Structural studies and T c dependence in La2−x Dy x Ca y Ba2Cu4+y O z type mixed oxide superconductors

A new series of mixed oxide superconductors with the stoichiometric composition La_2−x Dy _x Ca _y Ba₂Cu_4+y O _z (x=0.0 − 0.5, y=2x) has been studied for structural and superconductiong properties. Our earlier studies on La_2−x (Y/Er) _x Ca _y Ba₂Cu_4+y O _z series, show a strong dependence of T _c on hole concentration (p _sh). In the present work, the results of the analysis of the neutron diffraction measurements at room temprerature on x=0.3 and 0.5 samples are reported. It is interesting to know that Ca substitutes for both La and Ba site with concomitant displacement of La onto Ba site. Superconductivity studies show that maximum T _c is obtained for x=0.5, y=1.0 sample (T _c ∼ 75 K), for La_1.5Dy_0.5Ca₁Ba₂Cu₅O _z (La-2125).     

Elastic properties of the Ta–V system: bcc Ta0.33V0.67 and C15 TaV2

Resonant ultrasound spectroscopy was used to measure the elastic constants of bcc Ta_0.33V_0.67 over the temperature range 3.5–300?K; the results were compared to earlier measurements on C15 TaV₂. The temperature dependence of the polycrystalline shear modulus is completely different in the two phases; that of the bcc phase decreases with temperature whereas that of the C15 phases increases in an anomalous fashion. This difference is consistent with a model involving doubly-degenerate levels at the X point of the Brillouin zone in the C15 phase with the Fermi level lying near the doubly degenerate level. This model accounted for the unusual behaviour of the C15 phase. Debye temperatures were determined from the ultrasonic measurements: 295?K for the C15 phase and 315?K for the bcc phase.     

Structural characteristics of different types of nanoparticles synthesised in mesomorphic metal alkanoates

The class of thermotropic ionic liquid crystals (LCs) of the metal alkanoates possesses a number of unique properties, such as intrinsic ionic conductivity, high dissolving ability and ability to form time-stable mesomorphic glasses. These ionic LCs can be used as nanoreactors for the synthesis and stabilisation of different types of nanoparticles (NPs). Thus, some semiconductors, metals and core/shell NPs were chemically synthesised in the thermotropic ionic liquid crystalline phase (smectic A) of the cadmium octanoate (CdC₈) and of the cobalt octanoate (CoC₈). By applying the scanning electron microscopy, the cadmium and cobalt octanoate composites containing CdS, Au, Ag and core/shell Au/CdS NPs have been studied. NPs’ sizes and dispersion distribution of the NPs’ size in the nanocomposites have been obtained.     

Unique activity of platinum adislands in the CO electrooxidation reaction

The development of electrocatalytic materials of enhanced activity and efficiency through careful manipulation, at the atomic scale, of the catalyst surface structure has long been a goal of electrochemists. To accomplish this ambitious objective, it would be necessary both to obtain a thorough understanding of the relationship between the atomic-level surface structure and the catalytic properties and to develop techniques to synthesize and stabilize desired active sites. In this contribution, we present a combined experimental and theoretical study in which we demonstrate how this approach can be used to develop novel, platinum-based electrocatalysts for the CO electrooxidation reaction in CO(g)-saturated solution; the catalysts show activities superior to any pure-metal catalysts previously known. We use a broad spectrum of electrochemical surface science techniques to synthesize and rigorously characterize the catalysts, which are composed of adisland-covered platinum surfaces, and we show that highly undercoordinated atoms on the adislands themselves are responsible for the remarkable activity of these materials.     

Using Surface Segregation To Design Stable Ru‐Ir Oxides for the Oxygen Evolution Reaction in Acidic Environments

The methods used to improve catalytic activity are well‐established, however elucidating the factors that simultaneously control activity and stability is still lacking, especially for oxygen evolution reaction (OER) catalysts. Here, by studying fundamental links between the activity and stability of well‐characterized monometallic and bimetallic oxides, we found that there is generally an inverse relationship between activity and stability. To overcome this limitation, we developed a new synthesis strategy that is based on tuning the near‐surface composition of Ru and Ir elements by surface segregation, thereby resulting in the formation of a nanosegregated domain that balances the stability and activity of surface atoms. We demonstrate that a Ru_0.5Ir_0.5 alloy synthesized by using this method exhibits four‐times higher stability than the best Ru‐Ir oxygen evolution reaction materials, while still preserving the same activity.