The structural features of the antiferromagnetic K0.8Fe1.6S2 have been studied in the temperature range from 300 K up to 700 K by means of in situ transmission electron microscopy (TEM). The superstructure with a wave vector originating from a Fe-vacancy order has been clearly observed; moreover, the structural analysis shows that K0.8Fe1.6S2 undergoes a transition from the Fe-vacancy order to disorder at about 585 K. The S substitution effect on the phase separation and superconductivity in the K0.8Fe1.75Se2−ySy materials has been systematically investigated by SEM and TEM structural analyses, as well as by electrical resistivity measurements. Our experimental results reveal that the S element adopts a homogeneous distribution in all investigated materials, and the essential phase-separation nature is very similar to what was observed in the K0.8Fe1.75Se2 superconductor. A phase-separated state formed by the coexistence of two Fe-vacancy orders with wave vectors and in K0.8Fe1.5+xS2 (0 < x < 0.1) has been briefly discussed.

A variety of techniques for the measurement of emissivity is available today but in many cases these techniques do not adequately meet the wide range of requirements posed by modern science and industry. Furthermore, they do not provide sufficiently accurate results and lack reliable and traceable uncertainties. Therefore, a measurement setup and a validated method for highly accurate directional spectral emissivity, total directional emissivity and total hemispherical emissivity measurements under vacuum in the wavelength range from 4 µm to 100 µm and a temperature range from-40 °C to 600 °C with validated uncertainties was developed at the Physikalisch-Technische Bundesanstalt (PTB). Using a direct radiometric method with two reference blackbodies, the measurements at this facility, the Reduced Background Calibration Facility (RBCF), are traceable to the International Temperature Scale of 1990 (ITS-90).