ZnTe nanowires were grown by molecular beam epitaxy on GaAs substrates of three different orientations: (100), (110), and (111)B. The catalyst droplets were produced through in situ annealing of a previously deposited Au layer and by forming the eutectic alloy with Ga from the substrate. The influence of substrate orientation and growth parameters on the properties of nanowires was investigated using scanning and transmission electron microscopy, energy dispersive x-ray spectroscopy, and x-ray diffraction. The growth process was based on the vapour–liquid–solid mechanism and the contribution of the diffusion-induced effect in this mechanism was confirmed by correlating the length and the diameter of the produced nanowires. The nanowires had diameters ranging from 30 to 70 nm and lengths between 1 and 2 µm. The growth axis of the nanowires was and the nanowires grew along directions of the substrate, independent of the substrate orientation used. The nanowires had stacking faults at the bottom and those grown at optimal conditions possessed perfect cubic structure near the top.

In this paper, we address a number of outstanding issues concerning the nature and the role of magnetic inhomogenities in the iron chalcogenide system FeTe 1-x Se x and their correlation with superconductivity in this system. We report morphology of superconducting single crystals of FeTe 0.65 Se 0.35 studied with transmission electron microscopy, high angle annular dark field scanning transmission electron microscopy and their magnetic and superconducting properties characterized with magnetization, specific heat and magnetic resonance spectroscopy. Our data demonstrate a presence of nanometre scale hexagonal regions coexisting with tetragonal host lattice, a chemical disorder demonstrating non homogeneous distribution of host atoms in the crystal lattice, as well as hundreds-of-nanometres-long iron-deficient bands. From magnetic data and ferromagnetic resonance temperature dependence, we attribute magnetic phases in Fe-Te-Se to Fe 3 O 4 inclusions and to hexagonal symmetry nanometre scale regions with structure of Fe 7 Se 8 type. Our results suggest that nonhomogeneous distribution of host atoms might be an intrinsic feature of superconducting Fe-Te-Se chalcogenides and we find a surprising correlation indicating that faster grown crystal of inferior crystallographic properties is a better superconductor.

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CaMnO 3 is a parent compound for numerous multicomponent manganese perovskite oxides. Its crystallographic data are of primary importance in the science and technology of functional CaMnO 3 -based materials. In the present study, data were collected for a CaMnO 3 sample at 302 K. The crystal structure refinement yields accurate absolute values of lattice parameters, a = 5.281 59͑4͒ Å, b = 7.457 30͑4͒ Å, and c = 5.267 48͑4͒ Å, leading to orthorhombic distortion of ͑c / a , ͱ 2c / b͒ = ͑0.997 33, 0.998 95͒. The orthorhombic distortion of the CaMnO 3 structure is discussed on the basis of comparison of our unit-cell size with data already published. At a graphical representation of the distortion, it is observed that there is a considerable scatter of the distortion values among the literature data but, interestingly, a considerable fraction of experimental results ͑including the present one͒ for stoichiometric samples are grouped around the distortion ͑c / a , ͱ 2c / b͒ = ͑0.9973, 0.9990͒, which lies close to a maximum in the extent of orthorhombicity. The influence of off-stoichiometry on the orthorhombic distortion is discussed on the basis of available experimental data. Simulations, employing a mean-field approach for low temperatures, predict an increase in cell volume and structural distortions with the concentration of oxygen vacancies when the additional electrons are localized on the manganese. A simple model of delocalization produced the opposite effect, which is expected to combine with lattice vibrations to recover the cubic phase at high temperatures.