Preparation and electrochemical characterization of Ti/Ru x Mn1−x O2 electrodes

DSA^® type electrodes of ruthenium–manganese mixed oxides (30 at % Ru < 100) supported on titanium were prepared by the spray-pyrolysis technique, using Ru(NO)(OH) _x (NO₃)_3–x and Mn(NO₃)₂ as precursors. Electrodes were characterized by SEM, XRD and cyclic voltammetry. Their behaviour as anode for the chlorine and oxygen evolution reactions was also evaluated by polarization curves. The stability of the mixed oxides was determined through accelerated tests of service life. It has been verified that the best performance on the apparent electrocatalytic activity of both reactions as well as on stability is achieved at a composition of about 70% Ru.     

Composition dependence of specific heat in Se80 − x Te20Sn x chalcogenide glasses

Differential Scanning Calorimetry (DSC) is performed at different heating rates under non-isothermal conditions to study the specific heat studies of glassy Se_{80 ? x} Te₂₀Sn _x (0 ≤ x ≤ 10) alloys. An extremely large increase in the specific heat values has been observed at the glass transition temperature. It has also been found that the values of C _p below glass transition temperature (C _pg ) and after glass transition (C _pe ) are highly composition dependent. This indicates that the Sn additive used in the present study influences the structure of the glassy Se₈₀Te₂₀ alloy. The results show that C _p values reveal local extrema in Se-Te-Sn glassy system at x = 4 and x = 8. The composition dependence of both parameters (C _pe and C _pg ) has been explained in terms of the glassy structure of Se-Te-Sn system.     

Strategy for improving the capacity and rate performance of LiNixCoyMn1−x−y electrode using Ti3C2Tx MXene additives

With the expanding range of applications for lithium-ion batteries, a great deal of research is being conducted to improve their capacity, stability, and charge/discharge rates. This study was performed to investigate the effects of MXene, which has a large surface area and metallic conductivity, as a conductive additive to the cathode, on electrochemical performance. The two-dimensional material MXene constructs a conductive network with zero-dimensional carbon black in plane-to-point mode to improve conductivity and contact area with active materials, thereby facilitating fast charge transfer. The conductive network reduces the internal resistance and polarization of the cathode and aids the diffusion of electrons. The electrode containing an appropriate amount of MXene showed improved rate performance, high discharge capacity (123.9 mAh g⁻¹ at 4 C), and excellent cycle stability at a high scan rate (125.8 mAh g⁻¹ at 2 C after 150 cycles) compared to pristine electrodes. Based on these results, Ti₃C₂T_x MXene is a promising conductive additive in the battery field.     

State of manganese atoms in the Nd1+x Sr2−x Mn2O7−δ solid solution

The oxidation state of manganese in the Nd_2?x Sr_1+x Mn₂O_7?δ solid solution was determined by X-ray photoelectron spectroscopy and by calculating the oxygen nonstoichiometry based on the gravimetric data. As a result of the heterovalent replacement of Nd³⁺ with Sr²⁺, the change in the oxidation state of manganese occurs in different ways, i.e., it increases at x > 0 and decreases at x < 0. In the latter case, some oxygen ions acquire the oxidation state of ?1. The samples slowly cooled under oxidative conditions possess a significant positive oxygen non-stoichiometry, which tends to decrease after Nd³⁺ is replaced with Sr²⁺. An excess of oxygen stabilizes the crystal structure of Nd_1+x Sr_2?x Mn₂O_7?δ.     

Catalytic CO2 reforming of methane over Ir/Ce0.9Gd0.1O2−x

CO₂ reforming of methane over Ir loaded Ce_0.9Gd_0.1O_2−x (Ir/CGO) has been studied between 600 and 800 °C and for CH₄/CO₂ ratios between 2 and 0.66 in order to evaluate its potential use as an anode material for direct conversion of biogas at moderate temperatures in solid oxide fuel cells. The catalyst exhibited a superior catalytic activity compared to the support alone and other Ir based catalysts. High CH₄/CO₂ ratios and temperatures were required to obtain the maximum H₂/CO ratio, which could never exceed unity. Long-term experiments were carried out, showing the excellent stability of the catalyst with time on stream. Carbon formation was totally inhibited (in most experimental conditions) or very limited in the most severe conditions of the study (800 °C, CH₄/CO₂ = 2). This carbon was found to be highly reactive towards O₂ upon TPO experiments.     

Thermal decomposition of K1 − x Cs x BSi2O6 borosilicates

Thermal decomposition of mixed K_{1 ? x} Cs _x BSi₂O₆ borosilicates by the methods of thermal analysis, annealing, and quenching, with the following refining of the structure by the Rietveld method on the example of solid solutions with x = 0.3 and 0.7 crystallizing in the space groups $I4\bar 3d$ and $Ia\bar 3d$ , respectively, is studied. It is shown that the solid-phase decomposition of borosilicates proceeds with the release of the gas- eous phase and formation of cristobalite and/or tridymite of SiO₂ at the final stage. In this case the solid solutions enriched by potassium decompose in one stage with the formation of SiO₂, while the solutions enriched by cesium decompose with the formation of the intermediate zeolite-like CsBSi₅O₁₂ borosilicate, which also decomposes during further thermal treatment. According to the data of the structure, the refining of K_{1 ? x} Cs _x BSi₂O₆ solid solutions obtained by thermal treatment at 1000°C for 20, 65, 80, and 100 h, it is detected that for the samples with x = 0.3 and 0.7 the parameter of the cubic cell of the leucite-like phase decreases and the vacancies in the position of alkaline cation appear. During the solid-phase decomposition of K_{1 ? x} Cs _x BSi₂O₆ solid solutions the structure degrades.     

Effect of Thermal Aging on the Transient Kinetics of Oxygen Storage and Release of Commercial Ce x Zr1−x O2-based Solids

The use of powerful analytical methodologies for the evaluation of the performance of commercial oxygen storage materials based on oxygen transient isothermal isotopic exchange experiments is illustrated in this study. Ce _x Zr_1?x O₂-based oxygen storage materials were investigated. The materials were characterized for their dynamic oxygen storage and release properties through the pulse injection technique allowing the measurement of the oxygen storage capacity (OSC), and for their surface and bulk oxygen mobility through transient isothermal ¹⁸O isotopic exchange experiments. Very high OSC values were obtained after calcination in air at T_calc. = 700 or 850 °C. However, after thermal aging at 1000 or 1100 °C of the as prepared samples, a significant deterioration of their OSC was observed. This fact was found to correlate with the significant increase in the activation energy of surface oxygen mobility. On the contrary, smaller increase in the activation energy of bulk oxygen diffusion with increasing T_calc. was observed.     

Microwave dielectric properties of (1−x)ZnTa2O6−xMgNb2O6 ceramics

Single phase MgNb₂O₆ and ZnTa₂O₆ powders were synthesized by solid-state method, and the high quality factor composite ceramics of (1?x)ZnTa₂O₆?xMgNb₂O₆ (x=0, 0.05, 0.10, 0.15, 0.20, 0.25 and 1.0) were prepared using the as-synthesized powders. The microwave dielectric properties, microstructure, phase transition and sintering behavior of the composite ceramics were investigated. The X-ray diffraction analysis revealed that solid solution between ZnTa₂O₆ and MgNb₂O₆ phases appeared in the composite ceramic. SEM results show that the grain sizes of the composite ceramics increased with increasing x values. The temperature coefficient of resonant frequency of (1?x)ZnTa₂O₆?xMgNb₂O₆ composite ceramics reaches near-zero of 1.02 ppm/°C with ε_r=35.58 and a high quality factor of 65500 GHz when x=0.20 and sintered at 1350 °C for 2 h.     

Study on the crystal structure of (Gd2−xCex)Ti2O7 (0 ≤ x ≤ 0.8) pyrochlore

Synthesis, characterisation and crystal structure analysis studies of oxides in (Gd_2?x Ce_x)Ti₂O₇ series have been reported, Ce³⁺ used as a surrogate for Pu³⁺ because they have similar physical and chemical properties. In the present report, a series of pyrochlore-type crystal with composition (Gd_2?x Ce_x)Ti₂O₇ (0?≤?x?≤?0.8) were successfully synthesised by the solution combustion followed by high temperature calcining. The phase purity and crystal structure of samples were investigated by X-ray diffraction analysis as well as Rietveld refinement. It was observed that the solubility of Ce³⁺ in the lattice of Gd₂Ti₂O₇ pyrochlore is 39.62?mol.-%. The calculated lattice parameters and the simulated XRD patterns of (Gd_2?x Ce_x)Ti₂O₇ (x?=?0, 0.5, 1) were obtained based on the density functional theory. The results of theoretical calculation are quite consistent with the results of the experiment. Additionally, the grain size and the visual information about the microscopic structure of the (Gd_2?x Ce_x)Ti₂O₇ crystals were obtained by transmission electron microscopy.     

Influence of Zr/Ti atomic ratio and seed layer on the magnetoelectric coupling of Pb(ZrxTi1−x)O3 film-on-CoFe2O4 bulk ceramic composites

Lead zirconate titanate Pb(Zr_xTi_1−x)O₃ films with various Zr/Ti ratios of 20/80, 40/60, 52/48, 60/40 and 80/20 are deposited on highly dense CoFe₂O₄ ceramics using a simple chemical solution deposition. All Pb(Zr_xTi_1−x)O₃ films are polycrystalline and have no preferential orientations. The dielectric, ferroelectric, piezoelectric and magnetoelectric properties strongly depend on the Zr/Ti ratio. And the Pb(Zr_xTi_1−x)O₃ films with a Zr/Ti ratio close to morphotropic phase boundary exhibit best properties, whose magnetoelectric coefficient is over 1.5 times larger than those of other Zr/Ti ratios. The introduction of a PbO seeding layer between the Pb(Zr_0.52Ti_0.48)O₃ films and CoFe₂O₄ substrates facilitates the (100)-texture. Therefore, the magnetoelectric coefficient was enhanced by 1.5 times. The further improvement of the magnetoelectric coupling could be anticipated by fabricating Pb(Zr_0.52Ti_0.48)O₃ films with more or absolute (100)-texture and using conductive interfacial layer between two phases.     

Effect of pulse reversal on the properties of pulse plated CdSe x Te1−x thin films

CdSe _x Te_1–x thin films with 0 < x < 1 were deposited on titanium and conducting glass substrates by pulse electrodeposition using microprocessor control. Formation of the solid solution takes place for values of x(0 < x < 1). The films were characterized by X-ray diffraction. While the as-deposited films are cubic in nature, those annealed at 475 °C in air indicate hexagonal structure and the lattice parameters increase with increasing value of x. From the optical absorption measurements the band gap of the material was calculated. The value of the band gap varies from 1.42 to 1.70 eV as x varies from 0 to 1. The photoelectrochemical (PEC) characteristics were obtained for all compositions of CdSe _x Te_1–x (x = 0–1). The output parameters for CdSe_0.66Te_0.34 with 9% duty cycle at an intensity of 80 mW cm^–2 using 1 M polysulphide as the redox electrolyte, are V _OC of 398 mV, J _SC of 5.59 mA cm^–2, ff of 0.45, of 4.73%, R _s of 13 , R _sh of 1.50 k. The output parameters were found to increase with 60 ms pulse reversal. After photoetching for 40 s, a V _OC of 481 mV, J _SC of 16.00 mA cm^–2, ff of 0.57, of 5.46%, R _s of 6 , R _sh of 2.16 k were obtained.     

Perovskite forming ceramics of the system SrxLa1−x TiIVx+yCoIIyCoIII1−x−2yO3 for NTC thermistor applications

The paper reports the preparation, structure and electrical properties of oxide ceramic semiconductors based on the series Sr_xLa_1−x Ti^IV_x+yCo^II_yCo^III_1−x−2yO₃ with perovskite type stucture: 0<x<1, 0<y<(1−x)/2. The study starts from LaCoO₃ which is highly conductive yielding metallic condutivity above 330°C. The upset trigonal distortion of LaCoO₃ is reduced when Sr^II/Ti^IV is substituted for La^III/Co^III corresponding to increasing values of x and also when 2 Co^III are introduced for Ti^IV/Co^II into the lattice corresponding to increasing values of y. At high values of x and y othorhombic distortion occurs. At the same time, the interaction between the Co^III atoms of LaCoO₃ is increasingly interrupted providing increasing values of the the resistivity value ρ_25°C and of the B_25/100°C value deduced from measurements at 25 and 100°C according to ρ(T )=ρ_25°C e^B/T. The range of variation of x an y makes possible to prepare ceramics with desired electrical properties within the limits of ρ_25°C=1.1 Ωcm, B=1910 K and ρ_25°C=1 bis 8×10⁶ Ωcm at B-values up to 6500 K. Dependent on composition, NTC ceramics for thermistor or insurance applications are accessible. Thermistors do not show aging even at higher temperature, e.g. at 500°C, provided the single phase state is achieved as a result of mixed oxide preparation and sintering. Hence, high temperature thermistor applications are also made possible. The semiconductor behavior can be understood using the conventional polaron state hopping model.     

New solid solutions of mixed alkali-zinc diphosphates LiNa1 − x K x ZnP2O7

Phase relationships in the LiNaZnP₂O₇-LiKZnP₂O₇ system have been studied. For the first time a vast region of solid solutions of the rhombic syngony LiNa_{1 ? x} K _x ZnP₂O₇ containing simultaneously three alkali cations was found. The miscibility is broken at the temperature of the polymorphous transformations LiKZnP₂O₇ (270°C) and below, with the formation of the two-phase region of the solid solution with the rhombic and monoclinic structures (0.85 ≤ x ≤ 1 at 25°C).     

Catalytic Oxidation of CO Gas over Nanocrystallite Cu x Mn1−x Fe2O4

The catalytic oxidation of CO over nanocrystallite Cu _x Mn_(1−x)Fe₂O₄ powders was studied using advanced quadruple mass gas analyzer system. The oxidation of CO to CO₂ was investigated as a function of reactants ratio and firing temperature of ferrite powders. The maximum CO conversion was observed for ferrite powders which have equal amount of Cu²⁺ and Mn²⁺ (Cu_0.5Mn_0.5Fe₂O₄). The high catalytic activity of Cu_0.5Mn_0.5Fe₂O₄ can be attributed to the changes of the valence state of catalytically active components of the ferrite powders. The firing temperature plays insignificant role in the catalytic activity of CO over nanocrystallite copper manganese ferrites. The mechanism of catalytic oxidation reactions was studied. It was found that the CO catalytic oxidation reactions on the surface of the Cu _x Mn_1−x Fe₂O₄ was done by the reduction of the ferrite by CO to the oxygen deficient lower oxide then re-oxidation of this phase to the saturated oxygen metal ferrite again.     

Dielectric properties of (1−x)La(Mg1/2Ti1/2)O3–xSrTiO3 ceramics

Powders of (1−x)La(Mg_1/2Ti_1/2)O₃–xSrTiO₃ series have been prepared by a non-conventional chemical route based on the Pechini method. Homogeneous solid solutions allowed the sintering of dense and single-phase ceramics for the full composition range (0⩽x<1). Crystal structure of the ceramics was investigated by XRD and several compositional driven structural transformations were observed. The dielectric function of the ceramics was measured at radio, microwave and far infrared (FIR) frequency ranges to help clarifying the relationship between dielectric properties and structure. The FIR data were found to reflect clearly the sequence of structural modifications observed. In order to evaluate the importance of intrinsic mechanisms in the dielectric response at the GHz and MHz ranges, the reflectivity spectra were fit to the Berreman–Unterwald form of dielectric function. The fits showed that the lower frequency dielectric response seems to be dominated by lattice phonons. Microwave permittivity and temperature coefficient of the resonant frequency were found to obey a hyperbolic-type law.     

Characterization of the Li1−x H x AlO2 system; 0.00 ⩽x ⩽ 0.90

The mechanism of cation replacement in the Li_1–x H _x AlO₂; 0.00 x 0.90 system was investigated with XRD. Examination of the peak position and intensity associated with the 018 and 110 Bragg reflections in a series of partially replaced samples showed that the cation replacement process proceeded by a two phase mechanism. Catalytic characterization of LiAlO₂ with the 2-propanol probe reaction revealed the formation of the condensation products methyl-cyclopentene, 4-methyl-2-pentanone, and 4-methyl-2-pentanol. These products were seen in addition to propylene and acetone. Catalytic characterization of Li_1–x H _x AlO₂;x = 0.90 with 2-propanol showed a significant decrease in condensation activity and no change in the propylene/acetone ratio relative to LiAlO₂. This suggests that the decrease in the amount of lithium eliminated the basic sites necessary for the condensation reactions.     

CaO-MgO-Al2O3-SiO2 corrosion behavior of air-plasma-sprayed (LaxYb1−x)2Zr2O7

The CaO-MgO-Al₂O₃-SiO₂ (CMAS) corrosion of thermal barrier coatings (TBCs) is a crucial problem for the lifetime of blades and vanes of jet engine and gas turbine at high operating temperature. Although many new alternative materials for TBCs have been developed in recent years, their application is limited by the CMAS corrosion. On the other hand, the composition difference of CMAS between regions makes solving this problem very difficult. Therefore, in this study, the yearly composition changes of sand-dust around Beijing area were investigated. The high-temperature corrosion behavior of air-plasma-sprayed 8YSZ and newly developed (La_xYb_1−x)₂Zr₂O₇ TBCs by the representative sand-dust of Beijing was investigated. In comparison, a universally used CaO-riched composition of simulated silicate deposit was also adopted for the TBCs corrosion test. It is found that the (La_xYb_1−x)₂Zr₂O₇ TBCs performs much better anti-corrosion behavior than that of 8YSZ, both by Beijing sand-dust and simulated one. Particularly, Yb₂Zr₂O₇ TBCs appear to be the optimum material against silicate deposits attack. The mechanism of silicate deposits corrosion has also been discussed.     

Composition and pH dependence on aggregation of SiO2–PVA suspension for the synthesis of porous SiO2–PVA nanocomposite

Porous monolithic SiO₂–poly(vinyl alcohol) (PVA) nanocomposites were fabricated by drying an SiO₂–PVA suspension. Depending on the amount of added PVA and pH value of the suspension, the Brunauer–Emmett–Teller surface areas, total pore volumes, and mean pore radii of the (100 ? x)SiO₂–xPVA (x = 0, 10, 20, 30 wt%) nanocomposites were 102–313 m² g^?1, 0.61–1.42 cm³ g^?1, and 8.1–14.7 nm, respectively. Some cracks were observed in the monolithic SiO₂–PVA nanocomposite, affected by the pore size. To elucidate crack generation, the correlation between the dispersion/aggregation in the SiO₂–PVA suspension and the pore size distribution of the nanocomposite was evaluated in terms of the added PVA amount and pH value. At x = 20 and pH 3, the SiO₂ particles and PVA aggregated in the suspension. The preparation of crack-free monolithic SiO₂–PVA nanocomposites was possible using the aggregated suspension owing to the low capillary force during drying because of the relatively large pores.