Cathodic electrosynthesis of CuFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/CuO composite nanostructures for high performance supercapacitor applications

In this work, CuFe₂O₄/CuO nanocomposites have been synthesized by galvanostatic cathodic electrodeposition. The obtained nanocomposites were characterized by field emission scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, Fourier Transform Infrared, and Brunauer–Emmett–Teller surface area analysis. The electrochemical properties of CuFe₂O₄/CuO nanocomposites were evaluated by cyclic voltammetry, galvanostatic charge–discharge cycling, and electrochemical impedance spectroscopy in 1.0 M KOH. The CuFe₂O₄/CuO nanocomposites have shown the high specific capacitance of 322.49 F g^?1 at the scan rate of 1 mV s^?1. After 5000 cycles, 92% of this specific capacitance was retained. Although the prepared nanocomposite has shown a mediocre specific capacitance compared to other metal oxide-based materials, the low cost of the starting materials and the ease of preparation make this nanocomposite a good candidate for supercapacitor applications.     

Enhanced electrochemiluminescence behavior of C,N quantum dots embedded g-C<Subscript>3</Subscript>N<Subscript>4</Subscript> nanosheets and its sensing application for copper (II)

Electrochemiluminescence (ECL) is a very sensitive method for trace analysis because of its background interference and high signal-to-noise ratio. In the past decade, the determination of Cu²⁺ in environment has attracted considerable attention since it plays an essential role in many physiological processes. Herein, a novel ECL sensor based on C,N quantum dots embedded g-C₃N₄ nanosheets (C,N-QDs@NSs) was constructed for the detection of Cu²⁺. The nanocomposite was rapidly obtained via the oxidation of normal g-C₃N₄ in H₂O₂ solution using sonochemical synthesizing method. Due to the abundant surface defects on C,N-QDs@NSs, the ECL intensity was magnified 2.5 times for using a C,N-QDs@NSs electrode in comparision to a g-C₃N₄ modified electrode. Besides, C,N-QDs@NSs could accelerate the rate of electron transfer in ECL reaction and thus resulted in the lower cathodic peak potential. Significantly, Cu²⁺ could effectively quench the ECL of C,N-QD@NSs, which endowed C,N-QD@NSs with a great advantage in the ECL detection of Cu²⁺. under optimum conditions, C,N-QDs@NSs modified electrode exhibited a linear detection range from 5 × 10^?4 to 10 µM with a detection limit of 2 × 10^?4 µM (S/N?=?3) for Cu²⁺, and was finally applied to detect Cu²⁺ in real samples with satisfactory results.     

Cu doping effect on the resistive switching behaviors of CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> thin films

Spin-coated Cu_xCo_1?xFe₂O₄ (x = 0, 0.2, 0.4, 0.6, and 0.8) thin films were prepared on Pt/TiO₂/SiO₂/Si substrates. Pt/Cu_xCo_1?xFe₂O₄/Pt structures were fabricated to investigate the effect of Cu doping concentration on the resistive switching behaviors. Structural and morphology characterizations revealed that Cu doping improved the crystallization of the thin films as compared to undoped CoFe₂O₄. Current–voltage characterization showed that all Cu_xCo_1?xFe₂O₄ thin films showed unipolar resistance switching, but the distribution range of the set voltage, reset voltage, and resistances were much reduced by Cu doping. Clear improvement in the stability of these parameters started to appear with x = 0.4, and the optimized performance was observed in the Pt/Cu_0.6Co_0.4Fe₂O₄/Pt structure. The improved stability of the switching parameters was attributed to the enhancement of hopping process between the Fe ions and the Cu ions in the spinel lattice. Our results indicated that appropriate adjustment of the doping elements in oxides can be a feasible approach in achieving stable resistance switching memory devices.     

Effect of potassium on the structure and catalytic properties of K<Subscript>1.2</Subscript>Cu<Subscript>0.4</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript>

We have studied the structural properties of the phase K_1.2Cu_0.4Fe₂O₄ and the effect of potassium on its catalytic activity for oxidation of carbon. The results demonstrate that the potassium-doped phase differs from the undoped ferrite CuFe₂O₄ in linear dimensions of its unit cell, high density of structural defects, and low-temperature activity and activation energy for the catalytic process. Contact interaction between K_1.2Cu_0.4Fe₂O₄ and carbon in the temperature range 240–420°C leads to the reduction of Cu²⁺ to Cu⁺ and the formation of Cu₂O, CuFeO₂, and K₂Fe₄O₇. Testing results for the phases identified indicate that the catalytic processes in the presence of K₂Fe₄O₇ and K_1.2Cu_0.4Fe₂O₄ are identical.     

Microwave Synthesis of Cu/Cu<Subscript>2</Subscript>O/SnO<Subscript>2</Subscript> Composite with Improved Photocatalytic Ability Using SnCl<Subscript>4</Subscript> as a Protector

Cu/Cu₂O/SnO₂ composites were successfully prepared with a facile microwave synthesis method. The structure of Cu/Cu₂O/SnO₂ composite was studied by morphology characterizations, such as X-ray diffraction, transmission electron microscopy and high-resolution transmission electron microscopy, which showed that the size of the Cu/Cu₂O/SnO₂ particles is 20–50 nm. The synthesis mechanism revealed that SnCl₄ obstructed between Cu(OH) and ethylene glycol, preventing Cu(OH) being reduced into Cu at high temperature. The photocatalytic property of Cu/Cu₂O/SnO₂ composite was investigated by degrading the mixed dyestuff under the irradiation of visible light at room temperature. Benefiting from the effect of electron transfer, the photocatalytic performance of the microwave-prepared Cu/Cu₂O/SnO₂ composite was much better than that of pure Cu₂O. The possible photocatalytic mechanism of the Cu/Cu₂O/SnO₂ composite catalysts was proposed and elaborated in this study. This synthesis of Cu/Cu₂O/SnO₂ composite may provide a method for other Cu₂O/semiconductor composites microwave preparation.     

Reduced graphene oxide/Cu<Subscript>2</Subscript>O nanostructure composite films as an effective and stable hydrogen evolution photocathode for water splitting

An efficient photocathode consisting of reduced graphene oxide/Cu₂O/Cu (rGO/Cu₂O/Cu) has been successfully prepared in this work via a facile two step method, consisting of chemical oxidation of a copper foil in alkaline solution using (NH₄)₂S₂O₈ as the oxidizing agent, dipping the prepared samples in graphene oxide (GO) solution and calcination at vacuum to form a rGO layer onto Cu₂O/Cu photocathode, which acts as a protective layer. The products were composed of a thin Cu₂O layer topped with a thin rGO film as the protective coating. The chemical composition and rGO amount in the composite materials were easily controlled by changing the immersion time to enhance PEC performance. UV–Vis spectroscopy, Raman spectroscopy, XRD, SEM, TEM and FTIR spectroscopy were used in the optical and morphological characterization of the graphene oxide and prepared photocathodes. Distinct patches of GO film are formed on the Cu(OH)₂ nanostructure surface, as shown by SEM results. Linear sweep voltammetry and chronoamperometry analysis have been applied in the photoelectrochemical characterizations in the dark and under illumination conditions. Photocurrent density provided by rGO/Cu₂O/Cu photocathode ??2.54 mA cm^??2 is three times greater than that of bare Cu₂O/Cu photocathode ??0.82 mA cm^??2 at 0 V vs. RHE under illumination. Low photostability of 42% is exhibited by bare Cu₂O/Cu photocathode after 200 s irradiation whereas rGO/Cu₂O/Cu photocathode shows approximately 98% of the initial photocurrent density. Therefore, a strategy has been developed in this work for the synthesis of this new photocathode using Cu₂O/Cu as an effective photocathode for photoelectrochemical (PEC) water splitting.     

High-performance flexible supercapacitors based on C/Na<Subscript>2</Subscript>Ti<Subscript>5</Subscript>O<Subscript>11</Subscript> nanocomposite electrode materials

A new solution method to synthesize Na₂Ti₅O₁₁ with titanium powder is presented, and the C/Na₂Ti₅O₁₁ nanocomposite with high specific surface area and tunnel structure as the electrode material has excellent electrochemical performance. The single electrode composed of the C/Na₂Ti₅O₁₁ nanocomposite based on carbon fiber fabric (CFF) has the highest area capacitance of 1066 mF cm^?2 at a current density of 2 mA cm^?2, which is superior to other titanates and Na-ion materials for supercapacitors (SCs). By scan-rate dependence cyclic voltammetry analysis, the capacity value shows both capacitive and faradaic intercalation processes, and the intercalation process contributed 81.7% of the total charge storage at the scan rate of 5 mV s^?1. The flexible symmetric solid-state SCs (C/Na₂Ti₅O₁₁/CFF//C/Na₂Ti₅O₁₁/CFF) based on different C/Na₂Ti₅O₁₁ mass were fabricated, and 7 mg SCs show the best supercapacitive characteristics with an area capacitance of 309 mF cm^?2 and a specific capacitance of 441 F g^?1, it has a maximum energy density of 22 Wh kg^?1 and power density of 1286 W kg^?1. As for practical application, three SCs in series can power 100 green light-emitting diodes (LEDs) to light up for 18 min, which is much longer than our previous work by Wang et al. lighting 100 LEDs for 8 min. Thus, the C/Na₂Ti₅O₁₁ nanocomposite has promising potential application in energy storage devices.     

Light weight RGO/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanocomposite for efficient electromagnetic absorption coating in X-band

Reduced graphene oxide (RGO)/magnetite (Fe₃O₄) nanocomposite has been synthesized by an in-situ facile hydrothermal method. The XRD pattern reveals the development of nanocomposite in which both phases are coexistent. Raman Spectroscopy shows the main characteristics peaks of D and G bands at 1349 cm^?1 and 1595 cm^?1 for graphitic structures. The intensity ratio (I_D/I_G) is also calculated, which indicate the degree of defects in the material. This ratio (I_D/I_G), increases from 0.84 for GO to 0.91 for RGO/Fe₃O₄ nanocomposite and promotes the defects which are beneficial for electromagnetic (EM) absorption. The SEM image depicts that, Fe₃O₄ spherical nanoparticles are dispersed over the surface of graphene sheets and provide a thermal conducting path for heat dissipation between different layers of graphene. The EM absorption properties have been analyzed at 2–18 GHz of RGO and RGO/Fe₃O₄. The addition of proper content of Fe₃O₄ magnetic nanoparticles in RGO sheets improved the Reflection Loss (RL) from ??13.5 dB to ??20 dB at a frequency of 9.5 GHz. Moreover, due to magnetic loss and interfacial polarization, the effective bandwidth increases from 2.5 GHz to 3.8 GHz at a coating thickness of 1.5 mm. Hence this light weight nanocomposite is an excellent material for strong EM absorption in X-band.     

Synthesis and microwave absorption property of ternary composites: polyaniline/CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/Ba<Subscript>3</Subscript>Co<Subscript>2</Subscript>Fe<Subscript>24</Subscript>O<Subscript>41</Subscript>

Polyaniline (PANI)/CoFe₂O₄/Ba₃Co₂Fe₂₄O₄₁ composite was prepared by an in-situ polymerization method. The phase structure, morphology and magnetic properties of the as-prepared PANI/CoFe₂O₄/Ba₃Co₂Fe₂₄O₄₁ composite were characterized by XRD, FT-IR, SEM, TEM, and VSM, respectively. The microwave absorption properties of the composite were investigated by using a vector network analyzer in the 2–18 GHz frequency range. The results show that the maximum reflection loss value of the PANI/CoFe₂O₄/Ba₃Co₂Fe₂₄O₄₁ composite reaches ?30.5 dB at 10.5 GHz with a thickness of 3 mm and the bandwidth of reflection loss below ?10 dB reaches up to 1.2 GHz. The excellent microwave absorption properties of the as-prepared PANI/CoFe₂O₄/Ba₃Co₂Fe₂₄O₄₁ composite due to the enhanced impedance match between dielectric loss and magnetic loss.     

Growth and properties of Cu<Subscript>2</Subscript>ZnSnS<Subscript>4</Subscript> thin films prepared by multiple metallic layer stacks as a function of sulfurization time

In this paper, we report the two stage growth of Cu₂ZnSnS₄ (CZTS) thin films as a function of sulfurization time. First, magnetron sputtered metallic precursors were deposited sequentially (Zn/Cu/Sn/Cu) over rotating glass substrates held at 230?°C. Later, the sputtered precursors were heat treated at 500?°C in the ambiance of sulfur for various time durations in the range, 10–120 min. The sulfur treated samples were examined using various analytical tools to understand the role of sulfurization time on the CZTS growth and properties. From composition and structural analysis, Zn/Cu/Sn/Cu precursors sulfurized for shorter duration (10 and 20 min) revealed severe deficiency of sulfur that resulted in several metallic, bi-metallic and metal sulfide phases. With the increase of sulfurization time to 30 min, sulfur incorporation was enhanced and reached stoichiometric ratio (~50% S) for CZTS growth, however, samples were poorly crystalline in nature and consisted of prominent Cu_2?xS phase as well. The Zn/Cu/Sn/Cu precursors sulfurized for 60 min exhibited prominent CZTS phase without Cu_2?xS phase. Further, rise in sulfurization time to 120 min enabled drastic improvement in crystallinity of CZTS phase. Raman mapping over 60 µm × 60 µm for these films confirmed the homogeneous phase growth of CZTS. XPS study revealed the oxidation states of Cu¹⁺, Zn²⁺, Sn⁴⁺ and S^2? in CZTS films. The optimized films showed high absorption coefficient of 10⁵ cm^?1 with an optical band gap of 1.51 eV. These films showed leaf like grain morphology with high mobility and low resistivity of 18.2 cm²/V-s and 0.7 Ω-cm, respectively.     

Influence of different dopant sites by lanthanum on the dielectric properties of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> ceramics

The effects of La³⁺ doped in calcium copper titanate (CCTO) at Ca²⁺ site and Cu²⁺ site were examined. The doped compositions, La_0.1Ca_0.85Cu₃Ti₄O₁₂ (LCCTO) ceramics and CaLa_0.1Cu_2.85Ti₄O₁₂ (CLCTO) ceramics were prepared by the solid-state method. The microstructure, dielectric properties, complex impedance and nonlinear I–V characteristics were studied. And it was found that La³⁺ doped at Ca²⁺ site achieved lower sintering temperatures than that doped at Cu²⁺ site in CCTO ceramics. The dielectric loss (tan δ) of LCCTO ceramics was about 0.05 at 40 kHz when the sample was sintered at 1080 °C. Dielectric constant (ε′) of LCCTO ceramics was about 3.2 × 10⁴ when the sample was sintered at 1100 °C, which was larger than CLCTO ceramics examined under the same process condition with sintering temperatures vary. The impedance analysis revealed that LCCTO ceramics had an influence of resistance of grain boundaries, which was stronger than that of CLCTO ceramics. Meanwhile, both LCCTO ceramics and CLCTO ceramics had a nonlinear-Ohmic property.     

Enhanced electrochemical reduction of hydrogen peroxide by Co<Subscript>3</Subscript>O<Subscript>4</Subscript> nanowire electrode

Crystalline Co₃O₄ nanowire arrays with different morphologies grown on Ni foam were investigated by varying the reaction temperature, the concentration of precursors, and reaction time. The Co₃O₄ nanowires synthesized under typical reaction condition had a diameter range of approximately 500–900 nm with a length of 17 µm. Electrochemical reduction of hydrogen peroxide (H₂O₂) of the optimized Co₃O₄ nanowire electrode was studied by cyclic voltammetry. A high current density of 101.8 mA cm^?2 was obtained at ?0.4 V in a solution of 0.4 M H₂O₂ and 3.0 M NaOH at room temperature compared to 85.8 mA cm^?2 at ?0.35 V of the Co₃O₄ nanoparticle electrode. Results clearly indicated that the Ni foam supported Co₃O₄ nanowire electrode exhibited superior catalytic activity and mass transport kinetics for H₂O₂ electrochemical reduction.     

Facile synthesis of Mg(OH)<Subscript>2</Subscript>/graphene oxide composite by high-gravity technology for removal of dyes

A facile high-gravity strategy is proposed for preparation of Mg(OH)₂/graphene oxide (MGO) composite using a rotating packed bed reactor at room temperature for 1 min. Lamellar Mg(OH)₂ nanocrystals of about 60 nm in diameter with a narrow size distribution are distributed homogeneously on the graphene oxide sheets without aggregation. The specific surface area of MGO with mesoporous structure reaches 590 m² g^?1, which is the highest among those reported in the literatures. The as-prepared MGO nanocomposite exhibits excellent adsorption capacity for methylene blue (MB). The removal rate of MB reaches 98% in 1 min. The preparation process of MGO nanocomposite is rapid, simple, and suitable for a large-scale production, and the product has great potential in the field of environmental protection as a promising absorbent.     

Dielectric responses of Na<Subscript>0.65</Subscript>Bi<Subscript>0.45</Subscript>Cu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> ceramics based on the composition design of changing the Na/Bi ratio

Na_0.65Bi_0.45Cu₃Ti₄O₁₂ ceramics were successful prepared by the conventional solid-state reaction technique. Compared to Na_0.50Bi_0.50Cu₃Ti₄O₁₂ (NBCTO), the composition of Na_0.65Bi_0.45Cu₃Ti₄O₁₂ was designed in terms of changing the Na/Bi ratio. Colossal dielectric permittivity of ~1.2 × 10⁴ at 1 kHz was obtained in Na_0.65Bi_0.45Cu₃Ti₄O₁₂ ceramics. Interestingly, three frequency dispersions were observed in the frequency dependence of dielectric constant measured at different temperatures. The investigation of electric modulus displayed that the giant low-frequency dielectric constant was attributed to Maxwell–Wagner polarization at the grain boundaries and the frequency dispersion in middle-frequency range was due to the grain polarization. Except grain response and grain boundaries response reflected by two semicircles in the impedance spectroscopy, another electrical response associated with nonzero high frequency intercept was found. The grain resistance Rg and grain boundaries resistance R _gb was ~600 Ω and 3.9 × 10⁵ Ω, respectively. The large intrinsic permittivity as high as ~700 was obtained. Furthermore, two dielectric anomalies observed in the temperature dependent of dielectric constant were discussed in detail. The results indicated change in the Na/Bi ratio had a significant effect on the electrical properties of NBCTO ceramics.     

Rietveld analysis of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> thin films obtained by RF-sputtering

Calcium copper titanate, CaCu₃Ti₄O₁₂, CCTO, thin films with polycrystalline nature have been deposited by RF sputtering on Pt/Ti/SiO₂/Si (100) substrates at a room temperature followed by annealing at 600 °C for 2 h in a conventional furnace. The crystalline structure and the surface morphology of the films were markedly affected by the growth conditions. Rietveld analysis reveal a CCTO film with 100 % pure perovskite belonging to a space group Im3 and pseudo-cubic structure. The XPS spectroscopy reveal that the in a reducing N₂ atmosphere a lower Cu/Ca and Ti/Ca ratio were detected, while the O₂ treatment led to an excess of Cu, due to Cu segregation of the surface forming copper oxide crystals. The film present frequency -independent dielectric properties in the temperature range evaluated, which is similar to those properties obtained in single-crystal or epitaxial thin films. The room temperature dielectric constant of the 600-nm-thick CCTO films annealed at 600 °C at 1 kHz was found to be 70. The leakage current of the MFS capacitor structure was governed by the Schottky barrier conduction mechanism and the leakage current density was lower than 10^?7 A/cm² at a 1.0 V. The current–voltage measurements on MFS capacitors established good switching characteristics.     

Synthesis and crystal structure of Cu<Subscript>2</Subscript>{(UO<Subscript>2</Subscript>)<Subscript>3</Subscript>[(S,Cr)O<Subscript>4</Subscript>]<Subscript>5</Subscript>}(H<Subscript>2</Subscript>O)<Subscript>17</Subscript>

Cu₂{(UO₂)₃[(S,Cr)O₄]₅}(H₂O)₁₇ crystals were prepared by evaporation of aqueous solutions. The crystal structure was solved by the direct method and refined to R ₁ = 0.064 (wR ₂ = 0.177) for 8120 reflections with ¦F _hkl¦ 4 ¦F _hkl¦. Rhombic system, space group Pbca, a = 18.0586(8), b = 19.9898(9), c = 20.5553(8) Å, V = 7420.2(6) ų. The structure is based on {(UO₂)₃[(S,Cr)O₄]₅}^4– anionic layers, formed by combination of UO₇ pentagonal bipyramids and TO₄ tetrahedra through common vertices. The { (UO₂)₃ [(S,Cr)O₄]₅}^4– layers are parallel to the (010) plane. The Cu²⁺ (H₂O)₆ octahedra and additional water molecules are located in the interplanar space and provide binding of the layers in the structure by hydrogen bonds. Based on the occupancy of tetrahedral positions, more accurate chemical formula of the compound should be written as Cu₂{(UO₂)₃[(S_0.804 Cr_0.196)O₄]₅} (H₂O)₁₇.Translated from Radiokhimiya, Vol. 46, No. 5, 2004, pp. 408–411.Original Russian Text Copyright © 2004 by Krivovichev, Burns.     

Facile synthesis and excellent electromagnetic wave absorption properties of flower-like porous RGO/PANI/Cu<Subscript>2</Subscript>O nanocomposites

Novel porous ternary nanocomposite systems containing reduced graphene oxide (RGO)/polyaniline (PANI)/cuprous oxide (Cu₂O) were prepared via one-step in situ redox method. The RGO/PANI/Cu₂O nanocomposites present a flower-like structure with an average size of 2.0 μm in diameter. The morphologies and properties of the products can be controlled by adjusting the molar ratios of aniline to Cu²⁺. When the molar ratio of aniline to Cu²⁺ is 1:1, the product exhibits excellent microwave absorption property in the frequency range of 2–18 GHz. It can be seen that the maximum reflection loss (RL) of the ternary composite is up to ?52.8 dB at 2.7 GHz with a thickness of only 2 mm, and the absorption bandwidth corresponding to ?10 dB (90% of EM wave absorption) is 13.2 GHz. The microwave absorption property of ternary RGO/PANI/Cu₂O composite is significantly improved due to its special flower-like porous structure, dielectric loss property and well impedance matching characteristics, which is 8.12 times than that of pure RGO and 5.28 times than that of pure PANI. Therefore, our study paves a new way to prepare the promising lightweight and high-performance composite materials combined with the characteristics of three components for electromagnetic absorption.     

Investigation of Li<Subscript>2</Subscript>Zn<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript>-based temperature stable dielectric ceramics for LTCC applications

A low temperature co-fired ceramic (LTCC) was fabricated at 910 °C /2 h from the powder mixture of Li₂Zn₃Ti₄O₁₂, TiO₂ and a B₂O₃–La₂O₃–MgO–TiO₂ glass (BLMT), and the influence of TiO₂ on microstructure and dielectric properties of the composite was investigated in the composition range (wt%) of 20BLMT–(80???x)Li₂Zn₃Ti₄O₁₂–xTiO₂ (x?=?0, 2.5, 5, 7.5, 9 and 10). The results showed that all samples consisted of Li₂Zn₃Ti₄O₁₂, TiO₂, LaBO₃ and LaMgB₅O₁₀ phase. And LaBO₃, LaMgB₅O₁₀ and a small amounts of TiO₂ were crystallized from BLMT glass during sintering process. As x increases, dielectric constant and temperature coefficient of resonance frequency of the composites demonstrated gradually increase, whereas the quality factor of the sample of x?=?0 wt% was about 41,500 GHz and the ones maintained stable at a high level of 49,000–51,000 GHz for other samples. The composite with x?=?9 wt% had an optimal microwave dielectric properties with the dielectric constant of 20.2, quality factor of 50,000 GHz and temperature coefficient of resonant frequency of ??0.33 ppm/°C.     

Controlled magnetoresistance in Y<Subscript>3/4</Subscript>Lu<Subscript>1/4</Subscript>Ba<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7</Subscript>-CuO composites at 77 K

We have studied the low-temperature magnetoresistance of Y_3/4Lu_1/4Ba₂Cu₃O₇-CuO composites obtained by fast sintering technique and established a relation between the probing to critical current density ratio j/j _c and the shape of the magnetoresistance curve ρ(H). For j/j _c<1, the electric resistance arises at a threshold value of the magnetic field strength H _c. For j/j _c≥1, a linear variation of ρ(H) at 77 K in the range from 0 to 14 Oe can be provided by selecting the CuO content (in the 15–30 vol % interval) and the j value (in the 0.003–0.2 A/cm² range). In the latter case, the slope dρ/dH (i.e., the sensitivity of the electric resistivity with respect to the magnetic field) is 1–20 mΩ cm/Oe and the relative field-induced increase in the resistivity ρ₀=(ρ(H)−ρ(H=0))/ρ(H=0) amounts to 1320 and 685% at H=200 and 35 Oe, respectively. Composites possessing controlled magnetoresistance are promising materials for the active elements of magnetic field sensors capable of operating at a practically convenient liquid nitrogen temperature.     

Preparation and electrochemical behavior of methylene blue intercalated into layered niobate K<Subscript>4</Subscript>Nb<Subscript>6</Subscript>O<Subscript>17</Subscript>

K₄Nb₆O₁₇ nano-layered compound was obtained by solid-phase synthesis and then methylene blue (MB) was intercalated into layered niobate K₄Nb₆O₁₇ interlayer I by a two-step guest-guest exchange method using the intercalation compound, methyl viologen (MV²⁺)–K₄Nb₆O₁₇, as precursor. The optically transparent MB⁺–K₄Nb₆O₁₇ nanocomposite thin film has been characterized by XRD, IR, TGA, elemental analysis, UV, and electrochemical measurements. It was estimated that the intercalated MB⁺ ions are mainly aggregated. The cyclic voltammogram of the MB⁺–K₄Nb₆O₁₇ nanocomposite thin film exhibited a fine diffusion-controlled cathodic process, which hints the possibility of being utilized as an electrode modifying material.