Crystals of FeSe0.88 and FeSeMn0.1 have been grown from KCl solutions. Crystals measuring 2−3 mm across and 0.1−0.3 mm thick grow with a hexagonal plate like habit. Powder X-ray diffraction (XRD) measurements show strong peaks corresponding to the tetragonal α-FeSe phase and weak hexagonal β-FeSe peaks in both cases. The plate side of the crystal is identified to be the (101) face of the tetragonal α-FeSe. Energy dispersive X-ray spectroscopic (EDS) measurements show that Mn substitutes for Fe. Both types of crystals show a superconducting transition at 8 K in the DC magnetization measurements and a broad resistive transition with zero resistance at 7.5 K with an onset at 11 K. Specific heat measurements also confirm bulk superconductivity in the crystals. Crystals could also be grown using KBr as a solvent.
A new approach to grow FeSe 1-x Te x single crystals with optical zone-melting technique was successfully employed. Crystals with actual composition 0.4 ≤ x ≤ 1.0 all show high crystallinity with no phase separation. The ability to visually observe the locally heated melt, and ease of use and control of the image furnace make this method a promising and time-efficient way for obtaining highquality FeSe 1-x Te x crystals. Our results indicate that with adequate heat treatment, the non-uniform distribution of Se and Te atoms in crystal lattice can be effectively eliminated, while the transition width of superconductivity can be reduced to about 2 K, which suggest the crystals are homogeneous in nature.
Nanotubular TiO2 has attracted considerable attention owing to its unique functional properties, including high surface area and vectorial charge transport along the nanotube, making it a good photocatalytic material. Anodic TiO2-nanotube (TiNT) arrays on a Ti foil substrate were prepared by electrochemical anodic oxidation and SEM/HRTEM/XRD analyses have suggested that the walls of TiO2 tubes are formed from stacked [101] planes (anatase). Both HRTEM and XRD indicate an interplanar spacing of d101 = 0.36 nm in the wall structure. Despite the large amount of work done on nanotube synthesis, a thorough investigation of the electronic and atomic structures of free-standing TiNT arrays has not yet been carried out. X-ray absorption spectroscopy (XAS), resonant inelastic X-ray scattering (RIXS) and scanning photoelectron microscopy (SPEM) are employed herein to examine the electronic and atomic structures at the top and bottom of TiNT arrays. These analyses demonstrate the presence of mixed valence states of the Ti ions (Ti(3+) and Ti(4+)) and a structural distortion at the bottom cap region of the TiNT. Additionally, the results obtained herein suggest the formation of a defective anatase phase at the bottom cap barrier layer between the Ti foil substrate and TiNT during the growth of electrochemically anodized nanotubes.
We utilize steady-state and transient optical spectroscopies to examine the responses of nonthermal quasiparticles with respect to orbital modifications in normal-state iron-chalcogenide superconductors. The dynamics shows the emergence of gaplike quasiparticles (associated with a ~36 meV energy gap) with a coincident transfer of the optical spectral weight in the visible range, at temperatures above the structural distortion. Our observations suggest that opening of the high-temperature gap and the lattice symmetry breaking are possibly driven by short-range orbital and/or charge orders, implicating a close correlation between electronic nematicity and precursor order in iron-based superconductors.
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