Search

The thermoelectric transport properties of the van der Waals-type layered rhombohedral SnAs-based compound, EuSn2As2, have been investigated. A densified polycrystalline sample of EuSn2As2 with porosity (ϕ) of 2.4(9) vol.% exhibited a weak orientation to the c-axis for hexagonal coordination system; the weak orientation is parallel (P ∥) to the pressing direction of hot pressing. Measurements of electrical resistivity (ρ), Seebeck coefficient (S), and thermal conductivity (κ) were conducted perpendicular (P ⊥) to the pressing direction. The experimental values of ρ and S exhibit metallic temperature dependence and p-type carrier polarity. The power factor (P) was 0.51(8) mW m−1 K−2 at 673(4) K. Using the Wiedemann–Franz–Lorenz law, the phonon thermal conductivity (κph) was estimated to be 0.4(6) W m−1 K−1 at 673(6) K. The dimensionless figure of merit, ZT, was 0.092(17) at 673(3) K. [ABSTRACT FROM AUTHOR]

The advanced data processing on the edge devices is getting much attention in addition to the performance of cloud computing for big data analysis and artificial intelligence for the advanced cyber-physical systems and Internet of Things. This paper shows the challenges of research and development on disruptive computing which enhance the conventional computing system with high performance and low power consumption. Future R&D challenges in computing technologies involve all technology layers including algorithms, packaging, software, architecture, circuits, devices, and materials. It is important from the perspective of social implementation and efficiency to select technologies suitable for important applications from each technology layer specific to the computing domain and with consideration for the timeline, and to develop technologies through a vertical integration approach. The promoting method of implementing such R&D is also described. [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]

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]

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]

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]

We demonstrate the fabrication of superconducting SmFeAsO1-xFx (Sm-1111) wires by using the ex-situ powder-in-tube technique. Sm-1111 powder and a binder composed of SmF3, samarium arsenide, and iron arsenide were used to synthesize the superconducting core. Although the F content of Sm-1111 is reduced in the process of ex-situ fabrication, the binder compensates by sufficiently supplementing the F content, thereby preventing a decrease in the superconducting transition temperature and a shrinkage of the superconducting volume fraction. Thus, in the superconducting Sm-1111 wire with the binder, the transport critical current density reaches the highest value of ∼4 kA/cm2 at 4.2 K. [ABSTRACT FROM AUTHOR]

The effect of mass anisotropy on the thermoelectric figure of merit in the presence of polar optical phonon (POP) scattering is numerically studied. Electron transport is considered using the linear Boltzmann transport equation. The mass anisotropy is advantageous for the figure of merit along the principal directions of a small effective mass if phonon thermal conductivity is large. Inelasticity plays an essential role in the obtained result. The result is qualitatively different from that for an ionised impurity model. [ABSTRACT FROM AUTHOR]

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]

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]

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]

We elucidate the magnetic phases and superconducting (SC) transition temperatures (T c ) in Sr 2 VFeAsO 3-δ (21113V), an iron-based superconductor with a thick-blocking layer fabricated from a perovskite-related transition metal oxide. At low temperatures (T  <  37.1 K), 21113V exhibited a SC phase in the range 0.031  ⩽  δ  ⩽  0.145 and an antiferromagnetic (AFM) iron sublattice in the range 0.267  ⩽  δ  ⩽  0.664. Mixed-valent vanadium exhibited a dominant AFM phase in 0.031  ⩽  δ  ⩽  0.088, and a partial ferrimagnetic (Ferri.) phase in the range 0.124  ⩽  δ  ⩽  0.664. The Ferri. phase was the most dominant at a δ value of 0.267, showing an AFM phase of Fe at T  <  20 K. Increasing the spontaneous magnetic moments reduced the magnetic shielding volume fraction due to the SC phase. This result was attributed to the magnetic phase of vanadium, which dominates the superconductivity of Fe in 21113V. The T c -δ curve showed two maxima. The smaller and larger of T c maxima occurred at δ  =  0.073 and δ  =  0.145, respectively; the latter resides on the phase boundary between AFM and the partial Ferri. phases of vanadium. 21113V is a useful platform for verifing new mechanisms of T c enhancement in iron-based superconductors.

In this Article, we elucidate the structural and thermoelectric properties of stannite-kuramite solid solutions, Cu(2+x)Fe(1-x)SnS(4-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 (κ) of the solid solutions are in the range 10(-3)-10(-2) W cm(-1) K(-1), which is close to the κ value of silicon dioxide. The dimensionless figure of merit (ZT) reaches 0.044 for x = 0.8 at 300 K. The ZT is enhanced significantly by an increase in temperature and is doubly larger than that of x = 0 at 300 K. These findings allow us to attain higher ZT values through optimization of chemical composition.