arXiv subjects

Tetsuo Irifune

Publications and source records attributed to Tetsuo Irifune.

25 records · Page 2Linked to original sources

arXiv2018

Data-driven Exploration of New Pressure-induced Superconductivity in PbBi$_2$Te$_4$ with Two Transition Temperatures

Candidates compounds for new thermoelectric and superconducting materials, which have narrow band gap and flat bands near band edges, were exhaustively searched by the high-throughput first-principles calculation from an inorganic materials database named AtomWork. We focused on PbBi$_2$Te$_4$ which has the similar electronic band structure and the same crystal structure with those of a pressure-induced superconductor SnBi2Se4 explored by the same data-driven approach. The PbBi$_2$Te$_4$ was successfully synthesized as single crystals using a melt and slow cooling method. The core level X-ray photoelectron spectroscopy analysis revealed Pb2+, Bi3+ and Te2- valence states in PbBi$_2$Te$_4$. The thermoelectric properties of the PbBi$_2$Te$_4$ sample were measured at ambient pressure and the electrical resistivity was also evaluated under high pressure using a diamond anvil cell with boron-doped diamond electrodes. The resistivity decreased with increase of the pressure, and two pressure-induced superconducting transitions were discovered at 3.4 K under 13.3 GPa and at 8.4 K under 21.7 GPa. The data-driven approach shows promising power to accelerate the discovery of new thermoelectric and superconducting materials.

cond-mat.supr-con↗

arXiv2018

Pressure-induced Superconductivity in Sulfur-doped SnSe Single Crystal Using Boron-doped Diamond Electrode-prefabricated Diamond Anvil Cell

Sulfur-doped SnSe single crystal was successfully synthesized using a melt and slow-cooling method. The chemical composition and valence state of the obtained sample were analyzed by X-ray photoelectron spectroscopy. The pressure range of a diamond anvil cell with boron-doped diamond electrodes was upgraded to 104 GPa using nano-polycrystalline diamond anvil to investigate a pressure effect for the sample. Electrical resistivity measurements of sulfur-doped SnSe single crystal showed the insulator-metal-superconductor transition by applying high pressure up to 75.9 GPa.

cond-mat.supr-con↗

arXiv2018

Diamond anvil cell using boron-doped diamond electrodes covered with undoped diamond insulating layer

Diamond anvil cell using boron-doped metallic diamond electrodes covered with undoped diamond insulating layer have been developed for electrical transport measurements under high pressure. These designed diamonds were grown on a bottom diamond anvil via a nanofabrication process combining microwave plasma-assisted chemical vapor deposition and electron beam lithography. The resistance measurements of high quality FeSe superconducting single crystal under high pressure were successfully demonstrated by just putting the sample and gasket on the bottom diamond anvil directly. The superconducting transition temperature of FeSe single crystal was enhanced up to 43 K by applying uniaxial-like pressure.

cond-mat.supr-con↗

arXiv2016

Universal amorphous-amorphous transition in GexSe1-x glasses under pressure

Pressure induced structural modifications in vitreous Ge$_{x}$Se$_{100-x}$ (where 10 $\leq$ x $\leq$ 25)are investigated using X-ray absorption spectroscopy (XAS) along with supplementary X-ray diffraction (XRD) experiments and ab initio molecular dynamics (AIMD) simulations. Universal changes in distances and angle distributions are observed when scaled to reduced densities. All compositions are observed to remain amorphous under pressure values up to 42 GPa. The Ge-Se interatomic distances extracted from XAS data show a two-step response to the applied pressure; a gradual decrease followed by an increase at around 15-20 GPa, depending on the composition. This increase is attributed to the metallization event that can be traced with the red shift in Ge K edge energy which is also identified by the principal peak position of the structure factor. The densification mechanisms are studied in details by means of AIMD simulations and compared to the experimental results. The evolution of bond angle distributions, interatomic distances and coordination numbers are examined and lead to similar pressure-induced structural changes for any composition.

cond-mat.mtrl-sci↗

arXiv2016

Local Structure and Spin Transition in Fe2O3 Hematite at High-Pressure

The pressure evolution of the local structure of Fe2O3 hematite has been determined for the first time by extended x-ray absorption fine structure up to 79 GPa. The comparison to the different high-pressure forms proposed in the literature suggests that the orthorhombic structure with space group Aba2 is the most probable. The crossover from Fe high-spin to low-spin states with pressure increase has been monitored from the pre-edge region of the Fe K-edge absorption spectra. The "simultaneous" comparison with the local structural changes allows us to definitively conclude that it is the electronic transition that drives the structural transition and not viceversa.

cond-mat.mtrl-sci↗

arXiv2012

Polycrystalline γ-boron: As hard as polycrystalline cubic boron nitride

The Vickers hardness of polycrystalline γ-B was measured using a diamond indentation method. The elastic properties of polycrystalline γ-B (B=213.9 GPa, G=227.2 GPa, and E=503.3 GPa) were determined using ultrasonic measurement at ambient condition. Under the loading force up to 20 N, our test gave an average Vickers hardness in the asymptotic-hardness region of 30.3 GPa. The average fracture toughness was measured as 4.1MPa m1/2. Additionally, We also measured the hardness and elastic properties of polycrystalline β-B and PcBN for comparison. The hardness and elastic properties for polycrystalline γ-B was found to be very close to that of PcBN. Our results suggest that the polycrystalline γ-B could be a superhard polycrystalline material for industrial applications.

cond-mat.mtrl-sci↗

arXiv2011

Phase relations in boron at pressure up to 18 GPa and temperature up to 2200 °C

The phase relations in boron have been investigated at high pressure and high temperature using a multianvil apparatus, and the quenched sample has been analyzed by x-ray diffraction, Raman spectra and transmission electron microscopy. We demonstrate that γ-B28 can be synthesized over a wide P-T range, and T-B50 is obtained at higher temperatures and similar pressures. The phase boundary of the β-B106, γ-B28 and T-B50 is determined at pressures between 7 and 18 GPa and the temperatures of 500-2200 °C. The results suggest that T-B50 might be an intermediate phase-metastable, formed for kinetic reasons (Ostwald rule) on the way from β-B106 to T-192 and γ-B28 to T-192.

cond-mat.mtrl-sci↗