Structural investigation on the stoichiometry of β-PdHx in Pd/SiO2 catalysts as a function of metal dispersion

Structural investigations of dispersed Pd/SiO₂ catalysts were carried out with XRD and SAXS techniques, supported by TPR and CO chemisorption measurements. The stoichiometry of Pd hydride, -PdH_x, was determined by measuring the shift of Pd 111 XRD reflection in the presence of hydrogen. It was confirmed thatx decreases when the metal dispersion increases. This behaviour could be quantified up to about 0.45 of Pd dispersion since the angular position of XRD peaks cannot be determined with the necessary precision at higher dispersions. TPR data, obtained up to dispersions of about 0.6, confirms such behaviour. The -PdH_x stoichiometry versus Pd dispersion relationship substantially agrees with that found with other techniques by Boudart and Hwang.     

反硝化除磷的生物化学代谢模型

基于Delft科技大学和活性污泥法动力学模型（ASM2D）推出的反硝化除磷生物化学代谢模型，从生物除磷的计量学和动力学两方面介绍了反硝化除磷过程一系列复杂的生化反应机理。反硝化除磷与传统好氧除磷的生化反应机理非常相似，两种除磷模式的许多化学计量学和动力学方程可以通用；好氧除磷动力学所涉及的一部分参数同时也适用于反硝化除磷动力学；两者最大的区别就是氧化单位NADH2所吸收的磷酸盐量（P／NADH2）不同。引起两者P／NADH2值不同的最根本原因在于：以氧气作为电子受体和以硝态氮作为电子受体，消耗单位NADH2所产生的ATP量不同。在An／ASBR反硝化除磷系统中，测得该值为1．0molATP／molNADH2，此值较An／OS-BR型好氧吸磷系统降低了40％左右。     

近化学计量比SiC陶瓷纤维先驱体制备方法

近几年来，近化学计量比SiC陶瓷纤维的制备已成为SiC陶瓷纤维领域中的热点．PMS和PSE是制备近化学计量比SiC陶瓷纤维的两种先驱体，其制备是得到近化学计量比SiC陶瓷纤维的关键．因此本文综述了近化学计量比SiC陶瓷先驱体的制备方法，包括脱卤合成、MeSiH3的催化脱氢偶合、H3SiH2SiCH3的脱氢偶合、Bu4PCl催化氯硅烷重分配反应等，同时也简评了国内的发展。     

Criteria for Diffusion by a Site-Interchange Mechanism

Criteria are established for evaluating whether self-diffusion in a material may be occurring by a site-interchange diffusion mechanism. The criteria include comparisons between defect formation and migration energies for the site-interchange model and a normal vacancy diffsion model. These criteria are applied to some material systems to illustrate their utility. A site-interchange diffusion mechanism is probably occurring in lithium niobate, but this mechanism is not operative in silicon carbide or in some III-V compound semiconductors.     

Enhanced intrinsic permittivity and bulk response in Y2/3Cu3Ti4+xO12 ceramics

Considering the contribution of the mixed valence structure of Ti³⁺ and Ti⁴⁺ to the semiconductivity of grain, compositions with the formula of Y_2/3Cu₃Ti_4+xO₁₂ were designed and prepared. The dielectric bulk responses of Y_2/3Cu₃Ti_4+xO₁₂ ceramics were explored in detail. Changing Ti stoichiometry gives rise to an increase of the intrinsic permittivity. Y_2/3Cu₃Ti_3.925O₁₂ ceramic exhibits a higher intrinsic permittivity of ~120 at 60 MHz than that of pure Y_2/3Cu₃Ti₄O₁₂ ceramics (87 at 60 MHz). Additionally, the activation energies of bulk responses are significantly enhanced by changing Ti stoichiometry, which is closely linked with the increase of Ti³⁺/Ti⁴⁺.     

Phase structure and electrochemical properties of melt-spinning alloy Zr(MnVNi)_(2.4)

1　INTRODUCTIONItiswellknownthatZr basedAB2 LavesphasealloyelectrodeshavehigherdischargecapacityandmuchbettercyclingstabilitythanthatofAB5alloysalthoughitisexpensivecomparedtoAB5alloys .HowtofurtherimprovetheratioofpropertiesandpriceofAB2 alloyshasbeendrawingtheinterestofmanyin vestigators .Someinvestigationsrevealedthatover stoichiometricAB5typealloyshadbettercharge dis chargecyclingstabilitythanstoichiometricalloys[15] ,andsomeover stoichiometricAB2 typealloysshowedhigherdischargec…     

De‐densification mechanisms of yttria‐doped cerium oxide during sintering in a reducing atmosphere

The presence of residual carbon in oxides in which the valence state can change during sintering may lead to de‐densification or swelling phenomena during the last stage of sintering. This was demonstrated by sintering a Ce_0.85Y_0.15O_2‐x powder compact with or without added graphite carbon in a reducing atmosphere (Ar/5 vol.% H₂) at 1450°C. The shrinkage behavior was studied with a dilatometer combined with an oxygen probe and a gas chromatograph to analyze the composition of the released gases. Oxide reduction during sintering leads to a significant release of oxygen. This oxygen can react with carbon to form gaseous species such as CO. These gases can be released during the second stage of sintering, that is, when the porosity is still open, but they can be trapped in the closing pores during the final stage of sintering. This causes the pressure to increase in the pores, resulting in irreversible swelling, cracking and eventually pellet fracture.     

Oxygen Stoichiometry Effect on Polar Properties of LaAlO3/SrTiO3

Discovery of a ferroelectric‐like behavior of the LaAlO₃/SrTiO₃ (LAO/STO) interfaces provides an attractive platform for the development of nanoelectronic devices with functionality that can be tuned by electrical or mechanical means. However, further progress in this direction critically depends on deeper understanding of the physicochemical mechanism of this phenomenon. In this report, this problem by testing the electronic properties of the LAO/STO heterostructures with oxygen stoichiometry used as a variable is addressed. Local probe measurements in conjunction with interface electrical characterization allow to establish the field‐driven reversible migration of oxygen vacancies as the origin of the ferroelectric‐like behavior in LAO/STO. In addition, it is shown that oxygen deficiency gives rise to the formation of micrometer‐long atomically sharp boundaries with robust piezoelectricity stemming from a significant strain gradient across the boundary region. These boundaries are not ferroelectric but they can modulate the local electronic characteristics at the interface. The obtained results open a possibility to design and engineer electromechanical functionality in a wide variety of nominally nonpolar and non‐piezoelectric complex oxide heterostructures and thin films.     

Harnessing Selective Exsolution of Sn Metal to Enhance Electrical Conductivity in Oxygen-Deficient Perovskite Stannates

The versatile application of newly discovered oxide semiconductors calls for developing a simple process to generate conducting carriers. High-temperature reduction treatment leads to electrical conduction in perovskite stannate semiconductors, but carrier concentration is poorly controlled and inconsistently reported in BaSnO_3−δ films after the reduction process so far. Here, a new strategy to enhance the electrical conductivity of BaSnO_3−δ films is demonstrated by exploiting selective exsolution of Sn metals in the perovskite framework. Due to strong dependence of conductivity on initial Sn/Ba cation ratio in the reduced BaSnO_3−δ films, interestingly, only Sn-excess BaSnO_3−δ films show a dramatic increase of carrier concentration ( ∆ n_3D  = 5–7 × 10¹⁹ cm⁻³) after high-temperature reduction; exceptionally high electrical conductivity (σ  ≈  6000 S cm⁻¹) is achieved in reduced Sn-excess (La, Ba)SnO_3−δ films, which exceed full activation of La dopants in untreated (La, Ba)SnO₃. By multiple characterizations combined with theoretical calculation, it is disclosed that a small fraction of segregated β-Sn nanoparticles is likely to contribute the additional source of n_3D in the BaSnO_3−δ matrix as a result of spontaneous charge transfer from the segregated β-Sn metallic phase to BaSnO_3−δ. These original results propose a simple strategy to further increase electrical conductivity in perovskite oxide semiconductors by non-stoichiometry-driven metal exsolution.     

Sulfur stoichiometry driven chalcopyrite and pyrite structure of spray pyrolyzed Cu-alloyed FeS2 thin films

We report on fabrication of Cu_xFe_1−xS₂ (CFS) thin films using chemical spray pyrolysis followed by post-sulfurization. Post-sulfurized CFS films were grown with compact and good crystalline texture. The sulfur stoichiometry in CFS films was found to be crucial for determination of its crystal structure. The sulfur deficient CFS films were driven to chalcopyrite CFS (CH-CFS) structure whereas the sulfur cured CFS films were grown with Cu-incorporated pyrite CFS (P-CFS) structure which was confirmed by X-ray diffraction and Raman spectroscopy analysis along with UV–vis spectroscopy measurement. Electrical characterizations of both types of CFS films revealed p-type conductivity with carrier concentration in the range of 10¹⁸–10²⁰ cm⁻³ and mobility of 0.5–9 cm² V⁻¹ s⁻¹. The band gaps of CFS films of CH-CFS structure (0.885–0.949 eV) were found to be less than that of P-CFS structure (0.966–1.156 eV), which indicates its potential application for thermoelectric and photovoltaic devices.