Resistivity, magnetic susceptibility and heat capacity measurements are reported for single crystals of Fe 1+y Te x Se 1-x grown via a modified Bridgeman method with 0 < y < 0.15, and x= 1, 0.9, 0.75, 0. 67, 0.55 and 0.5. Although resistivity measurements show traces of superconductivity near 14 K for all x except x=1, only crystals grown with compositions near x=0.5 exhibit bulk superconductivity. The appearance of bulk superconductivity correlates with a reduction in the magnitude of the magnetic susceptibility at room temperature and smaller values of y, the concentration of Fe in the Fe(2) site.
Composition, crystal structure, and stability of the thermoelectric material, known in the literature as "Zn 4 Sb 3 ", has been characterized using low-and room-temperature single-crystal X-ray diffraction techniques, as well as in situ room-and high-temperature powder X-ray diffraction methods. We have found that the Zn 4 Sb 3 phase does not exist below 767 K (the β−γ transition temperature); it is the Zn 6-δ Sb 5 phase that is erroneously assigned the Zn 4 Sb 3 composition and is considered to be a promising thermoelectric material. The structure of Zn 6-δ Sb 5 is similar to that of "Zn 4 Sb 3 " but no Zn/Sb mixture is observed on any Sb site. Instead, a significant deficiency on the Zn site is discovered. There are two, not one, as previously reported, Zn 6-δ Sb 5 polymorphs below room temperature. In dynamic vacuum and at elevated temperatures the Zn 6-δ Sb 5 phase becomes zinc poorer due to zinc sublimation and eventually decomposes into ZnSb and Zn before reaching its melting temperature of 841 K. The binary Zn 1-δ Sb compound also loses zinc in dynamic vacuum and at high temperatures and decomposes into Sb and Zn. The structure of Zn 1-δ Sb (CdSb-type) is analyzed using powder X-ray diffraction techniques. Disciplines
We investigate the physical properties and electronic structure upon Cr-doping in the iron arsenide layers of BaFe 2 As 2 . This form of hole-doping leads to suppression of the magnetic/structural phase transition in BaFe 2-x Cr x As 2 for x > 0, but does not lead to superconductivity. For various x values, temperature dependence of the resistivity, specific heat, magnetic susceptibility, Hall coefficient, and single crystal x-ray diffraction data are presented. The materials show signatures of approaching a ferromagnetic state with x, including a metamagnetic transition for x as little as 0.36, an enhanced magnetic susceptibility, and a large Sommerfeld coefficient. Such results reflect renormalization due to spin fluctuations and they are supported by density functional calculations at x = 1.Calculations show a strong interplay between magnetic ordering and chemical ordering of Fe and Cr, with a ferromagnetic ground state. This ferromagnetic ground state is explained in terms of the electronic structure. The resulting phase diagram is suggestive that superconductivity does not derive simply from the suppression of the structural/magnetic transitions.2
The crystal structure, electrical resistivity, magnetic susceptibility, and heat capacity of single crystals of BaFe 2 As 2 , BaNi 2 As 2 , and BaFeNiAs 2 are reported. BaFe 2 As 2 data indicate the equivalence of C͑T͒, d͑T͒ / dT, and d / dT results in determining the antiferromagnetic transition at T N = 132͑1͒K. BaNi 2 As 2 shows a structural phase transition from a high-temperature tetragonal phase to a low-temperature triclinic phase ͑P1 symmetry͒ at T 0 = 131 K, with superconducting critical temperature T c = 0.69 K. BaFeNiAs 2 does not show any sign of superconductivity and its properties resemble BaCo 2 As 2 , a renormalized paramagnetic metal.
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