Search

Polycrystalline samples of Sr2VFeAsO3-δ with perovskite-type carrier blocking layers were prepared by a solid state reaction using an alumina tube in a sealed silica tube. Sr2VFeAsO3-δ samples which were prepared as nominally δ = 0 were not synthesized as a single phase, suggesting that finite oxygen deficiency is inevitable for the compound. Although a sample, which exhibits relatively larger lattice volume, does not exhibit bulk superconductivity at temperatures ≥5 K, finite superconducting transition temperatures appear in the sample which exhibits smaller lattice volumes. These results support making the electronic and magnetic phase diagram of Sr2VFeAsO3-δ. [ABSTRACT FROM AUTHOR]

We have studied pressure effects on the magnetic and electronic nature of layered oxysulfide Sr2Cu2CoO2S2 which crystallizes in an unusual intergrowth structure. The derivative permeability (dμ/dT) curves have a kink near Tt at which the antiferromagnetic nature is changed from 2D to 3D; Tt extremely rises with increasing pressure (dTt/dP=13.5 K/kbar), indicating that 3D antiferromagnetic state is more stable under pressure. The Tt in the dμ/dT curves correspond to the bending point of the resistivity, and above Tt the nearest-neighbor hopping conduction occurs. These features would be discussed from the viewpoint of the coupled nature of charge carriers and 2D antiferromagnetic spin ordering. [Copyright &y& Elsevier]

We have studied the magnetic dilution and electronic nature of Zn doping on the Mn site in the colossal magnetoresistant material La0.7Pb0.3MnO3 (x≤0.3). Small non-magnetic Zn2+ doping tends to separate the system into ferromagnetic clusters to weaken the long-range ferromagnetic order and to reduce the Curie temperature. The spin polarizability of the x=0–0.3 samples is estimated to be 0.97–1.00, indicating that the x=0–0.3 samples are the spin polarized materials in which the conductivity is dominated by single-spin charge carriers. Small doping (x≥0.1) induces the metal–insulator transition and destroys the metallic state with long-range ferromagnetic order. [Copyright &y& Elsevier]

Electronic structures of orthorhombic and monoclinic Cu4SnS4, which exhibit a first-order phase transition at 232 K, are demonstrated based on the generalized gradient approximation (GGA) of the density functional theory (DFT). The calculated band gap was 0.39 eV for orthorhombic phase, while that was not obtained for monoclinic one. These calculated results confirm monoclinic phase has smaller activation energy ( Ea) than orthorhombic phase. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Abstract: has a spin-glass phase below 60K ( ) and a ferrimagnetic phase in the temperature range 60–170K ( 170K). Mn doping gives an increase of a paramagnetic phase which coexists with a ferrimagnetic phases, and shift of magnetic transition temperature ( 45K, 130K for ). The conduction property changes into variable range hopping (VRH) from thermal activated transport below for . This conducting transition would be associated with the correlated Fe 3d orbital ordering below . [Copyright &y& Elsevier]

We investigated the magnetic properties of polycrystalline Co3Sn2S2- xSe x (0≤ x ≤1.2) to ascertain the magnetism of the metallic ferromagnet Co3Sn2S2. In Co3Sn2S2- xSe x, TC and magnetization gradually decrease with increasing x, but there is no magnetic phase transition from ferromagnetic throughout the full range of composition. These results indicate that Se substitution effect on magnetism is small compared with In and Ni substitution. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The thermoelectric properties and electronic band structures for Se-doped Co 3 SnInS 2 were examined. The parent compound of this material (Co 3 Sn 2 S 2 ) has two kinds of Sn sites (Sn1 and Sn2 sites). The density functional theory (DFT) calculations show that the indium substitution at the Sn2 site induces a metallic band structure, on the other hand, a semiconducting band structure is obtained from substitution at the Sn1 site. However, according to the previous reports, since the indium atom prefers to replace the tin atom at the Sn1 site rather than the Sn2 site, the resistivity of Co 3 SnInS 2 shows semiconducting-like behavior. In this study we have demonstrated that metallic behavior and a decrease in resistivity for Se-doped Co 3 SnInS 2 occurs without suppression of the Seebeck coefficient. From the DFT calculations, when the selenium content is above 0.5, the total crystallographic energy shows that a higher indium occupancy at Sn2 site is more stable. Therefore, it is suggested that the selenium doping suppress the site preference for indium substitution. This is one of the possible explanations for the metallic conductivity observed in Se-doped Co 3 SnInS 2 [ABSTRACT FROM AUTHOR]

Kesterite semiconductors, particularly Cu2ZnSnS4 (CZTS), have attracted attention for thin-film solar cells. We investigate the incorporation of Fe into CZTS to form the Cu2(Zn,Fe)SnS4 solid-solution for tuning the lattice spacing and band gap. First-principles calculations confirm a phase transition from kesterite (Zn-rich) to stannite (Fe-rich) at Fe/Zn∼0:4. The exothermic enthalpy of mixing is consistent with the high solubility of Fe in the lattice. There is a linear band-gap bowing for each phase, which results in a blue-shift of photo-absorption for Fe-rich alloys due to the confinement of the conduction states. We propose compositions optimal for Si tandem cells. [ABSTRACT FROM AUTHOR]

In this Article, we elucidate the structural and thermoelectric properties of stannite--kuramite solid solutions, Cu2+xFe1-xSnS4-y, (x = 0--1), with sulfur defects (y) ≤ 0.4. Structural analysis revealed that anisotropy decreases and Cu/ Sn disorder increases with an increase in x. The samples with x = 0.8--1 exhibit degenerate conduction, whereas the Seebeck coefficient (S) remains relatively high, S ≈ 100 μV K-1 for x = 0.8 at 300 K. Thermal conductivities (AC) of the solid solutions are in the range 10-3--10-2 W cm-1 K-1, which is close to the K value of silicon dioxide. The dimensionless figure of merit (ZT) reaches 0.044 for x = 0.8 at 300 K. The ZT is enhanced significandy by an increase in temperature and is doubly larger than diat of x = 0 at 300 K. These findings allow us to attain higher ZT values through optimization of chemical composition. [ABSTRACT FROM AUTHOR]

Abstract: We investigated electronic and magnetic nature of A2Co3S2 to reveal two different characteristics of metallic Co–Sn and strongly correlated electronic Co–S bondings. Co 2p X-ray photoelectron spectroscopy (XPS) shows a complicated and mixed-valence like feature with strong satellite. This origin can be explained by two different characteristics of Co–Sn/Co–S bonding nature. This feature is consistent with characteristic electron-density distributions obtained by the maximum-entropy method (MEM)-based pattern fitting analysis and the band calculation. [Copyright &y& Elsevier]

Abstract: We investigated the magnetic and transport properties of polycrystalline to ascertain the magnetism of the new metallic ferromagnet . In magnetization does not saturate up to 5.5T at 10K, and the estimated saturation moment () is small ( per Co atom). In (, the electrical resistivity shows metallic behavior without a hump but has a kink at . The and magnetic susceptibility gradually decrease with increasing x, and there is no antiferromagnetic phase throughout the full range of composition. These results indicate that is a weak itinerant ferromagnet; while, the same order of the Rhodes–Wohlfarth value as suggests the existence of a localized moment. [Copyright &y& Elsevier]

Abstract: We measured transport properties in layered cobalt oxides , that are parent materials of the superconductor , in order to reveal so-far unsettled origin of these electronic and magnetic features. Various sodium nonstoichiometric samples () have been carefully synthesized to control the carrier density and the electronic state of cobalt ions. We found a large negative magnetoresistance (MR) effect in the vicinity of and 1.0. The and 1.0 samples show negative MR, and , respectively, at 90kOe and 4K. These negative MR suggest the pseudogap formation due to the charge ordering in layers, such as and , all of which exhibit similar behaviors. The suppression of the pseudogap by a magnetic field causes the large negative magnetoresistance. [Copyright &y& Elsevier]

A series of polycrystalline samples of Cu2+xFe1-xSnS4-y (x = 0-1, y ≤ 0.4) are prepared by solid state reaction of stoichiometric mixtures of the elements (evacuated silica tubes, 750 °C, 96 h). [ABSTRACT FROM AUTHOR]