Effect of annealing on structure and superconducting properties in Fe(Se,Te)

Abstract In this paper, the effect of post synthesis annealing treatments on a Fe(Se,Te) polycrystalline material is evaluated and discussed. The samples have been obtained via melting route. The material has been subjected to a high-temperature annealing treatment, carried out for 45 h at 680 °C. The role of the cooling step was investigated comparing samples obtained after a controlled cooling or after quenching in liquid nitrogen. From a morpho-structural point of view, the annealing treatment improves homogeneity, with respect to pristine samples, and influences secondary phase precipitate morphology. Regarding superconducting properties, a key role of the cooling procedure is assessed: controlled cooling leads in fact to a significant improvement of high field behaviour with respect to the melted material, while quenched samples are characterized by a worsening of the superconducting properties. Despite the overall worsening, however, the quenched samples show evidence of the presence of superconducting phases characterized by a remarkably high critical temperature (Tc > 18 K), observed for these materials only in films or under pressure

Effect of oxygen contamination on densification of Fe(Se,Te)

Abstract The optimization of sintering behaviour of iron chalcogenides superconducting materials is mandatory to enhance their critical current density, in order to pursuit their application in the production of superconducting wires. In this context it has been investigated here the effect of oxygen contamination on the material densification, considering the issues related to industrial oxygen-free isolated production lines. Our results show that the densification process is negatively affected by oxygen contamination. However, despite the difference in density, all sintered samples are characterized by similar structural and morphological features, and show comparable electrical and magnetic properties, with low critical current densities (Jc<103 A/cm2). These results suggest that densification is not the key limiting factor in these conditions, and that grain boundary or misorientation factors may play a greater role in limiting the performance of sintered iron chalcogenides superconductors

Hydrogen production by water splitting on manganese ferrite-sodium carbonate mixture. Feasibility tests in a packed bed solar reactor-receiver

The sodium manganese mixed ferrite thermochemical cycle Na(Mn1/3Fe2/3)O2/(MnFe2O4 + Na2CO3) for sustainable hydrogen production has been implemented in a solar reactor-receiver, packed with indirectly heated MnFe2O4/Na2CO3 mixture pellets, with the aim of verifying its feasibility and of determining the critical aspects of the process. The reactor operates at nearly constant temperature in the range 750–800 °C; the shift between the hydrogen-producing and regeneration steps is obtained by switching the reactive gas from water to carbon dioxide. Hydrogen produced during 1-h operation of the reactor is in the range of 130–460 μmol/g of mixture, depending on experimental conditions. Compared to other existing prototypes, the implemented process obtains comparable production efficiencies while operating at lower temperature both in the hydrogen production and regeneration phases

Phase Separation and Microstructure in Superconducting FeSe1-xTex Materials

In the effort to unveil the relations between synthesis conditions, morpho-structural features and superconducting properties of (11)-type iron-based superconductors, this study is focused on FeSe0.5Te0.5 materials obtained from high-temperature melts and different cooling rates. Crystalline and chemical composition are evaluated by means of XRD and SEM analyses, highlighting the formation of complex multiphase structures: the obtained results suggest that high-temperature nucleating phases may play a key role in the observed phase separation. Superconducting properties, evaluated by magnetization measurement and dc electrical resistance in different magnetic field conditions up to 18 T, highlight the low homogeneity of the superconducting phases, reflecting the microstructural observation

Hydrogen production by the sodium manganese ferrite thermochemical cycle-experimental rate and modeling

The sodium manganese ferrite thermochemical cycle for hydrogen production by water splitting can successfully operate in a relatively low temperature range (1023-1073 K) and has a high potential for coupling with the solar source using conventional structural materials. With the aim of implementing the cycle in a solar reactor, the hydrogen evolution rate from the reactive mixture measured in laboratory apparatus has been modeled by using a shrinking-core model. Such a model proved to adequately describe the rate of hydrogen production in the studied temperature and water concentration range. The model was extended to predict the behavior of the reactive mixture subjected to different experimental conditions. © 2014 American Chemical Society