A. Hackemer

Search for unconventional superconductors among the YTE2Si2compounds (TE = Cr, Co, Ni, Rh, Pd, Pt)

Motivated by the recent discovery of exotic superconductivity in YFe2Ge2 we undertook reinvestigation of formation and physical properties of yttrium-based 1:2:2 silicides. Here we report on syntheses and crystal structures of the YTE 2Si2 compounds with TE  =  Cr, Co, Ni, Rh, Pd and Pt, and their low-temperature physical properties measurements, supplemented by results of fully relativistic full-potential local-orbital minimum basis band structure calculations. We confirm that most of the members of that family crystallize in a tetragonal ThCr2Si2-type structure (space group I4/mmm) and have three-dimensional Fermi surface, while only one of them (YPt2Si2) forms with a closely-related primitive CaBe2Ge2-type unit cell (space group P4/nmm) and possess quasi-two-dimensional Fermi surface sheets. Physical measurements indicated that BCS-like superconductivity is observed only in YPt2Si2 (T c  =  1.54 K) and YPd2Si2 (T c  =  0.43 K), while no superconducting phase transition was found in other systems at least down to 0.35 K. Thermal analysis showed no polymorphism in both superconducting phases. No clear relation between the superconductivity and the crystal structure (and dimensionality of the Fermi surface) was observed.

Hydrogenation and Corrosion Properties of LaNi4.5Co0.5-Based Alloy Doped with 1.7 at% Sn

Effect of small addition of tin (1.7 at.%) into LaNi4.5Co0.5 alloy on gas phase and cathodically charged hydrogen absorption ability as well as its corrosion resistance in 6M KOH solution is discussed. To reveal the effect of Sn doping three alloys have been selected: LaNi4.5Co0.5 (precursor), LaNi4.5Co0.5Sn0.1 and LaNi5 - as a parent compound. The room temperature p-C isotherms indicate to beneficial effect of Sn addition which causes decrease of H2 equilibrium pressure and does not limit atomic hydrogen solubility. Discharge capacities (Qdisch), exchange current densities of H2O/H2 system () as well as corrosion rates () have been determined for the tested alloys on the basis of cyclic galvanostatic measurements (at –0.5C/+0.5C rates). It has been shown that for N > 3 cycle the discharge capacity of LaNi4.5Co0.5 is ca twofold greater than that for LaNi5 reference. Addition of 1.7 at.% Sn into Co-containing alloy expands the discharge capacity by 30-40%. The Co containing alloys reveal twice as great exchange current densities of H2O/H2 system compared to LaNi5, however, Sn addition slightly decreases the , especially for latest cycles. The partial cobalt substitution for Ni accelerates alloy corrosion in alkaline solution, however, tin addition fully eliminates this effect.

Hydrogen sorption and corrosion properties of La2Ni9CoSn0.2 alloy

Abstract The hydrogenation and corrosion behaviour of La2Ni9 · CoSn0.2 alloy was analysed in respect of its use in Ni–MH batteries. It has been proved that the presence of tin in the alloy causes a decrease in hydrogen equilibrium pressure. In the electrochemical studies several techniques, such as chronopotentiometry, multi-potential steps, linear sweep voltammetry and the potentiokinetic polarization were applied to characterize the electrochemical properties of a La2Ni9CoSn0.2 powder composite electrode. During long cycling, powder particles undergo micro-cracking or other forms of surface development causing a progressive increase in the exchange current density of the H2O/H2 system, but, on the other hand, this increase favours corrosion processes such as the electrode materials oxidation. This is also reflected in the capacity loss values.