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.     

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.     

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.     

Magnetic properties of ferrites-cobaltites Bi1 − x La x Fe1 − x Co x O3 (1.0 ≥ x ≥ 0.7) with a perovskite structure

The molar magnetic susceptibility (χ_mol) of Bi_{1 ? x} La _x Fe_{1 ? x} Co _x O₃ solid solutions (x = 1.0, 0.9, 0.8, or 0.7) with a crystal structure of rhombohedrally distorted perovskite (R $\bar 3$ c) has been investigated in the temperature range of 5–300 K in a 0.86 T magnetic field. In the temperature range where χ_mol depends on temperature T according to the Curie-Weiss law, the resulting effective magnetic moments of Fe³⁺ and Co³⁺ ions ( $\mu _{eff,Fe^{3 + } ,Co^{3 + } ,} \mu _{eff,Fe^{3 + } } $ and $\mu _{eff,Co^{3 + } } $ ) have been determined for the solid solutions under study. Fe³⁺ ions in the solid solutions have been found to be in the mixed intermediate spin (IS) and high spin (HS) states ( $\mu _{eff,Fe^{3 + } } $ is 4.26μ_B and 4.68μ_B for the temperature range of 5–100 and 150–300 K, respectively). It is shown that 8% Co³⁺ ions in LaCoO₃ at 5–19 K are in the paramagnetic IS state and they determine to a great extent the magnetic susceptibility. It is established that only 9% and 18% Co³⁺ ions in Bi_{1 ? x} La _x Fe_{1 ? x} Co _x O₃ solid solutions (x = 0.9 or 0.8) are in the paramagnetic IS state in the temperature ranges of 5–30 and 5–110 K, respectively, while the other ions are diamagnetic.     

Crystal structure,magnetic and electric properties of highly coercive ferrites Sr1 − x Sm x Fe12 − x Zn x O19 (0 ≤ x ≤ 0.4)

The samples of highly coercive ferrites Sr_{1 ? x} Sm _x Fe_{12 ? x} Zn _x O₁₉ (0 ≤ x ≤ 0.4) with the structure of magnetoplumbite have been obtained by the solid-phase method. It has been determined that the samples Sr_{1 ? x} Sm _x Fe_{12 ? x} Zn _x O₁₉ are single-phase at x ≤ 0.2 and contain the impurity phases of α-Fe₂O₃, SmFeO₃, and ZnFe₂O₄ at x ≥ 0.3. In the magnetic fields up to 14 T, the specific magnetization has been measured and the values of coercive force (_σ H _c ) have been determined at 5 and 300 K. It has been shown that semiconductor electroconductivity of single-phase samples Sr_{1 ? x} Sm _x Fe_{12 ? x} Zn _x O₁₉ gradually decreases with the increase in the degree of substitution of x from 0 to 0.2.     

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.     

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.     

Preparation of La1?x Sr x CoO3 Oxide Electrode Material and its Influence on the Structure and Dielectric Performance of the Supported Ba1?x Sr x TiO3 Thin Films

Using the sol–gel method, La_1−x Sr _x CoO₃ (LSCO) electrode films were first fabricated on the Si (100) substrates, followed by the growth of Ba_1−x Sr _x TiO₃ (BST) thin films on the LSCO electrode film. The crystal structure and surface morphology of these films were characterized by XRD and SEM. The effects of Sr-doping and annealing temperature on the structure and electric resistivity of the LSCO films and the dielectric properties of the BST films were studied. Results show that the La_0.5Sr_0.5CoO₃ electrode annealed at 750 °C has the lowest electric resistivity, 1.1 × 10⁻³Ω cm. The relative permittivity of the La_0.5Sr_0.5CoO₃-supported BST films first increases and then decreases with Sr-doping. The relative permittivity of the BST film decreases while the dielectric loss increases with frequency. Among the studied BST films, Ba_0.5Sr_0.5TiO₃ has the largest relative permittivity and the smallest dielectric loss (95 and 0.1, respectively) when the frequency is 1 kHz.     

Surface Exchange of Oxygen in La1−x Sr x FeO3−δ (x = 0, 0.1)

The electronic charge carrier concentration in La_1?x Sr _x FeO_3?δ was shown to depend on the partial pressure of O₂ (pO ₂). Chemical diffusion coefficient and surface exchange coefficient, k _chem, were determined by conductivity relaxation in O₂/N₂ and CO/CO₂ mixtures. k _chem was proportional to pO ₂ ^1.06 in O₂/N₂, while in CO/CO₂ k _chem was controlled by a reaction mechanism involving both CO and CO₂.     

Synthesis,characterization and catalytic properties of La2−x Sr x NiO4−δ

Various compositionsx in the catalyst system La_2–x Sr _x NiO_4– have been prepared by conventional techniques and characterized by X-ray powder diffraction, electron microscopy and BET surface measurements. The catalytic properties of these catalysts have been tested in the propylene oxidation reaction. The catalytic activity can be correlated with the oxygen content and with the strontium substitution.     

LaCo1−x Pd x O3 Perovskite-Type Oxides: Synthesis, Characterization and Simultaneous Removal of NO x and Diesel Soot

A series of naometric perovskite catalysts LaCo_1?x Pd _x O₃ (x = 0, 0.01, 0.03) were prepared via a solution combustion synthesis route using metal nitrates as oxidizers and urea as fuel. It is essential to add a certain amount of ammonia aqueous solution to Pd²⁺ ions solution in the catalyst preparation process. Homogeneous nanoparticles LaCo_1?x Pd _x O₃ catalysts with the sizes in the range of 68–122 nm were obtained and characterized by using of XRD, BET, H₂-TPR, XPS, SEM and TEM. Pd was successfully introduced into the LaCoO₃ perovskite lattices. Further information was obtained by using XPS upon the LaCo_0.97Pd_0.03O₃ (with NH₄OH) sample after H₂-TPR. The results revealed that surface Pd was reduced to the metallic state at the end of the first step in the H₂-TPR experiment, and some surface Co could be reduced to metallic Co simultaneously. The catalytic properties were investigated for simultaneous NO _x -soot removal reaction. The performance of LaCo_1?x Pd _x O₃ catalysts were greatly improved by the partial substitution of Pd. The maximum NO conversion into N₂ and the ignition temperature of soot are 32.8% and 265 °C, respectively.     

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.     

A Comparison of Catalytic Properties of Cs x H3−x PW12O40 Salts of Various Cesium Contents in Gas Phase and Liquid Phase Reactions

The cesium salts Cs _x H_3?x PW₁₂O₄₀ of Cs content x = 2 up to x = 3 were tested as the catalysts in the gas and liquid phase reactions. Dehydration of ethanol and transesterification of triglycerides with methanol were selected as the catalytic reactions. Apart from the standard preparation, the catalysts were prepared by two-stage procedure with methanol or water as a solvent. The Cs-salts were characterized by FT-IR, XRD, scanning electron microscopy and energy dispersive X-ray techniques. In turn, the influence of Cs-salts composition on the pH and conductivity of their aqueous colloidal solutions was investigated. The results obtained by the latter techniques were also characteristic for acidity of surface layer of colloidal particles because of surface layer-solution equilibrium. It has been shown that the secondary structure of acidic cesium salts existing in crystalline samples (solid solution of H₃PW₁₂O₄₀ in Cs₃PW₁₂O₄₀) changes after contacting with polar medium to the system consisting most probably of Cs₃PW₁₂O₄₀ core with epitaxial layer of heteropolyacid. This is result of the protons migration from bulk to surface layer of primary particles enhanced by polar medium. It strongly influences the surface acidity of primary particles as well as the activity of Cs-salts in transesterification of triglycerides with methanol. In such polar medium, Cs₂HPW₁₂O₄₀ salt becomes the most active catalyst, more active than Cs_2.5H_0.5PW₁₂O₄₀. An accumulation of partial glycerides and in particular glycerol on the surface of primary particles of Cs-salts resulted in relatively low maximum conversion of triglycerides, most probably due to partial blockage of the catalytic centers. This effect and the almost constant activity of Cs-salts under recycling use in the transesterification experiments are considered to be experimental evidences that methanolysis over Cs-salts was accomplished with the participation of surface protons.     

Composition dependence of the oxygen-evolution reaction rate on Ir x Ti1−x O2 mixed-oxide electrodes

Mudcrack-free oxide films of Ir _x Ti_1–x O₂ (0 < x 1) on titanium substrates were obtained, and the effects of the oxide composition on the rate of oxygen-evolution reaction were investigated. At x 0.6, Ir-rich grains appear on the mudcrack-free surface. In the purely single-phase region (0 < x 0.5), the pseudo-capacitive charge is proportional to the surface composition, x _s, and the exchange-current density for the oxygen-evolution reaction increases linearly with x _s at 0.2 x _s 0.5, with an extrapolated intercept at x _s 0.15, below which the oxides are inactive.     

Acid Strength of H3PW x Mo12−x O40 and H6P2W x Mo18−x O62 Heteropolyacid Catalysts as a Probe of Acid Catalysis for 2-Propanol Conversion Reaction

Acid strength of H₃PW _x Mo_12?x O₄₀ (x = 0, 3, 6, 9, and 12) Keggin heteropolyacid (HPA) and H₆P₂W _x Mo_18?x O₆₂ (x = 0, 3, 9, 15, and 18) Wells-Dawson HPA catalysts was determined by NH₃-TPD measurements. Desorption peak temperature (acid strength) of H₃PW _x Mo_12?x O₄₀ and H₆P₂W _x Mo_18?x O₆₂ catalysts showed the same trend with respect to tungsten substitution, and increased with increasing tungsten substitution in both families of HPA catalysts. In order to correlate the acid strength with the acid catalysis of HPAs, vapor-phase 2-propanol conversion reaction was carried out as a model reaction. Yield for propylene (a product formed by acid catalysis of HPA) increased with increasing tungsten substitution and with increasing desorption peak temperature (acid strength) across both HPA families, regardless of the identity of HPA catalyst (without HPA structural sensitivity). The acid strength of H₃PW _x Mo_12?x O₄₀ and H₆P₂W _x Mo_18?x O₆₂ catalysts could be utilized as a probe of acid catalysis for 2-propanol conversion reaction.     

Effect of Composition on Electrical and Optical Properties of Thin Films of Amorphous GaxSe100?x Nanorods

We report the electrical and optical studies of thin films of a-Ga _x Se_100−x nanorods (x = 3, 6, 9 and 12). Thin films of a-Ga _x Se_100−x nanorods have been synthesized thermal evaporation technique. DC electrical conductivity of deposited thin films of a-Ga _x Se_100−x nanorods is measured as a function of temperature range from 298 to 383 K. An exponential increase in the dc conductivity is observed with the increase in temperature, suggesting thereby a semiconducting behavior. The estimated value of activation energy decreases on incorporation of dopant (Ga) content in the Se system. The calculated value of pre-exponential factor (σ₀) is of the order of 10¹ Ω⁻¹ cm⁻¹, which suggests that the conduction takes place in the band tails of localized states. It is suggested that the conduction is due to thermally assisted tunneling of the carriers in the localized states near the band edges. On the basis of the optical absorption measurements, an indirect optical band gap is observed in this system, and the value of optical band gap decreases on increasing Ga concentration.     

Surfactant-Controlled and Microwave-Assisted Synthesis of Highly Active Ce x Zr1−x O2 Nano-Oxides for CO Oxidation

Uniform nanosized, mesoporous and high specific surface area ceria–zirconia (1:1 mole ratio) solid solutions were synthesized employing a poly-block copolymer surfactant combined with microwave or thermal treatment. For comparison purpose an identical composition Ce _x Zr_1?x O₂ mixed oxide was also prepared by a conventional coprecipitation method. The surface and bulk structure of the synthesized samples were investigated using X-ray diffraction (XRD), small angle X-ray scattering (SAXS), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), BET surface area and BJH pore size distribution (PSD) methods. The catalytic activity was evaluated for CO oxidation at normal atmospheric pressure. The Ce _x Zr_1?x O₂ solid solutions obtained through surfactant use exhibited high specific surface area and mesoporosity. The XRD measurements revealed the presence of cubic Ce_0.75Zr_0.25O₂ and Ce_0.6Zr_0.4O₂ phases in the case of conventional coprecipitation and surfactant controlled synthesized samples, respectively. The Raman measurements revealed existence of more oxygen defects in the surfactant-controlled and microwave treated sample. The SEM images suggested that all samples consist of typical spherical agglomerates with almost uniform size within the nanometer size range. The TEM measurements revealed nanosized crystallites in a narrow range between 4 and 8 nm, and densely packed in the case of conventional precipitation and microwave treated samples. Interestingly, the Ce _x Zr_1?x O₂ solid solution obtained by surfactant-controlled method and treated with microwave radiation exhibited better CO oxidation activity than other samples. Enhanced activity of surfactant-controlled and microwave treated sample is correlated with its unique physicochemical characteristics.     

Efficient and selective oxidation of olefins and alcohols using nanoparticles of WO3-supported manganese oxides (W1−x Mn x O3)

Nanoparticles of manganese oxide supported on tungsten oxide (WO₃) were synthesized by an impregnation method using Mn(NO₃)₂ and Na₂WO₄ as a source of manganese and tungsten. Atomic absorption spectroscopy (AAS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the physicochemical properties of compounds. Due to a highly dispersed state of manganese or insertion of manganese ions into the WO₃ lattice, no manganese oxide peak was observed in the XRD patterns of the W_1?x Mn _x O₃ nanoparticles. Investigation of W_1?x Mn _x O₃ by AAS and EDX showed that the relative atomic abundance of Mn present in the bulk and on the surface of WO₃ was 3.68% and 4.8% respectively. For the first time, the catalytic oxidation of olefins and alcohols, in the presence of these materials and hydrogen peroxide (H₂O₂) as a green oxidant at room temperature was studied. The recoverability and catalyst leaching of the W_1?x Mn _x O₃ nanoparticles in epoxidation of styrene as a model reaction were also investigated.     

Thermal characterization of Se78 − x Te20Sn2Pb x (0 ≤ x ≤ 6) glassies for phase change optical recording technique

New multi-component glasses of Se_{78 ? x} Te₂₀Sn₂Pb _x (0 ≤ x ≤ 6) system have been synthesized using melt-quench technique. Differential Scanning Calorimetric measurements are performed at different heating rates under non-isothermal conditions to study the glass transition kinetics of prepared chalcogenide glass. Different kinetic parameters such as the activation energy of glass transition, thermal stability, glass forming ability etc have been determined. The composition dependence of kinetic parameters of glass transition is also discussed.