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The superconductor $\mathrm{Mg}\mathrm{C}{\mathrm{Ni}}_{3}$ has been chemically doped by partial substitution of Ru for Ni in the solid solution $\mathrm{Mg}\mathrm{C}{\mathrm{Ni}}_{3\ensuremath{-}x}{\mathrm{Ru}}_{x}$ for $0lxl0.5$. Magnetic and specific heat measurements show that the Sommerfeld parameter $({\ensuremath{\gamma}}_{\mathrm{exp}})$ and ${T}_{C}$ decrease immediately on Ru substitution, but that a ${T}_{C}$ above $2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ is maintained even for a relatively large decrease in ${\ensuremath{\gamma}}_{\mathrm{exp}}$. Ferromagnetism is not observed to develop through Ru substitution, and the normal state magnetic susceptibility is suppressed.

The synthesis of three layer sodium cobalt oxide, NaxCoO2(x=0.3, 0.5, 0.6, 0.75 and 1.0) is reported. For x=0.6, 0.75, and 1.0, conventional solid-state synthesis was employed. x=0.3 and 0.5 were obtained via oxidative deintercalation of sodium at room temperature. x=0.3 can be hydrated to Na0.3CoO2•1.3H2O which is superconducting with a Tcof 4.3 K. Although having the same chemical stiochiometry as the previously reported two layer superconductor, it has a different stacking sequence of CoO2layers making it structurally distinct. Crystals of three layer NaCoO2show triangular morphology compared to hexagonal morphology for two layer Na0.7CoO2.

Although the microscopic origin of the superconductivity in high Tc copper oxides remains the subject of active inquiry, several of their electronic characteristics are well established as universal to all the known materials, forming the experimental foundation that all theories must address. The most fundamental of those characteristics is the dependence of the superconducting transition temperature on the degree of electronic band filling. Since the discovery of cuprate superconductivity in 1986 (1), the search for other families of superconductors that might help shed light on the superconducting mechanism of the cuprates has been of great interest. The recent report of superconductivity near 4K in the triangular lattice, layered sodium cobalt oxyhydrate, Na0.35CoO2.1.3H2O, is the best indication that superconductors related to the cuprates may be found (2). Here we show that the superconducting transition temperature of this compound displays the same kind of band-filling behavior that is observed in the cuprates. Specifically, that the optimal superconducting Tc occurs in a narrow range of band filling, and decreases for both underdoped and overdoped materials, in dramatic analogy to the phase diagram of the cuprate superconductors. Our results suggest that characterization of the detailed electronic and magnetic behavior of these new materials may help establish which of the many special characteristics of the cuprates is fundamental to their high Tc superconductivity., revised, publication information added

We report a corrected crystal structure for the CePt2In7 superconductor, refined from single crystal x-ray diffraction data. The corrected crystal structure shows a different Pt-In stacking along the c-direction in this layered material than was previously reported. In addition, all the atomic sites are fully occupied with no evidence of atom site mixing, resolving a discrepancy between the observed high resistivity ratio of the material and the atomic disorder present in the previous structural model The Ce-Pt distance and coordination is typical of that seen in all other reported Ce_nM_mIn_3n+2m compounds. Our band structure calculations based on the correct structure reveal three bands at the Fermi level that are more three dimensional than those previously proposed, and Density functional theory (DFT) calculations show that the new structure has a significantly lower energy., Comment: accepted by JPCM

Volumetric structures consisting of multilayer clads made of the bronze B10 and also of stellite SF6 alloys are prepared by laser remelting of the metal powder of the original particle size of ca 60 micrometers injected into the processing zone through a conical nozzle. For remelting with a cw CO 2 laser beam of intensities around 10 5 W/cm 2 and sample feed rates not exceeding 2.5 cm/s an efficient formation of the structures is observed and their geometry can be controlled. A fine grained, dendritic microstructure of the samples is observed by means of the optical and scanning microscopes. In the AFM scans the characteristic dimension of ca 60 nm reproduced in the periodic structures of the SF6 surface corresponds most probably to crystallines formed due to segregation after the liquid-solid phase transition. Similarly to SF6 the powderized B10 material is well suited for a fast prototyping.

An improvement of the reduction process through the presence of an extra copper pellet together with the Nd 2− x Ce x CuO 4 sample in an evacuated quartz tube is presented. Using this reduction technique, we have found that samples of Nd 1.85 Ce 0.15 Cu 1− y O 4− δ with copper deficiency y = 0.02 superconduct with T C = 23 K and the Meissner fraction is about 30%. X-ray diffraction (XRD) and energy dispersion X-ray analysis (EDAX) were used to characterize the surface of the samples. By means of DC magnetic measurement we have shown how deficiency and excess (2%) of copper in Nd 1.85 Ce 0.15 Cu 1± y O 4− δ influence the superconducting properties. At the end we compare the superconducting transition temperature of the samples treated in both the standard and modified reduction process.

The upper critical field (Hc2) in the doped and undoped intermetallic superconductor MgCNi3 is studied. In MgCNi3−xMx (M = Ru, Fe), Hc2 decreases monotonically as x increases. In the case of Fe doping, Hc2 changes most dramatically: from 10.7 T at x = 0 to 7.9 T at x = 0.015, which might be caused by the fact that the 3d electrons in Fe break superconducting Cooper-pairs. Although, doping carbon on the boron site in Mg(B1−xCx)2 has a substantial effect on the upper critical field, here we report that for MgC1−xBxNi3, boron substitution slightly increases Hc2 for the lowest B doping level, x = 0.04, only. For x > 0.04 the upper critical field decreases slowly as x increases. The initial slope of Hc2(T) in MgC0.96B0.04Ni3 is nearly the same as that of pure MgCNi3.

The (Bi,Pb)–Sr–Ca–Cu–O glass–ceramics may be considered as disordered metal and superconductor. Depending on the heat treatment conditions the materials are either composed of the oval grains of the 2212 or 2201 phases embedded in the insulating matrix or they mainly contain the 2212 plate-like crystallites weakly connected one with another. The materials have large resistivity and usually large negative temperature coefficient of resistivity (TCR). The granular and disordered character of the materials is also reflected in their superconducting properties. Both the normal-state and superconducting properties correlate one with another. The glass–ceramic samples were obtained by annealing the amorphous solid at temperatures between 840 and 860 °C. The measurements of the temperature dependence of resistivity in annealed samples were carried out with the conventional four-terminal method in a temperature range from 3 to 300 K.

We report the basic physical properties of monoclinic Y8Co5 determined by means of magnetic susceptibility, electrical resistivity, and specific heat measurements. The crystal structure of Y8Co5 is monoclinic (P2(1)/c) with lattice parameters a = 7.0582(6) Å, b = 7.2894(6) Å, c = 24.2234(19) Å, and β = 102.112(6)° as refined by using synchrotron powder x-ray diffraction data. The compound shows temperature independent paramagnetism with χ0 = 2.1 × 10(-3) emu mol(-1) and Sommerfeld parameter γ = 63 mJ mol(-1) K(-2). The calculated Wilson ratio for Y8Co5, R(W) = 1.4, is close to that expected for a free electron gas R(W) = 1. Low temperature resistivity under high pressure does not reveal superconductivity in this compound down to 1.2 K, up to hydrostatic pressures of 5.56 GPa. Band structure calculations (full-potential linearized augmented plane wave, FP-LAPW) derive the Stoner exchange interaction parameter S = 0.24, excluding magnetic behavior for Y8Co5.

The temperature dependencies of the in-plane ρ ab (T) and out-of-plane ρ c (T) resistivities of two groups of Nd 2 CuO 4 single crystals (films and bulk single crystals) was investigated in a temperature range 20-300 K. The effect of modified heated treatment and annealing conditions on transport properties of the pra-crystals Nd 2 CuO 4 was studied. It was found that nonstoichiometric disorder leads to different dependencies of the resistivity both ρ ab (T) and ρ c (T).

We report on the synthesis and physical characterization of a new compound, NpRh2Sn, prepared by arc-melting under argon atmosphere. Rietveld analysis of the powder x-ray diffraction pattern reveals an orthorhombic, Fe3C-type structure, with lattice parameters that are the shortest among the AnT2Sn series (An = U, Np, Pu, and T = Pd, Rh). A fit of the high-temperature magnetic susceptibility curve, χ(T), gives a Curie-Weiss temperature ΘCW = −29K, and an effective magnetic moment μeff = 2.42μB. The stabilization of the CW r eff r B antiferromagnetic order below TN = 34 K is revealed by a cusp in χ(T) and by a small anomaly in the specific heat curve, CP(T). An enhanced value of the Sommerfeld coefficient, γ ≈ 107 mJ mol−1 K−2, indicates a moderate heavy-fermion state. NpRh2Sn is the first member of the AnRh2Sn family, and a rare representative of heavy-fermion systems amidst Np- intermetallics.

Single crystals of YBa 2 Cu 3 O 7−δ have been grown from BaO - CuO flux. Surface studies of the oxidised crystals were done using optical polarizing microscope, scanning tunnelling (STM) and atomic force microscopy (AFM). Ferroelastic properties of YBa 2 Cu 3 O 7−δ crystals give a possibility to interpret twins within the framework of the quasidislocation theory. Analysis of this theoretical description gave an idea for investigating morphology of the twinned surface using STM and AFM microscopy. As the result for the first time it was possible to observe by AFM the twin boundaries as convexities of the twinned surface.

The influence of high-temperature reduction/oxidation treatment on the structural properties of superconducting PrBa 2 Cu 3 O 7−δ (PrBCO) single crystals was examined. The scanning electron microscopy (SEM) analysis has shown that even the short-lasting exposure to the oxygen-deficient atmosphere leads to creation of regular-shaped crystallites of PrBaO 3 and BaCuO 2 phases with the size of 0.5 ÷ 2.0 μ m on the smooth and flat crystal surface. The energy dispersive x-ray (EDX) investigations performed on the cross-sections of the superconducting crystals have indicated that the post-growth thermal treatment reduces the amount of Pr on the Ba-sites. Our results strongly support all the concepts attributing the suppression of superconductivity in this system to the excess of Pr in the crystal structure of samples synthesised by the standard methods.

A highly oxygen deficient perovskite, BaBi(0.28)Co(0.72)O(2.2), was synthesized by solid state reaction. The crystal structure was determined by means of neutron and x-ray powder diffraction. The material exhibits semiconducting behavior with an energy gap of 1.8 eV. The electron diffraction study does not reveal long range Bi:Co ordering; instead it shows the existence of short range ordering in this phase. The AC and DC magnetic susceptibility studies reveal cluster-glass behavior, which has its origin in the interacting ferromagnetic clusters present.

We report the synthesis and physical properties of single crystals of stoichiometric BaNi2As2 that crystalizes in the ThCr2Si2 structure with lattice parameters a = 4.112(4) \AA and c = 11.54(2) \AA. Resistivity and heat capacity show a first order phase transition at T_0 = 130 K with a thermal hysteresis of 7 K. The Hall coefficient is weakly temperature dependent from room temperature to 2 K where it has a value of -4x10^{-10} \Omega-cm/Oe. Resistivity, ac-susceptibility, and heat capacity find evidence for bulk superconductivity at T_c = 0.7 K. The Sommerfeld coefficient at T_c is 11.6 \pm 0.9 mJ/molK^2. The upper critical field is anisotropic with initial slopes of dH_{c2}^{c}/dT = -0.19 T/K and dH_{c2}^{ab}/dT = -0.40 T/K, as determined by resistivity., Comment: Published version: 4 pages, 4 figures

We report pressure-induced superconductivity in a single crystal of CaFe2As2. At atmospheric pressure, this material is antiferromagnetic below 170 K but under an applied pressure of 0.69 GPa becomes superconducting, with a transition temperature Tc exceeding 10 K. The rate of Tc suppression with applied magnetic field is −0.7 K T−1, giving an extrapolated zero-temperature upper critical field of 10–14 T.

The results of the tunneling microscopy and spectroscopy (STM/STS as well as atomic force microscopy (AFM) measurements on the Nd 2−x Ce x CuO 4−y (NCCO) single crystals in ambient conditions are presented with emphasis on material problems. The detailed spectroscopy and characteristic features of reduced NCCO single crystals in normal state are also discussed.

We report on the growth of PrBa 2 Cu 3 O 7-δ single crystals in the Al 2 O 3 and ZrO 2 crucibles by flux method. The high influence of the reaction between crucible and liquid on the initial melt composition has been established. We found that the precipitation of the chemically stable compound BaZrO 3 and BaAl 2 O 4 occurs by direct chemical reaction between BaCuO 2 and ZrO 2 or Al 2 O 3 crucibles materials. Free separated crystals with maximum size of 3 x 5 x 0.1 mm 3 have been obtained. PrBa 2 Cu 3 O 7-δ crystals exhibit a typically semiconducting behaviour. The resistivity depends on the thermal treatment and decreases by about two orders of magnitude for oxygen concentration between 6.65 to 6.95.