Electrochemical behavior of CoSb<Subscript>3</Subscript> in sulfuric and oxalic acids over the potential range 0 to 40 V

The electrochemical behavior of pure Co, pure Sb, and CoSb₃ has been investigated over a large anodic potential range (0 to 40 V) in two acids, i.e., oxalic acid or sulfuric acid at different concentrations (0.01 to 1 M). Potentiodynamic polarizations performed on CoSb₃ plates reveal the possible formation of a passive layer between 1 and 3 V (vs SCE), on a passivation plateau. The oxidation of CoSb₃ at 2 V in sulfuric and oxalic acids results in the growth of an anodic conversion layer. This coating is mainly made of a porous layer of amorphous antimony oxides due to dealloying of CoSb₃. In the specific case of oxalic acid, rods of crystallized oxalates are tangled between the oxide sheets.     

Studies on thermal decomposition and oxidation of CoSb<Subscript>3</Subscript>

Thermal durability of CoSb₃ in vacuum, helium and air was investigated over the temperature range of 20–850 °C. A scanning electron microscope (SEM) and X-ray powder diffraction technique were used to investigate the microstructure and to carry out the phase analysis of the degradation products. The analysis of a non-isothermal and isothermal decomposition and oxidation of the CoSb₃ powders and polycrystalline samples were performed using simultaneous TG/DTA technique. More detailed studies were carried out on the oxidation in the temperature range 400–600 °C. It was established that the decomposition products are CoSb₂ and a volatile antimony. In case of oxidation a complex three-layered scale is formed, consisting of CoSb₂O₄, CoSb₂O₆ and Sb₂O₄ layers. Both the decomposition and the oxidation kinetics are determined by a diffusion through the growing layers of products. The electrical resistivity and Seebeck coefficient measurements have been also performed on pure and oxidized samples, which showed a large influence of the oxidation on the electrical properties.     

Multiband Transport in CoSb3 Prepared by Rapid Solidification

Nano‐grained CoSb₃ was prepared by melt‐spinning and subsequent spark plasma sintering. The phonon thermal conductivity of skutterudites is known to be sensitive to the kind and the amount of guest atoms. Thus, unfilled CoSb₃ can serve as model compound to study the impact of a nanostructure on the thermoelectric properties, especially the phonon thermal conductivity. Therefore, a series of materials was prepared differing only by the cooling speed during the quenching procedure. In contrast to clathrates, the microstructure of meltspun CoSb₃ was found to be sensitive to the cooling speed. Although the phonon thermal conductivity, studied by means of Flash and 3ω measurements, was found to be correlated with the grain size, the bulk density of the sintered materials had an even stronger impact. Interestingly, the reduced bulk density did not result in an increased electrical resistivity. The influence of Sb and CoSb₂ as foreign phase on the electronic properties of CoSb₃ was revealed by a multi‐band Hall effect analysis. While CoSb₂ increases the charge carrier density, the influence of the highly mobile charge carriers introduced by elemental Sb on the thermoelectric properties of the composite offer an interesting perspective for the preparation of efficient thermoelectric composite materials.     

Structural stability of MnO2 polymorphs and their reactivity vs. lithium

This paper describes the stability of dioxide structures, with ccp and hcp anion arrays, on cycling in lithium cells. Application of a regular solution formalism to transition metal dioxides has led to a potential-composition dependence, which is analogous to that derived from the lattice gas model. However, the present model offers a more integrated approach; it has been found a relationship between stability of MeO₂ (Me=transition metal) polymorphs and their reactivity vs. lithium. On this ground, it has been explained why ternary oxides LiMeO₂ attain a higher potential in relation to lithium than binary oxides MeO₂. Structural modifications of initial electrode materials MeO₂ and LiMeO₂ and their influence on charge/discharge curves have been also investigated. Validity of presented considerations has been verified for different polymorphs of MnO₂.     

Transition probabilities for the ionization of N2, O2, NO and CO molecules

Franck–Condon factors are presented for the normal and stable isotope-labelled N₂, O₂, NO and CO molecules for transitions to the observed ionized states by using the Rydberg–Klein–Rees (RKR ) potential energy curves of the various electronic states involved. It has been observed that for some transitions, the Franck–Condon factors based on the RKR potential energy curves differ appreciably from those based on the Morse potential function. The effect of isotopic substitution on the transition probabilities is also quite significant in a number of cases.     

SAXS study of polymer adsorption on porous ZrO2

The small‐angle X‐ray scattering method (SAXS) has been used for the analysis of polymer adsorption on porous ZrO₂. Particular attention has been paid to the adsorption of polyacrylic acid (PAA) and polyacrylamide (PAM) on the surface of porous ZrO₂. It has been established that the SAXS method determines whether the polymer has penetrated the carrier's pores, and that polymers of low molecular weight create a thin transition layer on the surface of ZrO₂ (understood in the context of a change in the electron density). The creation of this layer is clearly reflected in the run of SAXS curves (Porod's plot). Ruland–Vonk's method has been used to determine the thickness of the transition layer. The results are consistent with those obtained when the viscosity method was used. Copyright © 2003 John Wiley & Sons, Ltd.     

不同取向的CoSb3纳米线阵列的电化学法制备

近年来,金属纳米线及其阵列由于其新奇的物理和化学特性和在纳米器件方面潜在的应用前景,越来越受到人们的关注。氧化铝模板合成一维纳米材料具有设备简单、制作方便等优点,因而成为近年来人们常用的一种方法。利用电化学沉积的方法在多孔氧化铝模板中沉积各种成分的纳米线已成为纳米材料制备的一种常见的方法。这种方法不仅可以得到大面积有序的纳米线阵列,还可以根据需要调节孔洞的大小来控制纳米线的直径[1￣3]。最近理论研究结果预言[4￣6],由于纳米材料的量子限域效应,热电材料的纳米线将有比其相应块体材料更高的品质因数n,这极大地激…     

The electronic structure of ArF and Ar2F

Calculations have been performed on the electronic structure, potential energy curves and radiative transition probabilities of ArF and Ar₂F. Our predicted emission spectra for ArF indicates that only the B²Σ⁺_{$\text{1}\text{2}$} → X²Σ⁺_{$\text{1}\text{2}$} transition exhibits a large transition moment and hence a short (≈5 ns) radiative lifetime. Calculations for Ar₂F indicate that the bound upper ionic state has ²B₂ symmetry with ArAr and ArF bond lengths similar to those in the corresponding diatomic species. The terminating state also has ²B₂ symmetry and this polyatomic system should exhibit a relatively long radiative lifetime (≈200 ns)     

A study of the phase behaviour of metal-free phthalocyanine in a differential scanning calorimeter

The phase behaviour of metal-free phthalocyanine (H₂Pc) has been studied in a differential scanning calorimeter. The effect of the thermal history of samples on the DSC curves was investigated to obtain data concerning the phase transition which appeared on α as well as β forms of H₂Pc over the termperature range from 250 to 340 K. To characterize the α metal-free phthalocyanine at low temperatures, the capacitance of an Ag(H₂Pc)Al sandwich was measured as a function of the temperature. The specific heats of the α and β forms of H₂Pc and the heat of the α → β polymorphic transition were measured. Kinetic parameters of the α → β polymorphic transition have been derived from the calorimetric results.     

Phase transitions in ferroic crystals of KMPO4(M=Fe2+, Co2+, Ni2+) studied by ODSC

The influence of the temperature program parameters of an ODSC experiment on the calculated “reversing” and “kinetic” signals has been studied. Mixed orthophosphate salts of KMPO₄ (where M=Ni²⁺, Co²⁺ and Fe²⁺) which present at least one structural phase transition have been used for this purpose. On these crystalline compounds we have shown that the non reversing heat flow is partly associated with the formation and disappearance of ferroelastic and ferroelectric domain walls. However a proper choice of the temperature program parameters is important so that the calculated “reversing” and “kinetic” curves have the supposed physical meaning according to the assumptions made for the calculations.     

Electron energy loss spectroscopy (EELS) of H2O,H2S,H2Se and H2Te

Electronic excitation in H₂O, H₂S, H₂Se and H₂Te molecules has been studied by the EELS technique. Spectra of H₂S and H₂Se are remarkably similar with the 1b₁-nd transition most intense. The intensity of the first transition 1b₁-nsa₁ decreases through H₂O to H₂Se and this transition is absent in H₂Te. Transitions observed by EELS have been compared with optical absorption studies. A correlation diagram of the occupied and the excited states has been provided for these four molecules by making use of UVPES and EELS.     

Potential energy curves and spectral properties for electronic states of F2 and F+2

Potential energy (PE) curves for the Rydberg states of F₂, and for the ground and lowest two electronic states each of symmetry ²Π_g,u, ²Δ_g,u and ²Σ^±_g,u of F⁺₂, have been obtained using modest-sized configuration-interaction calculations. These PE curves have been used to calculate spectroscopic constants for the electronic states and the results agree reasonably well with the limited experimental and theoretical results previously reported. The theoretical PE curves for the Rydberg states of F₂ are found to be strongly perturbed by valence-Rydberg-ionic interactions and these perturbations appear to be responsible for certain features in recently reported electron energy-loss spectra in F₂. The corresponding electronic wavefunctions have been used to calculate the electronic transition moment, as a function of the internuclear distance, for dipole-allowed transitions between the lowest excited electron state of each symmetry and the appropriate ground electronic state. The radiative emission probabilities, natural lifetimes, and absorption oscillator strengths, for each band system, are also reported here. The predicted lifetimes for vibrational levels of the A ²Π_u of electronic state in F⁺₂ vary from 1.3–1.5 μs and agree reasonably well with the single available set of measurements. The predicted radiative lifetimes for the higher electronic states of F⁺₂ are substantially longer and fall into the range 5–100 ms.     

Thermochemistry study on H2O/NaY zeolite adsorption system

By using an automatic adiabatic calorimeter the heat capacity measurements in the temperature range of 220—320K for H₂O/NaY zeolite adsorption system with various amounts of adsorbed water have been made. In c_p-T curves obtained, there is no peak for solid-liquid phase transition of the adsorbed water. But for H₂O-NaY zeolite system which consists of a saturated H₂O/NaY adsorption system mixed mechanically with a certain amount of water, there are distinct peaks in their c_p-T curves. The peak in the c_p-T curve disappeared as soon as the mixed water in the latter system was evacuated. The facts mentioned above have been discussed from the point of view of the structure of the adsorbed layer and the pore size of zeolite.     

Size‐ and Interface‐Modulated Metal–Insulator Transition in Solution‐Synthesized Nanoscale VO2‐TiO2‐VO2 Heterostructures

The M1 form of vanadium dioxide, which exhibits a reversible insulator–metal transition above room temperature, has been incorporated into nanoscale heterostructures through solution‐phase epitaxial growth on the tips of rutile TiO₂ nanorods. Four distinct classes of VO₂‐TiO₂‐VO₂ nanorod heterostructures are accessible by modulating the growth conditions. Each type of VO₂‐TiO₂‐VO₂ nanostructure has a different insulator–metal transition temperature that depends on the VO₂ domain sizes and the TiO₂‐VO₂ interfacial strain characteristics.     

Phase Transition Originating from Order–Disorder Transformations of Carboxy Oxygen Atoms Coupled with Dynamic Proton Motions in [PhCH2NH(CH3)2]2C2O4⋅H2C2O4

A new molecular phase transition material, [PhCH₂NH(CH₃)₂]₂C₂O₄?H₂C₂O₄, which undergoes a reversible phase transition at 151.6 K, has been successfully synthesized. Differential scanning calorimetry (DSC), specific heat capacity, and dielectric measurements confirm its reversible phase transition with a large thermal hysteresis of 15.1 K, demonstrating that the phase transition is typical first order. Variable‐temperature single‐crystal X‐ray diffraction analyses reveal that the order–disorder transformations of carboxy oxygen atoms induce the structural phase transition. A slight reorientation of the oxalic acid unit is discovered to accompany the ordering of carboxy oxygen atoms at low temperature. The DSC measurement result of the deuterated analog is different to that of 1 , indicating that proton dynamic motions in hydrogen bonds also contribute to the phase transition.     

57Fe Mössbauer spectroscopic and magnetic study of a spin-crossover polymer complex, Fe(3-chloropyridine)2Ni(CN)4

The coordination polymer Fe(3-chloropyridine)₂Ni(CN)₄ (2) has been prepared by a method similar to that for Fe(pyridine)₂Ni(CN)₄ (1). The complex (2) has been characterized by⁵⁷Fe Mössbauer spectroscopy and a SQUID technique.⁵⁷Fe Mössbauer and magnetic susceptibility data show that complex (2) exhibits spin-crossover behavior. The spin transition of (2) occurs between 120 and 80 K with very small hysteresis or without hysteresis. The temperature range of the spin transition in (2) is lower than that in (1). A residual high spin iron(II) fraction is observed at low temperatures in (2), being different from (1). SQUID data also show that samples treated differently yield different spin transition curves.     

On the role of TiO<Subscript>2</Subscript> nanoparticles on thermal behavior of flexible polyurethane foam sandwich panels

A series of flexible polyurethane foam (FPUF) and monolithic polyurethane (PU) sandwich panels reinforced with different contents of TiO₂ nanoparticles (0, 0.5 and 1 mass%) have been successfully prepared by compression molding process at room temperature. The influence of TiO₂ nanoparticles on the thermal properties of PU matrix has been investigated by thermogravimetric and dynamic mechanical thermal analysis (DMTA). The morphology of porous structure of FPUF sandwich panels has been characterized by scanning electron microscopy. The presence of TiO₂ nanoparticles as reinforcement has improved the thermal properties of the FPUF and PU sandwich panel samples. It has been observed that FPUF and PU sandwich panel reinforced with 1 mass% of TiO₂ nanoparticles possessed the highest enhancement in thermal properties in all accomplished thermal tests. The DMTA results for the FPUF and PU sandwich panel reinforced with 1 mass% of TiO₂ nanoparticles indicated that the storage modulus and loss modulus have increased about 1.22 and 1.25 times, 1.5 and 1.55 times, respectively, compared to pure samples. Furthermore, the glass transition (T _g) obtained from the damping factor (tanδ) curves has increased 2 and 1 °C for FPUF and PU sandwich panels, respectively.     

Reaction mechanism and thermoelectric properties of In0·22Co4Sb12 prepared by magnesiothermy

The magnesioreduction synthesis of In_0·22Co₄Sb₁₂ with high In rattler concentration from Sb₂O₄ and In-doped Co₃O₄ precursors is reported. This process directly yields a submicronic powder in a single step of 96 h at 810 K. The reaction mechanism has been investigated by stopping the reaction every 12 h and quantifying the existing phases by X-ray diffraction and Rietveld refinements. The precursors are first reduced in CoO and Sb₂O₃ lower oxides, then form CoSb₂O₆ and CoSb₂O₄ intermediates which are finally reduced in In_xCo₄Sb₁₂. A powder with 350 nm average size and mostly composed of In-filled skutterudite phase with composition close to In_0·17Co₄Sb₁₂ is obtained. Upon spark plasma sintering, small residual amount of InSb reacts with the skutterudite matrix to form a single-phase densified pellet with composition close to In_0·22Co₄Sb₁₂. The resulting densified material with 1.8 μm average grain size shows a figure of merit ZT_max of 0.95 at 750 K.     

ESR studies of heterogeneous radiation processes in a B2O3 + H2O system

The accumulation of radiation-induced defects and of H-atoms on γ-irradiation of a B₂O₃ + H₂O system, at 77K, at different concentrations of water molecules have been investigated by ESR. The radiation-chemical yields of paramagnetic centres and of H-atoms have been determined from appropriate kinetic curves. It has been established that increasing the concentration of water molecules in the system results in a lowering of the yield of paramagnetic centres and an increase in the H-atom concentration. On the basis of the results obtained a mechanism has been suggested for heterogeneous radiation processes in this system at 77 K.     

Magnetocaloric effect in the ternary DyCo3B2 compound

A large magnetocaloric (MCE) effect has been observed for the ternary compound DyCo₃B₂. This material shows the magnetic ordering below T_C = 22 K for H = 0 T. MCE has been determined based on the isothermal magnetization curves measurements and the isomagnetic heat capacity dependence on temperature. The maximum magnetic entropy change −ΔS_M = 17.5 J kg⁻¹K⁻¹ and the adiabatic temperature change ΔT_ad = 14 K have been observed in the neighborhood of the magnetic phase transition at the magnetic field change of 9 T. The analysis of the magnetic contribution to the specific heat indicates on the important role of the crystal electric field and the anisotropy for the properties of the DyCo₃B₂ compound.