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Transport properties of CeO0.85F0.15SbS2 and undoped CeOSbS2 under high pressure were investigated experimentally and theoretically. Electrical resistivity measurements of the CeO0.85F0.15SbS2 single crystals were performed under various high pressures using a diamond anvil cell with boron-doped diamond electrodes. The samples showed the insulator to metal transition by applying a high pressure up to 30-40 GPa. On the other hand, the undoped CeOSbS2 showed almost the same transport property with the F-doped sample under high pressure. The valence state analysis using X-ray photoelectron spectroscopy revealed a simple valence state of Ce3+ in CeO0.85F0.15SbS2 and mixed valence state between Ce3+ and Ce4+ in undoped CeOSbS2. The valence fluctuation in Ce carried out the comparable transport nature in both samples. A band calculation suggests that the undoped CeOSbS2 could be metallic under high pressure of 30 GPa in accordance with the experimental results. A superior thermoelectric property of power factor in CeOSbS2 was estimated under high pressure around 20 GPa in comparison with that of ambient pressure. [ABSTRACT FROM AUTHOR]

The colusite Cu26V2Sn6S32 has high potential as a thermoelectric material at medium-high temperatures because of a large Seebeck coefficient (S ≃ 220 μV/K) and rather small electrical resistivity (ρ ≃ 100 μΩm) at 660 K. To improve the thermoelectric performance, we have tuned the hole carrier density p by substituting Zn for Cu in Cu26-xZnxV2Sn6S32 (x=1-3) and starting with Cu and Sn deficient compositions in Cu26-yV2Sn6S32 (y=1, 2) and Cu26V2Sn6-zS32 (z=0.25-1), respectively. Powder x-ray diffraction and electron-probe microanalysis showed that the Zn-substituted samples and Sn-deficient (z≥0.5) samples are formed in a single phase, whereas the Cu26-yV2Sn6S32 samples are composed of two phases with slightly different compositions. Within these samples, the value of p at 300K varies in the range between 3.6×1020 and 2.8×1021cm-3. The relation between p and S led to the effective mass m* of 4-7m0 for the hole carriers. The large S of the colusite is therefore ascribed to the heavy mass carriers of the valence band top. The decreases in p with x and y reduced the dimensionless thermoelectric figure of merit ZT, whereas the increase in p with z raised ZT from 0.56 (z=0) to 0.62 (z=0.5) at 660 K. [ABSTRACT FROM AUTHOR]

Synchtrotron radiation x-ray photoemission spectroscopy and high-resolution transmission electron microscopy are used for studying Ca-rich Bi-based superconducting whiskers grown by an [Al.sub.2][O.sub.3]-seeded glassy quenched platelet method. The excess [Ca.sup.2+] ions have substituted for the [Sr.sup.2+] sites and the embedded nanocrystalline domains have resulted in structural distorted defects that have worked as strong pinning center.

Using synchrotron radiation x-ray photoemission spectroscopy and high-resolution transmission electron microscopy, we have studied Ca-rich Bi-based superconducting whiskers grown by an Al2O3-seeded glassy quenched platelet method. The Ca-rich Bi-based superconducting whiskers show a high critical current density of 2×105 A/cm2 at 40 K in self-field. We found that excess Ca2+ ions substitute for the Sr2+ sites and cause pillar-shaped nanocrystalline domains with shorter period modulation embedded in the base crystalline. The embedded nanocrystalline domains can result in structural distorted defects which work as strong pinning center. [ABSTRACT FROM AUTHOR]

Transport properties of CeO0.85F0.15SbS2 and undoped CeOSbS2 under high pressure were investigated experimentally and theoretically. Electrical resistivity measurements of the CeO0.85F0.15SbS2 single crystals were performed under various high pressures using a diamond anvil cell with boron-doped diamond electrodes. The samples showed the insulator to metal transition by applying a high pressure up to 30-40 GPa. On the other hand, the undoped CeOSbS2 showed almost the same transport property with the F-doped sample under high pressure. The valence state analysis using X-ray photoelectron spectroscopy revealed a simple valence state of Ce3+ in CeO0.85F0.15SbS2 and mixed valence state between Ce3+ and Ce4+ in undoped CeOSbS2. The valence fluctuation in Ce carried out the comparable transport nature in both samples. A band calculation suggests that the undoped CeOSbS2 could be metallic under high pressure of 30 GPa in accordance with the experimental results. A superior thermoelectric property of power factor in CeOSbS2 was estimated under high pressure around 20 GPa in comparison with that of ambient pressure. [ABSTRACT FROM AUTHOR]