Xian Zhang

The possibility of superconductivity in tetragonal FeS has attracted considerable interest because of its similarities to the FeSe superconductor. However, all efforts made to pursue superconductivity in tetragonal FeS have failed so far, and it remains controversial whether tetragonal FeS is metallic or semiconducting. Here we report the observation of superconductivity at 5 K in tetragonal FeS that is synthesized by the hydrothermal reaction of iron powder with sulfide solution. The obtained samples are highly crystalline and less air-sensitive, in contrast to those reported in the literature, which are meta-stable and air-sensitive. Magnetic and electrical properties measurements show that the samples behave as a paramagnetic metal in the normal state and exhibit superconductivity below 5 K. The high crystallinity and the stoichiometry of the samples play important roles in the observation of superconductivity. The present results demonstrate that tetragonal FeS is a promising new platform to realize high-temperature superconductors.

With the addition of oxygen into the chain-like bismuth sulfide of Bi2S3, there are two interesting functional compounds of Bi2O2S (photoelectric) and Bi4O4S3 (superconducting) containing the PbO-like [Bi2O2] layers. Nanoscale Bi2O2S crystals with an indirect band gap of 1.12 eV are synthesized via a facile hydrothermal method. This semiconductor shows excellent photoelectric response under the irradiation of visible light lamp at room temperature. Theoretical calculations and packing factor model both indicate that the loosely packed Bi2O2S is an excellent photoelectric material. When the Bi2O2S phase was annealed at 500 °C in an evacuated quartz tube, nanocrystals of Bi4O4S3 were obtained. The powder X-ray diffraction and electron microscope analyses (SEM, TEM, EDX) confirmed the thermal decomposition from orthorhombic Bi2O2S to tetragonal Bi4O4S3. The superconducting transition temperature of Bi4O4S3 was observed to be 4.6 K from the temperature-dependence measurements of electrical resistivity and magnetic susceptibility. Our results also provide a new method utilizing thermal decomposition to prepare a new phase without high temperature reaction.

Galfan coatings on steel in laboratory exposures with predeposited NaCl and cyclic wet/dry conditions exhibit nearly the same corrosion products as after 5 years of marine exposure. A general scenario for corrosion product evolution on Galfan in chloride-rich atmospheres is proposed. It includes the initial formation of ZnO, ZnAl2O4 and Al2O3 and subsequent formation of Zn6Al2(OH)16CO3⋅4H2O, and Zn2Al(OH)6Cl⋅2H2O and/or Zn5Cl2(OH)8⋅H2O. An important phase is Zn6Al2(OH)16CO3⋅4H2O, which largely governs the reduced long-term zinc runoff from Galfan. A clear influence of microstructure could be observed on corrosion initiation in the slightly zinc-richer η-Zn phase adjacent to the β-Al phase.