antennas as a function of calcium (Ca) concentration and dielectric constant (? _r ). Zn_(1?x)Ca_xAl₂O₄ (x = 0.00, 0.05, 0.10, 0.20, 0.25, and 0.30) thin films were prepared through a sol–gel method. The effects of added Ca on the nanostructures and dielectric properties of ZnAl₂O₄ ceramics were investigated. The addition of Ca increased the crystallite size, grain size, and surface morphology, thereby increasing the density and dielectric constant. As the Ca content increased, the ? _r values linearly increased. However, the Q _u values decreased (at x = 0.25 to x = 0.25) after achieving the optimum values at x = 0.20. Finally, GPS patch antennas were successfully fabricated using the Zn_(1?x)Ca_xAl₂O₄ material. The patch antenna sizes decreased as ? _r increased from 2.88  × 4.37 cm (? _r  ≈ 8.52) to 2.88  × 4.37 cm (? _r  ≈ 10.16). The performance (return loss analysis) and operating frequencies of the GPS patch antennas were measured using the PNA series network analyzer. Results show that the patch antenna resonates at frequency of 1.570 GHz and produces a return loss bandwidth between ?16.6 and ?27.5 dB. The optimal performance of GPS patch antenna with ? _r  ≈ 9.95, Q _u  ≈ 6,186, and return loss = ?27.5 dB was obtained from specimen using Zn_0.80Ca_0.20Al₂O₄ (x = 0.20) ceramics.     

Spark plasma sintering synthesis of Ni1−xZnxFe2O4 ferrites: Mössbauer and catalytic study

Nickel-zinc ferrite nanoparticles, Ni_1−xZn_xFe₂O₄ (x = 0, 0.2, 0.5, 0.8, 1.0) were prepared by combination of chemical precipitation and spark plasma sintering (SPS) techniques and conventional thermal treatment of the obtained precursors. The phase composition and structural properties of the obtained materials were investigated by X-ray diffraction and Mössbauer spectroscopy and their catalytic activity in methanol decomposition was tested. A strong effect of reaction medium leading to the transformation of ferrites to a complex mixture of different iron containing phases was detected. A tendency of formation of Fe-carbide was found for the samples synthesized by SPS, while predominantly iron-nickel alloys ware registered in TS obtained samples. The catalytic activity and selectivity in methanol decomposition to CO and methane depended on the current phase composition of the obtained ferrites, which was formed by the influence of the reaction medium.     

Recent advances in N-heterocycles synthesis through catalytic C−H functionalization of azobenzenes

Azobenzenes are well known as crucial structural motifs used in material sciences, nonlinear optical devices, and pharmaceuticals. They also represent an important class of organic intermediates for the transformation of azo and azoxy groups into various useful molecules. Azo groups have a dual character, both electronically increasing the reactivity of the aryl ring and controlling the site-selectivity of the reaction, which significantly increases their utility in organic synthesis. As a complement to previous protocols, the strategy of transition-metal-catalyzed C–H activation of azobenzenes using various coupling partners, such as alkenes, alkynes, aldehydes, diazo esters, organic azides, and sulfoxonium ylides, has recently emerged as a powerful tool to create the corresponding heterocycles. Thus, this review focuses on the recent progress on the direct synthesis of N-heterocycles via C(sp²)–H functionalization of azobenzenes using transition-metal catalysis. This review includes most of the reported methods until the beginning of 2018.     

Perovskite-related oxynitrides – Recent developments in synthesis,characterisation and investigations of physical properties

Since the first investigations of perovskite type oxynitrides with the generalised composition ABO_3?xN_x about twenty years ago, these compounds have become of growing interest. The incorporation of nitride ions in the perovskite lattice results in distinct changes in the electronic structure leading to unusual physical properties. In this article we report on new synthesis techniques, different analytical methods, progress in the structural characterisation by comprehensive diffraction techniques and local spectroscopic methods like XAS and NMR as well as state of the art theoretical investigations. Various physical characteristics like electrical and thermal transport parameters and dielectric properties are described. The thermal and chemical stability of oxynitride perovskites are investigated and their applications in different photocatalytic reactions are discussed.     

Glycine-assisted hydrothermal synthesis of nanostructured Co x Ni1−x –Al layered triple hydroxides as electrode materials for high-performance supercapacitors

Nanostructured Co _x Ni_1−x –Al layered triple hydroxides (Co _x Ni_1−x –Al LTHs) have been successfully synthesized by a facile hydrothermal method using glycine as chelating agent. The samples were characterized by X-ray diffraction, thermogravimetry, Fourier transform infrared spectroscopy and scanning electron microscopy. The morphologies of Co _x Ni_1−x –Al LTHs varied with the Co content and its effect on the electrochemical behavior was studied by cyclic voltammetry and galvanostatic charge–discharge techniques. Electrochemical data demonstrated that the Co _x Ni_1−x –Al LTHs with Co/Ni molar ratio of 3:2 owned the best performance and delivered a maximum specific capacitance of 1,375 F g⁻¹ at a current density of 0.5 A g⁻¹ and a good high-rate capability. The capacitance retained 93.3% of the initial value after 1,000 continuous charge–discharge cycles at a current density of 2 A g⁻¹.     

Adhesive and electrical properties of the interface between Pb1 − x Mn x Te Crystals and In-Ag-Au alloy

The effect of annealing of Pb_{1 ? x} Mn _x Te crystals at ～690 K and structures on their basis at ～383 K on the adhesive and electric properties of the interface in the Pb_{1 ? x} Mn _x Te-(In-Ag-Au) structure was studied over the temperature range ～77–300 K. The contacts possessed high adhesive strength. The effect of annealing on contact resistance r _c was determined by a change in the specific resistance of crystals, diffusion of Ag atoms into the near-contact area of crystals, and the formation of intermediate phases of the Ag₂Te type at the interface.     

Structures and optical properties of Zn1?x Ni x O nanoparticles by coprecipitation method

Nanocrystals of undoped and nickel-doped zinc oxide (Zn_1?x Ni _x O, where x?=?0.00?C0.05) were synthesized by the coprecipitation method. Crystalline size, morphology, and optical absorption of prepared samples were determined by X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM), and UV?Cvisible spectrometer. XRD and SEM studies revealed that Ni-doped ZnO crystallized in hexagonal wurtzite structure. Doping of ZnO with Ni²⁺ was intended to enhance the surface defects of ZnO. The incorporation of Ni²⁺ in place of Zn²⁺ provoked an increase in the size of nanocrystals as compared to undoped ZnO. Crystalline size of nanocrystals varied from 10 to 40?nm as the calcination temperature increased. Enhancement in the optical absorption of Ni-doped ZnO indicated that it can be used as an efficient photocatalyst under visible light irradiation. Optical absorption measurements indicated a red shift in the absorption band edge upon Ni doping. The band gap value of prepared undoped and Ni-doped ZnO nanoparticles decreased as annealing temperature was increased up to 800?°C.     

Electrode performance and X-ray absorption spectroscopy of La0.8Sr0.2Mn1−x Cu x O3 (0 ≤ x ≤ 0.2)–GDC composite cathodes for SOFCs

Electrochemical properties of composite cathodes consisting of La_0.8Sr_0.2Mn_1?x Cu _x O₃ (LSMCu, 0?≤?x?≤?0.2) and Ce_0.8Gd_0.2O_2?x (GDC) were determined by impedance spectroscopy, and conduction mechanism for the composite cathodes was investigated by a near-edge X-ray absorption fine-structure analysis (NEXAFS). LSMCu–GDC cathodes showed lower polarization resistance (R _p) than LSM–GDC up to 750 °C, whereas they exhibited better performance at higher temperature (≥800 °C). The best performance was achieved with the LSMCu10–GDC cathode: 0.27 and 0.08?Ω cm² at 800 °C and 850 °C, respectively. NEXAFS and refinement results confirmed that Cu doping caused the oxidation of Mn³⁺ to Mn⁴⁺ and lattice contraction. This additional Mn⁴⁺ can lead to the formation of oxygen vacancies when Mn⁴⁺ is converted to Mn³⁺ at relatively high temperatures (above 600 °C). This in turn contributes to improved oxygen ion transport in LSM. The LSMCu–GDC composite cathode can thus be considered a suitable potential cathode for SOFC applications.     

Synthesis of sol–gel Na2Zr x Ti6−x O13 (0≤x≤1) materials and their performance in photocatalytic degradation of organic dyes

In this work we present the synthesis and characterization of four compositions of the solid solution with the general formula Na₂Zr _x Ti_6−x O₁₃ (0≤x≤1) which was prepared by a sol-gel method. The main goal of this work is to evaluate the influence of the incorporation of different amounts of zirconium into the binary phase Na₂Ti₆O₁₃ on two properties: the textural surface and E _g values. This titanate phase crystallizes in a monoclinic unit cell and is built into an octahedral TiO₆ framework forming a rectangular tunnel structure. Additionally, we have compared their photocatalytic performances in degradation of organic dyes under visible light. The heat-treated sol-gel samples were characterized by X-ray powder diffraction, N₂ physisorption, thermal analysis, UV and FT-IR spectroscopy. According to the X-ray powder diffraction results, the new ternary tunnel compound Na₂ZrTi₅O₁₃ was obtained as a single phase at 800°C. The cell parameters for the two end-member phases of that solid solution were refined to confirm that Zr ion was incorporated into the structural framework. This ternary compound had an E _g value of about 2.9 eV. The activity of all heat-treated Na₂ZrTi₅O₁₃ samples was tested in the photocatalytic degradation of methylene blue and Rhodamine B under visible light. The Na₂ZrTi₅O₁₃ calcined at 400°C showed the best performance with 95% of photodegradation of methylene blue and a half time t _1/2 of 15 min.