Solid solutions Na1 - xKxB3O5 (0.5 < x ≤ 1.0)

The phase relations in the NaB₃O₅-KB₃O₅ pseudobinary system are investigated using high-temperature X-ray powder diffraction, differential scanning calorimetry, and the annealing and quenching techniques. Solid solutions Na_{1 - x}K_xB₃O₅ (0.5 < x 1.0) based on the KB₃O₅ phase are found in the system at temperatures below 650–670°C. The replacement of potassium atoms by sodium atoms is accompanied by the contraction of the structure along the a and c axes. The parameter b (the direction of channels in the structure) is insensitive to the substitution of sodium atoms for potassium atoms. No isomorphic miscibility on the basis of NaB₃O₅ is revealed in the system. In the region from 0 to 50 mol % KB₃O₅, there exist two phases, namely, Na_{1 - x}K_xB₃O₅ (x 0.5) and -NaB₃O₅.Original Russian Text Copyright © 2004 by Fizika i Khimiya Stekla, Bubnova, Georgievskaya, Filatov, Ugolkov.     

Electrochemical behaviour of FexCo3?xO4 with (x?=?0, 1, 2 and 3) oxides thin film electrodes in alkaline medium

Spinel-type Fe _x Co_3−x O₄ thin films with x = 0, 1, 2 and 3 were prepared, on stainless steel supports, using the thermal decomposition method at 400 °C. The X-ray diffraction patterns show the presence of a spinel-type structure with a low crystallinity. The electrochemical behaviour was investigated in 1 M KOH, using open-circuit-potential measurements and cyclic voltammetry. The studies allowed to observe the redox reactions occurring at the Fe _x Co_3−x O₄ (x = 1 and 2) oxide surface, namely Fe₃O₄/Fe(OH)₂ or Fe₃O₄/Fe₂O₃, Co₃O₄/CoOOH, Co(OH)₂/CoOOH and CoO₂/CoOOH by comparing the experimental data with those obtained for the Co₃O₄ and Fe₃O₄ films as well as with those referred to in the literature. The results show that iron ions play the major role in the solid-state surface redox transitions in the negative potential range, whereas the cobalt ions are the key species in the positive potential range. However, the contribution of each component, although small, has to be considered in both potential regions.     

Insights into the Reactivity of La1?xSrxMnO3 (x?=?0?÷?0.7) in High Temperature N2O Decomposition

Abstract  

In this paper a wide range of La_1−x Sr _x MnO₃ (x = 0–0.7) perovskites was synthesized by Pechini route, characterized by XRD (including high temperature measurements), XPS, differential dissolution phase analysis, TPR H₂, oxygen exchange and tested in N₂O decomposition at 900 °C. At low degree of Sr substitution for La (x ≤ 0.3), high catalytic activity was found for perovskites with hexagonal structure (x = 0.1–0.2) and can be related to fast oxygen mobility caused by the lattice disordering during polymorphic phase transition from the hexagonal to cubic structure. For multiphase samples (x > 0.3) increase of activity and oxygen mobility can be attributed to the formation of the layer-structured perovskite–LaSrMnO₄ on the surface.     

New anode materials of Li1+xV1?xO2 (0?≤?x?≤?0.1) for secondary lithium batteries: correlation between structures and properties

Li_1+x V_1−x O₂ (0 ≤ x ≤ 0.1) compounds were studied as the anode materials for a lithium-ion battery. The crystal and electronic structures of the prepared materials were correlated with electrical conductivities and electrochemical properties. The electrochemical behaviors were significantly dependent on the composition of Li_1+x V_1−x O₂, and these were resulted from the perturbation of the local electronic structure arising from the increase in lithium contents in Li_1+x V_1−x O₂ rather than from the slight distortion in the crystal structure. The electrical conductivities of Li_1+x V_1−x O₂ increased with the increase in lithium contents in the compounds. Li_1.1V_0.9O₂ and Li_1.075V_0.925O₂ samples exhibit the first discharge capacities of 250 and 241 mAh g⁻¹ at 0.2 C-rate, respectively.     

Direct evidence of oxygen evolution from Li1+ x (Ni1/3Mn1/3Co1/3)1? x O2 at high potentials

Li_1+x (Ni_1/3Mn_1/3Co_1/3)_1−x O₂ (NMC) oxides are among the most promising positive electrode materials for future lithium–ion batteries. A voltage “plateau” was observed on the first galvanostatic charging curve of NMC in the extended voltage region positive to 4.5 V vs. Li/Li⁺ for compounds with x > 0 (overlithiated compounds). Differences were observed in the cycling stability of the overlithiated and stoichiometric (x = 0) NMC oxides in this potential region. A differential plot of the charge vs. potential profile in the first cycle revealed that, for the overlithiated compounds, a large irreversible oxidative peak arises positive to 4.5 V vs. Li/Li⁺, while in the same potential region only a small peak due to the electrolyte oxidation is detected for the stoichiometric material. Differential Electrochemical Mass Spectrometry (DEMS) was used to investigate the high voltage region for both compounds and experimental evidence for oxygen evolution was provided for the overlithiated compounds at potentials positive to 4.5 V vs. Li/Li⁺. No oxygen evolution was detected for the stoichiometric compound.     

Structural and dielectric behavior of yNi1 ? xCdxFe2O4 + (1 ? y)Ba0.8Sr0.2TiO3 magnetoelectric composites prepared through SHS route

The structural and dielectric properties of SHS-produced yNi_{1 − x} Cd _x Fe₂O₄ + (1 − y)Ba_0.8Sr_0.2TiO₃ (x = 0.2, 0.4, 0.6; y = 15, 30, 45%) magnetoelectric composites were characterized by XRD, SEM, and resistivity/dielectric measurements. SEM images reveal that SHS reaction can produce two pure phases simultaneously. The grown Cd-substituted nickel ferrite grains were well dispersed in a BST matrix. A decrease in resistivity with temperature shows the semiconducting nature of synthesized samples. The dielectric results demonstrated an attractive response of dielectric constant to frequency and temperature. The Curie temperature of about 480°C was observed in the Ni_0.4Cd_0.6Fe₂O₄ + Ba_0.8Sr_0.2TiO₃ composite.     

Characterization of MgMnxFe2?xO4 as a possible cathode material for electrochemical reduction of NOx

Spinel-type oxides of MgMn _x Fe_2−x O₄, x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0, were synthesized as a solid state reaction and characterized with dilatometry and resistivity measurements up to 1000 °C. Results showed a general decrease of the linear expansion and an increase in conductivity as a function of the Mn content. Point electrodes were analyzed from 300 to 600 °C in a pseudo-three-electrode setup in 1% NO, 1% NO₂, and 10% O₂ using cyclic voltammetry. The activities in O₂ were in general very low whereas the activities in NO were slightly higher. The activities in NO₂ were for all materials much higher than the activities in O₂. Even though Mn tends to decrease the activity of the materials, current ratios of I_NOx/I_O2I_{{\rm NO}_{x}}/I_{{\rm O}_2} have relatively high values in both NO and NO₂.     

Ionic conductivity of (As2Se3)1 ? x(AgHal)x (Hal = I, Br) nanocomposites

Nanocomposites based on chalcogenide glasses have been synthesized. A differential thermal analysis of (As₂Se₃)_{1 − x} (AgI) _x and (As₂Se₃)_{1 − x} (AgBr)x (0 ≤ x ≤ 0.5) samples has been performed. The size of nanofragments that undergo elementary structural transformations has been evaluated. The data obtained are in agreement with the evaluated sizes of X-ray coherent scattering regions. The electrical properties of the glasses under consideration have been studied using impedance spectroscopy in the temperature range 293–393 K. It has been demonstrated that the ionic component of the electrical conductivity dominates in glasses with a high content of silver halide.     

XPS studies on the oxygen species of LaMn1−xCuxO3+λ

The electronic states of LaMn_1−xCu_xO_3+λ (x=0–0.4) have been studied with X-ray photoelectron spectroscopy (XPS). The valence states of substituted copper ions were Cu²⁺ and the manganese ions were a highly mixed state of Mn³⁺ and Mn⁴⁺. The nonstoichiometry and electronic state of lattice oxygen have been studied. The samples at x=0 and 0.1 had an excess of lattice oxygen but those at x=0.2–0.4 had lattice oxygen deficiency. A modified Auger parameter (Δ′) was used to evaluate the electronic states of oxygen ions. The Δ′ of lattice oxygen increased with increasing substitute quantity. This increase of Δ′ reflected the decrease of ionic bond character of lattice oxygen. The adsorbed oxygen species on LaMn_1−xCu_xO_3+λ was assigned mainly as O⁻ from the peak positions of spectra for the O 1s and O KLL levels, and the Δ′ of this O⁻ decreased with x. This decrease, i.e., the increase of ionic bond character of adsorbed oxygen was correlated well with the value of nonstoichiometry of lattice oxygen.

The rate of CO oxidation at 448 K was increased by the substitution till x=0.4. We consider that this enhancement of reactivity comes from the change of electronic state of adsorbed oxygen, O⁻ itself, i.e., a weak interaction between O⁻ and low coordinated metal site brings about a high reactivity.     

Transformation of the crystal structure in the series of K1 ? xCsxBSi2O6 borosilicate solid solutions

The transformation of the crystal structure by isomorphous K⁺-Cs⁺ substitutions in the non-tetrahedral positions leading to the phase transition has been studied in the series of K_{1 − x} Cs _x BSi₂O₆ solid solutions. The samples have been crystallized from the glass at 850°C for 10 h. According to the data on the crystal structures refined by the Rietveld method, the compositions with 0 ≤ x ≤ 0.35 crystallize in space group I[`4]3dI\bar 43d, structural type KBSi<sub>2</sub>O<sub>6</sub>, and those with 0.37 ≤ x ≤ 1.0, crystallize in Ia[`3]dIa\bar 3d, structural type CsBSi₂O₆. The reversible cubic-cubic phase transition I[`4]3d \rightleftarrows Ia[`3]dI\bar 43d \rightleftarrows Ia\bar 3d occurs in the composition range x = 0.35–0.37.     

On the local structure of Cd3+ centers in (BaGeO3)1 ? x ? y (Al2O3) x (0.45CaF2 · 0.55MgF2) y glasses

A correlation between the ¹⁵⁵Gd M?ssbauer spectra of the GdAlO₃ and Gd₃Al₅O₁₂ compounds and Gd³⁺-doped glasses in the (BaGeO₃)_{1 − x − y} (Al₂O₃) _x (0.45CaF₂ · 0.55MgF₂) _y system is revealed. The conclusion is drawn that, in the structure of the glasses under investigation, trivalent gadolinium atoms form structural units characteristic of mixed gadolinium and aluminum oxides. Original Russian Text ? S.A. Nemov, A.V. Marchenko, P.P. Seregin, 2008, published in Fizika i Khimiya Stekla.     

A study of the formation of Ln2 + xMe2 ? xO7 ? x/2 (Ln = Gd, Dy; Me = Zr, Hf) nanocrystals

It has been established that the process of producing the Ln_{2 + x} Me_{2 − x} O_{7 − x/2} (Ln = Gd, Dy; Me = Zr, Hf) nanocrystals by calcination of hydroxides, which, in turn, have been produced by coprecipitation of metal salts, includes several stages. At the beginning, the X-ray amorphous structure of the precursors remains unchanged during dehydration; during subsequent heating to 600–700°C, nanocrystals with a disordered fluorite structure begin to be formed. An increase in the temperature above 700°C leads to an increase in the size of crystallites (coherent scattering regions). This process is accompanied by changes occurring in their local structure. In the nanocrystalline powders of Cd₂Hf₂O₇ and Gd₂Zr₂O₇ synthesized at 1200°C (6 h), the pyrochlore-type superstructure with the lattice parameters doubled relative to fluorite has been revealed. It has also been found that, possibly, the Dy₂HfO₅ sample at 1600°C (3 h) has a modulated structure.     

Y2O3掺杂TiO2催化超声降解苯胺的研究

选取苯胺为降解目标物,研究了用实验室合成的氧化钇掺杂二氧化钛为催化剂存在下的超声反应,重点考察了超声时间长短、氧化钇的掺杂量、二氧化钛的添加量、溶液初始浓度、溶液pH值对苯胺降解率的影响。实验结果表明,在溶液pH 2.0、苯胺质量浓度为20mg/L、溶液用量50mL、氧化钇掺杂比为0.1%、催化剂用量为0.02g的条件下,用输出功率5.0 W/cm2和频率25kHz的超声波照射80min,苯胺降解率可达93.94%。     

添加Y2O3对CaO-MgO-SiO2体系中CMS的影响

为了提高镁质耐火材料的高温性能,以分析纯化学试剂MgO、CaO、SiO₂、Y₂O₃等为主要原料,研究了添加Y₂O₃对CaO-MgO-SiO₂体系中钙镁橄榄石(CMS)的生成和转化的影响,以及转化生成物Ca₄Y₆O(SiO₄)₆的耐火度。结果表明：1)Y₂O₃的添加不仅能够显著减少CaO-MgO-SiO₂体系中低熔点相CMS的生成量,而且能够从CMS中捕获CaO和SiO₂使CMS转化为高熔点相Ca₄Y₆O(SiO₄)₆、MgO和Y₂Si₂O₇,有利于提高镁质材料的高温性能。2)Ca₄Y₆O(...     

EPR study of solid solutions La1 ? 0.33yBa0.33yMnyAl1 ? yO3 (y = 0.02, 0.04, 0.10)

Solid solutions La_{1 − 0.33y} Ba_0.33y Mn _y Al_{1 − y} O₃ (y = 0.02, 0.04, 0.10) prepared using the ceramic technique have been investigated by the EPR method at temperatures of 77 and 300 K. By comparing with the calculated spectra, the experimental spectra have been assigned to Mn²⁺ ions (g = 2.04 and line width ΔH _pp = 64 × 10⁻⁴ T at T = 77K) and Mn⁴⁺ ions (g = 1.97 and ΔH _pp = 76 × 10⁻⁴ T at T = 77 K) and the broad line (ΔH _pp = 500 × 10⁻⁴ T at T = 77 K) has been attributed to clusters. The dilution of manganese ions as a result of the dissolution of La_0.67Ba_0.33MnO₃ in LaAlO₃ has allowed one to trace the cluster formation and the spin dynamics of Mn ions. It has been established that, at room temperature, compared to the system in which the Sr²⁺ ion with a smaller ionic radius is the replacing element, the localized states are more stable at all three manganese concentrations (the EPR lines are more intense). The La_0.67Ba_0.33MnO₃ clusters dissolved in LaAlO₃ retain some properties of a concentrated compound even upon dilution to y = 0.02.     

Synthesis of LiFe0.4Mn0.6?xNixPO4/C by co-precipitation method and its electrochemical performances

LiFe_0.4Mn_0.6−x Ni _x PO₄/C(x = 0, 0.05, 0.1, and 0.2) composite cathode materials for lithium ion batteries have been prepared by the co-precipitation method using oxalic acid as a precipitator. The structure and morphology of precursors and products have been investigated. Electrochemical tests demonstrate that LiFe_0.4Mn_0.55Ni_0.05PO₄ can deliver a specific capacity of 142 mAh g⁻¹ at 0.1 C, and retains 133 mAh g⁻¹ after 60 cycles. The rate performance of LiFe_0.4Mn_0.6PO₄ is obviously improved by doping Ni. The capacity of LiFe_0.4Mn_0.55Ni_0.05PO₄ at 2 C is 110 mAh g⁻¹.     

Scanning Tunneling Microscopy Study of H6+xP2Mo18?xVxO62 (x?=?0–3) Wells–Dawson Heteropolyacid Catalysts: Correlation of NDR Peak Voltage with Reduction Potential and Oxidation Catalysis

Abstract  

Scanning tunneling microscopy (STM) and tunneling spectroscopy studies were carried out to examine the redox properties of vanadium-containing H_6+x P₂Mo_18−x V _x O₆₂ (x = 0, 1, 2, 3) Wells–Dawson heteropolyacid (HPA) catalysts. The HPAs formed two-dimensional well-ordered monolayer arrays on a graphite surface and exhibited a distinctive current–voltage behavior called negative differential resistance (NDR). The NDR peak voltages of H_6+x P₂Mo_18−x V _x O₆₂ HPAs were correlated with reduction potentials determined by temperature-programmed reduction and with catalytic activity for oxidative dehydrogenation of isobutyraldehyde to methacrolein. The NDR peak voltage of H_6+x P₂Mo_18−x V _x O₆₂ appeared at less negative voltage with increasing reduction potential and oxidation catalysis.     

Depolarization temperature and piezoelectric properties of (Bi1/2Na1/2)TiO3–(Bi1/2Li1/2)TiO3–(Bi1/2K1/2)TiO3 lead-free piezoelectric ceramics

The phase transition temperature and piezoelectric properties of x(Bi_1/2Na_1/2)TiO₃–y(Bi_1/2Li_1/2)TiO₃–z(Bi_1/2K_1/2)TiO₃ [x + y + z = 1] (abbreviated as BNLKT100y–100z) ceramics were investigated. BNLKT100y–100z ceramics were prepared by conventional ceramic fabrication. The depolarization temperature T_d was determined by the temperature dependence of the dielectric and piezoelectric properties. This study focuses on the effect of Li¹⁺ and K¹⁺ ions on T_d and the piezoelectric properties of BNT ceramics. BNLKT100y–100z (y = 0–0.08) has a morphotropic phase boundary (MPB) between rhombohedral and tetragonal phases at z = 0.18–0.20, and high piezoelectric properties were obtained at the MPB composition. The piezoelectric constant d₃₃ increased with increasing y; however, T_d decreased above y = 0.06. The d₃₃ and T_d values of BNLKT4-20 and BNLKT8-20 were 176 pC/N and 171 °C, and 190 pC/N and 115 °C, respectively.     

Multiferroic ceramics in BaO–Y2O3–Fe2O3–Nb2O5 system

Multiferroic ceramics in BaO–Y₂O₃–Fe₂O₃–Nb₂O₅ system were synthesized and their dielectric, ferroelectric and magnetic properties were evaluated. XRD results showed that the ceramic composite consists of a major phase of tetragonal tungsten bronze structured Ba₂YFeNb₄O₁₅, and minor phases of monoclinic YNbO₄ and hexagonal Ba₃Fe₂Nb₆O₂₁. Three dielectric relaxations were observed in the temperature range from 125 to 575 K. The relaxor dielectric behavior in the temperature range from 125 to 350 K was attributed to the random occupation of Fe³⁺ and Nb⁵⁺ ions at B site of the tungsten bronze structure. The electrode polarization and the inhomogeneous structure contributed to the high-temperature and middle-temperature dielectric relaxations, respectively. Both the ferroelectric hysteresis loop and the magnetic hysteresis loop were measured, which suggested that the synthesized ceramic composite was a promising candidate of multiferroics.     

Synthesis and characterization of 5?V LiCoxNiyMn2?x?yO4 (x?=?y?=?0.25) cathode materials for use in rechargeable lithium batteries

Double doped spinel LiCo _x Ni _y Mn_2−x−y O₄ (x = y = 0.25) have been synthesised via sol–gel method using different chelating agents viz., acetic acid, maleic acid and oxalic acid to obtain 5 V positive electrode material for use in lithium rechargeable batteries. The sol–gel route endows lower processing temperature, lesser synthesis time, high purity, better homogeneity, good control of particle size and surface morphology. Physical characterizations of the synthesized powder were carried out using thermo-gravimetric and differential thermal analysis (TG/DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The electrochemical behaviour of the calcined samples has been carried out by galvanostatic charge/discharge cycling studies in the voltage range 3–5 V. The XRD patterns reveal crystalline single-phase spinel product. SEM photographs indicate micron sized particles with good agglomeration. The charge–discharge studies show LiCo_0.25Ni_0.25Mn_1.5O₄ synthesized using oxalic acid to be as a promising cathode material as compared to other two chelating agents and delivers average discharge capacity of 110 mA h g⁻¹ with low capacity fade of 0.2 mA h g⁻¹ per cycle over the investigated 15 cycles.