- Angular dependence of pinning potential, upper critical field, and irreversibility field in underdoped BaFe1.9Co0.1As 2 single crystal
-
Underdoped BaFe1.9Co0.1As2 single crystal was studied by angular dependence of magneto-transport at fields up to 13 T over a wide range of temperature. Our results show that pinning potential, U o, decreases slightly for 45 and remains constant for 45, while the upper critical field, Hc2, and the irreversibility field, H irr, increase with . According to anisotropic Ginzburg-Landau theory, the anisotropy was determined by scaling the resistivity under different magnetic fields below the superconducting critical temperature, Tc. Anisotropy, , in the underdoped crystal is found to be temperature dependent and decreases from 2.1 to 1.8 for as T is reduced from 17 to 12.5 K.
- Shahbazi,Wang,Ghorbani,Dou,Choi
-
-
Read Online
- Studies on effects of impurity doping and NMR measurements of La 1111 and/or Nd 1111 Fe-Pnictide superconductors
-
Measurements of the electrical resistivity ρ, Hall coefficient R H, thermoelectric power S, and the electronic specific heat coefficient γ have been carried out for samples of LnFe 1-yMyAsO1-xFx (Ln = La, Nd; M = Co, Mn; x = 0:11) obtained by doping M atoms into the superconducting LnFeAsO 1-xFx (Ln 1111) system. The NMR longitudinal relaxation rate 1/T1 has also been measured for samples of LnFe 1-yMyAsO1-xFx with various x values. Co atoms doped into the superconducting LnFeAsO1-xFx are nonmagnetic, and the rate of Tc-suppression |dTc/dx| by Co atoms has been found to be too small to be explained by the pair-breaking effect expected for the S± superconducting symmetry proposed as the most probable symmetry for the system. This result throws a serious doubt on whether the symmetry is realized in the system. Instead of the pair breaking, two mechanisms of Tc suppression by the doped impurities have been found: One is the electron localization, which appears when the sheet resistance R□ exceeds h/4e2 = 6:45 kΩ, and the other is the disappearance (or reduction in the area) of the hole Fermi surfaces around the Γ point in the reciprocal space. The latter mechanism has been observed when the number of electrons increases with increasing Co doping level and the system changes from an anomalous metal to an ordinary one. Regarding the two distinct T dependences of the NMR longitudinal relaxation rate 1/T 1 of LaFeAsO1-xFx, (1=T1 ∝ T6 reported by our group in the T region from Tc to ~0:4 Tc for samples with the highest Tc values with varying x, and 1/T1 ∝ T2:5-3:0 observed by many groups in almost the entire T region studied below Tc), we discuss the origin of such a difference, and show that, at least, the T2:5-3:0-like dependence of 1/T1 cannot be considered as the experimental evidence for the S± symmetry of δ.
- Sato, Masatoshi,Kobayashi, Yoshiaki,Lee, Sang Chul,Takahashi, Hidefumi,Satomi, Erika,Miura, Yoko
-
-
Read Online
- A new chemical route to prepare nanocrystalline cobalt monoarsenide
-
A low-temperature solvothermal reduction process to nanocrystalline CoAs is reported here. All the precursors are easily accessible. The formation and crystalline temperature of CoAs could be as low as 140°C. Powder X-ray diffraction (XRD) shows a single phase of CoAs. The average particle size observed from transmission electron micrography (TEM) is about 18 nm. Elemental analysis and X-ray photoelectron spectroscopy (XPS) were utilized to determine the chemical composition of the product.
- Wang,Qian,Zhang,Li,Xie,Qian
-
-
Read Online
- Magnetic and transport properties of SmCoAsO1-xFx
-
A series of SmCoAsO1-xFx (with x=0, 0.05, 0.1, and 0.2) samples have been prepared by solid state reactions. X-ray powder diffraction proved that all samples can be indexed as a tetragonal ZrCuSiAs-type structure. A clear shrinkage of the lattice constants a and c with increasing F content indicated that F has been doped into the lattice. The magnetic and transport properties of the samples have been investigated. Parent SmCoAsO compound exhibited complicated magnetism including antiferromagnetism, ferromagnetism, and ferrimagnetism. For the fluorine doped samples, the antiferromagnetic Néel temperatures were almost independent of the F content and metamagnetic transitions were observed below antiferromagnetic Néel temperatures. With increasing F content, high temperature (below 142 K) ferrimagnetic state gradually changed to ferromagnetic state. In the resistivity result, metallic conduction in the region of 2300 K and Fermi liquid behavior at low temperatures were shown in all samples. Transport properties at applied magnetic fields showed anomalies at low temperatures.
- Chen,Cui,Yang,Cheng,Zhao
-
-
Read Online
- Cobalt-metalloid alloys for electrochemical oxidation of 5-hydroxymethylfurfural as an alternative anode reaction in lieu of oxygen evolution during water splitting
-
The electrochemical water splitting commonly involves the cathodic hydrogen and anodic oxygen evolution reactions (OER). The oxygen evolution reaction is more energetically demanding and kinetically sluggish and represents the bottleneck for a commercial competitiveness of electrochemical hydrogen production from water. Moreover, oxygen is essentially a waste product of low commercial value since the primary interest is to convert electrical energy into hydrogen as a storable energy carrier. We report on the anodic oxidation of 5-hydroxymethylfurfural (HMF) to afford the more valuable product 2,5-furandicarboxylic acid (FDCA) as a suitable alternative to the oxygen evolution reaction. Notably, HMF oxidation is thermodynamically more favorable than water oxidation and hence leads to an overall improved energy efficiency for H2 production. In addition, contrary to the “waste product O2”, FDCA can be further utilized, e.g., for production of polyethylene 2,5-furandicarboxylate (PEF), a sustainable polymer analog to polyethylene terephthalate (PET) and thus represents a valuable product for the chemical industry with potential large scale use. Various cobalt-metalloid alloys (CoX; X = B, Si, P, Te, As) were investigated as potential catalysts for HMF oxidation. In this series, CoB required 180 mV less overpotential to reach a current density of 55 mA cm?2 relative to OER with the same electrode. Electrolysis of HMF using a CoB modified nickel foam electrode at 1.45 V vs RHE achieved close to 100% selective conversion of HMF to FDCA at 100% faradaic efficiency.
- Weidner, Jonas,Barwe, Stefan,Sliozberg, Kirill,Piontek, Stefan,Masa, Justus,Apfel, Ulf-Peter,Schuhmann, Wolfgang
-
p. 1436 - 1445
(2018/07/05)
-
- Doping dependence of magnetic and transport properties in single crystalline Co-doped BaFe2As2
-
We report the doping dependence of transport and magnetic properties in Co-doped BaFe2As2. With increasing Co concentration x, structural and magnetic transitions are suppressed and superconductivity emerges in the range of 0.3c at low temperatures and low fields obtained from bulk magnetization is reasonably large and the doping dependence shows a maximum at x~0.07 similar to Tc. The values of Jc at low temperatures reach about 1×106A/cm2 around the optimally doped region, which is potentially attractive for technological applications.
- Nakajima, Yasuyuki,Taen, Toshihiro,Tamegai, Tsuyoshi
-
p. S408-S410
(2011/02/28)
-
- Possible superconductivity above 25K in single-crystalline Co-doped BaFe2As2
-
We present the superconducting properties of single-crystalline Ba(Fe 0:9Co0:1)2As2 by measuring its magnetization, resistivity, upper critical field, Hall coefficient, and magneto-optical images. The magnetizat
- Nakajima, Yasuyuki,Taen, Toshihiro,Tamegai, Tsuyoshi
-
-
- Next-nearest neighbour contributions to the XPS binding energies and XANES absorption energies of P and As in transition-metal arsenide phosphides MAs 1-yPy having the MnP-type structure
-
X-ray photoeleetron spectroscopic (XPS) and X-ray absorption near-edge spectroscopic (XANES) measurements have been made for several series of metal arsenide phosphides MAs1-yPy, (M= Co, Fe, Cr) that adopt the MnP-type structure. The P and As XPS binding energies (BEs) and XANES absorption energies of the metal arsenide phosphides do not follow the trend observed for the simple binary phosphides or arsenides, a deviation that arises from the combination of nearest and nextnearest neighbour contributions acting on the P or As photoemission or absorption site. The P 2p3/2 BEs and K-edge absorption energies are lower in MAs1-yPy than in MP because the P atoms are more negatively charged and because the P photoemission or absorption site is screened to a greater extent by less positively charged nearest-neighbour M atoms and more negatively charged next-nearest neighbour P atoms. The As L3- and K-edge absorption energies are higher in MAs1-yPy than in MAs primarily because the As atoms are less negatively charged. The M charge has been evaluated from analysis of the M 2p XPS spectra and the M L- and K-edge XANES spectra.
- Grosvenor, Andrew P.,Cavell, Ronald G.,Mar, Arthur
-
p. 2549 - 2558
(2009/02/06)
-
- Liquid ammonia mediated metathesis: Synthesis of binary metal chalcogenides and pnictides
-
Addition of stoichiometric amounts of low valent metal halides to liquid ammonia solutions of disodium chalcogenide (Na2E; E = S, Se, Te) afforded a range of both crystalline (PbE (E = S, Se, Te), TIE (E = S, Se), Tl5Te3, Ag2E (E = S, Se, Te)) and X-ray amorphous (MS (M = Ni, Cu, Zn, Cd, Hg), M2E3 (M = Ga, In; E = S, Se, Te), HgE (E = Se, Te), CuE (E = S, Se, Te), Cu2S) metal chalcogenides in good yield (95%). Reactions between metal halides and sodium pnictides (Na3Pn; Pn = As, Sb) in liquid ammonia also afforded X-ray amorphous material (M3Pn2, M = Zn, Cd; MPn, M = Fe, Co, Ni) in good yield (95%). Isolation of the metal chalcogenides and pnictides was achieved through washing with CS2 and distilled water. All reactions were complete within 36 h. Products were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDXA), electron probe analysis, FR-IR spectroscopy, Raman spectroscopy, microanalysis, and band gap measurements. Annealing amorphous material at 250-300 °C for 48 h induced sufficient crystallinity for analysis by X-ray powder diffraction.
- Shaw,Parkin
-
p. 6940 - 6947
(2008/10/08)
-
- A safe low temperature route to nanocrystalline transition metal arsenides
-
Nanocrystalline FeAs, CoAs and NiAs were prepared by keeping the mixture of FeCl3, CoCl2 or NiCl2 with arsenic and KBH4 in ethylenediamine (en) at 100 °C for 4 h, respectively. X-Ray powder diffraction (XRD) patterns and transmission electron microscope (TEM) images show that the products are orthorhombic FeAs, CoAs and hexagonal NiAs, respectively, and all are well crystalline in nanometers.
- Xie, Yi,Lu, Jun,Yan, Ping,Jiang, Xuchuan,Qian, Yitai
-
p. 114 - 115
(2007/10/03)
-
- Liquid-mediated metathetical synthesis of binary and ternary transition-metal pnictides
-
Nickel and cobalt pnictides have been synthesised using a liquid-mediated metathetical reaction of transition-metal dihalides with the appropriate sodium pnictide Na3E (E = P, As, Sb) in refluxing toluene for 48 h. Binary and ternary compounds have been prepared. Products were analysed by powder X-ray diffraction, scanning electron microscopy, energy dispersive analysis by X-rays, FT-IR, Raman and vibrating sample magnetometry. (C) 2000 Elsevier Science Ltd.
- Carmalt, Claire J.,Morrison, Daniel E.,Parkin, Ivan P.
-
p. 829 - 833
(2008/10/08)
-