arXiv subjects

Masanori Matoba

Publications and source records attributed to Masanori Matoba.

11 recordsLinked to original sources

arXiv2018

Superconducting transition temperatures in the electronic and magnetic phase diagrams of Sr2VFeAsO3-delta, a superconductor

We elucidate the magnetic phases and superconducting transition temperatures (Tc) in Sr2VFeAsO3-delta (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 superconducting phase in the range 0.031 =< delta =< 0.145 and an antiferromagnetic (AFM) iron sublattice in the range 0.267 =< delta =< 0.664. Mixed-valent vanadium exhibited a dominant AFM phase in 0.031 =< delta =< 0.088, and a partial ferrimagnetic (Ferri.) phase in the range 0.124 =< delta =< 0.664. The Ferri. phase was the most dominant at a delta 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 superconducting phase. This result was attributed to the magnetic phase of vanadium, which dominates the superconductivity of Fe in 21113V. The Tc-delta curve showed two maxima. The smaller and larger of Tc maxima occurred at delta = 0.073 and delta = 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 Tc enhancement in iron-based superconductors.

cond-mat.supr-con↗

arXiv2018

Electrical and Thermal Transport of Layered Bismuth-chalcogenide EuBiS2F at temperatures between 300 and 623 K

We demonstrate the electrical and thermal transport of layered bismuth-based sulfide EuBiS2F from 300 to 623 K. Although significant hybridization between Eu 4f and Bi 6p electrons was reported previously, the carrier transport of the compound is similar to those of F-doped LaBiS2O, at least above 300 K. The lattice thermal conductivity is lower than that of isostructural SrBiS2F, which is attributed to heavier atomic mass of Eu ions.

cond-mat.supr-con↗

arXiv2015

Effect of Sn-substitution on Thermoelectric Properties of Copper-based Sulfide, Famatinite Cu3SbS4

Copper-based sulfide is an attractive material for Earth-abundant thermoelectrics. In this study, we demonstrate the effect of Sn-substitution on the electrical and thermal transport properties of fematinite Cu3SbS4 from 300 to 573 K. The carrier concentration is controlled in the range from 4 \times 10^18 to 8 \times 10^20 cm^-3 by Sn-substitution. The density-of-states effective mass is found to be ~3.0 me, assuming the single parabolic band model. The direct-type optical band gap is ~0.9 eV, which is consistent with the density functional theory calculation. The dimensionless figure of merit reaches 0.1 for Sn-doped samples at 573 K.

cond-mat.mtrl-sci↗

arXiv2015

Electronic structure and transport properties of Cu-deficient kuramite Cu3-xSnS4

Electrical and thermal transport properties of Cu-deficient kuramite Cu3-xSnS4 (CTS) was examined as a possible earth-abundant thermoelectric material. Crystallographic structure of CTS was characterized by partial disorder between Cu and Sn. In contrast to semiconducting electrical transport of related compounds, such as Cu2ZnSnS4 and Cu3SbS4, metallic conduction with an electrical resistivity of 0.4 mohmcm and a carrier concentration of 3 \times 10^21 cm-3 was observed at 300 K. Lattice thermal conductivity was calculated at 2.6 Wm^-1K^-1, which was probably reduced by Cu-deficiency and or partial cation disorder. Density functional theory calculation indicates valence band was composed of hybridization between Cu 3d orbitals and S 3p orbitals.

cond-mat.mtrl-sci↗

arXiv2014

The effect of simultaneous substitution on the electronic band structure and thermoelectric properties of Se-doped Co3SnInS2 with the Kagome lattice

The thermoelectric properties and electronic band structures for Se-doped Co3SnInS2 were examined. The parent compound of this material (Co3Sn2S2) 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 Co3SnInS2 shows semiconducting-like behavior. In this study we have demonstrated that metallic behavior and a decrease in resistivity for Se-doped Co3SnInS2 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 Co3SnInS2

cond-mat.mtrl-sci↗

arXiv2014

Enhancement of thermoelectric properties by Se substitution in layered bismuth-chalcogenide LaOBiS2-xSex

We have investigated the thermoelectric properties of the novel layered bismuth chalcogenides LaOBiS2-xSex. The partial substitution of S by Se produced the enhancement of electrical conductivity (metallic characteristics) in LaOBiS2-xSex. The power factor largely increased with increasing Se concentration. The highest power factor was 4.5 uW/cmK2 at around 470 deg. C for LaOBiS1.2Se0.8. The obtained dimensionless figure-of-merit (ZT) was 0.17 at around 470 deg. C in LaOBiS1.2Se0.8.

cond-mat.mtrl-sci↗

arXiv2014

Effects of the Cu off-stoichiometry on transport properties of wide gap p-type semiconductor, layered oxysulfide LaCuSO

Layered oxysulfide LaCuSO (x = 0-0.03) was prepared to elucidate the effect of Cu off-stoichiometry on their electrical and thermal transport properties. Electrical resistivity drastically decreases down from ~10^5 ohmcm to ~10^-1 ohmcm as a result of Cu deficiency (x = 0.01) at 300 K. Thermal conductivity of the samples at 300 K, which is dominated by lattice components, is estimated to be 2.3(3) Wm^-1K^-1. Stoichiometric LaCuSO has an optical band gap of 3.1 eV, while broad optical absorption at photon energies of approximately 2.1 eV was observed for Cu-deficient samples. Density functional theory calculation suggests that these broad absorption structures probably originate from the in-gap states generated by the sulfur vacancies created to compensate the charge imbalance due to Cu off-stoichiometry. These results clearly demonstrate that Cu deficiency plays a crucial role in determining the electrical transport properties of Cu-based p-type transparent semiconductors.

cond-mat.mtrl-sci↗

arXiv2013

Ferromagnetic Quantum Critical Point Induced by Tuning the Magnetic Dimensionality of the Heavy-Fermion Iron Oxypnictide Ce(Ru$_{1-x}$Fe$_x$)PO

We have performed 31P-NMR measurements of the c-axis-aligned poly-crystal Ce(Ru1-xFex)PO with a two-dimensional layered structure in order to understand the origin of TCurie suppression by Fe substitution. The variation in the magnetic-fluctuation character with respect to x is investigated from the in-plane and out-of plane fluctuations and the relationship between the static spin susceptibility and the in-plane fluctuation. It was found that three-dimensional ferromagnetic (FM) correlations are dominant and give rise to the FM ordering in CeRuPO. The out-of-plane fluctuations are significantly suppressed with increasing x, and it was revealed that the FM fluctuations become two dimensional near a FM quantum critical point (QCP). Our NMR results strongly suggest that a unique FM QCP in Ce(Ru1-xFex)PO is induced by the suppression of the magnetic correlations along the c-axis, which is a different mechanism from that presumed in heavy-fermion compounds.

cond-mat.str-el↗

arXiv2012

Paramagnetic Phase of a Heavy-Fermion Compound, CeFePO, Probed by 57Fe Mössbauer Spectroscopy

57Fe Mössbauer spectroscopy was applied to an iron-based layered compound CeFePO. At temperatures from 9.4 to 293 K, no magnetic splitting was observed in the Mössbauer spectra of CeFePO indicating a paramagnetic phase of the Fe magnetic sublattice. All the spectra were fitted with a small quadrupole splitting, and the Debye temperature of CeFePO was found to be \sim448 K. The isomer shift at room temperature, 0.32 mm/s, was almost equal to those of LnFeAsO (Ln = La, Ce, Sm). Comparing s-electron density using the isomer shifts and unit cell volumes, it was found that the Fe of CeFePO has a similar valence state to other layered iron-based quaternary oxypnictides except LaFePO.

cond-mat.str-el↗

arXiv2011

Analysis of interdiffusion between SmFeAsO0.92F0.08 and metals for ex situ fabrication of superconducting wire

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 shrinking 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 ~4000 A/cm2 at 4.2 K.

cond-mat.supr-con↗

arXiv2011

Effective Ex-Situ Fabrication of F-Doped SmFeAsO Wire for High Transport Critical Current Density

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.

cond-mat.supr-con↗