Ternary selenide CuAgSe shows a great potential as a new promising thermoelectric material due to the superior carrier mobility and low lattice thermal conductivity. In this study, we doped Te at Se-sites and systematically studied the effect of Te-doping on the thermoelectric properties of low-temperature CuAgSe phase (β-CuAgSe). It is found that the Te doping limit in β-CuAgSe is around 0.15. The longitudinal resistivity and Hall resistivity measurements under magnetic field suggest that Te-doping exerts little effect on the band structure and the low-mobility carriers (holes) contribute weakly to the electrical transports in all Te-doped samples. Thus, the p-n transition and accompanying abrupt Seebeck coefficient decrease at elevated temperature, which are quite common in the non-stoichiometric β-CuAgSe samples, were not observed in Te-doped samples. Although the electrical conductivity of Te-doped samples is reduced due to the decreased carrier concentration and mobility, the significantly decreased thermal conductivity ensures the Te-doped samples still maintaining similar or slightly higher thermoelectric figure of merit (zT) as compared with that of the stoichiometric β-CuAgSe. The maximum zT around 0.7 at 450 K is obtained in CuAgSe0.95Te0.05.

We have performed polarized Raman scattering measurements on the newly discovered superconductor Nd(O,F)BiS2 (Tc = 4 K). We observe 2 Raman active modes, with frequencies in accordance with first-principles calculations. One A1g phonon mode at 112.4 cm −1 exhibits a Fano line shape due to electron-phonon coupling. We find a resonance for this mode at 2.45 eV excitation energy. We estimate a 0.68 contribution of this mode to the electron-phonon coupling constant λ. Our Raman results suggest that the BiS2-based superconductors are possibly phonon-mediated BCS superconductors. 74.25.nd, 74.25.Kc, Despite low superconducting (SC) critical temperatures (T c 's) of 3 K -10 K in Bi 4 O 4 S 3 and (La/Nd/Ce/Pr)O 0.5 F 0.5 BiS 2 [1-11], the BiS 2 -based superconductors are often regarded as possible hightemperature superconductor candidates. Indeed, their square BiS 2 layers are quite similar to the CuO 2 layers in high-T c cuprate superconductors [12] and the FeAs planes in the iron-based superconductors [13]. First-principles calculations [14,15] indicate that LaO 0.5 F 0.5 BiS 2 evolves from a band insulator to a bad metal upon doping. Interestingly, a large electron-phonon coupling constant λ = 0.85 is predicted, leading to a T c value of 10.6 K from the Allen-Dynes formula [16,17] that is compatible with experiments, suggesting a phonon-mediated pairing mechanism. Recent angle-resolved photoemission spectroscopy (ARPES) data were also interpreted in terms of the presence of polarons [18]. However, a neutron scattering work [19] suggests that the electronphonon coupling in LaO 0.5 F 0.5 BiS 2 is weaker than expected and a strong SC paring exceeding the limit of simple phonon mediated scenarios was proposed from upper critical field and magnetoresistance measurements [20]. Consequently, whether phonons are the paring glue for the BiS 2 -based superconductors is still under debate.In this paper we use Raman scattering to investigate directly the crystallographic structure and the electronphonon coupling in Nd(O,F)BiS 2 single-crystals. We report 2 Raman active modes, with frequencies in accordance with first-principles calculations. A photon energy resonance at about 2.45 eV for the 112.4 cm −1 phonon mode is observed and assigned to an electronic transition. The asymmetric phonon spectral profile of this mode indicates a strong electron-phonon coupling and suggests that phonons are possibly the paring glue in the BiS 2based superconductors. * p.richard@iphy.ac.cn † dingh@iphy.ac.cnThe Nd(O,F)BiS 2 single-crystals used in our Raman scattering measurements were grown by a flux method with KCl/LiCl as the flux [21]. Energy-dispersive X-ray spectroscopy (EDX) measurements performed on several pieces of samples with T c = 4 K give an averaged compo-The crystals were cleaved in air to obtain flat surfaces and then quickly transferred into a low-temperature cryostat ST500 (Janis) for the Raman measurements between 5 and 300 K under a working vacuum better than 2 × 10 −6 mbar. Raman scattering measurements were performed using...

Near infrared (NIR) lasers, as a new excitation source for Raman spectroscopy, has shown its unique advantages and is being increasingly used for some special samples, such as those emitting strong fluorescence in the visible region. This article focuses on some issues related to high-pressure micro-Raman spectroscopy using NIR excitation source. The Raman spectra of 4:1 methanol–ethanol mixture (4:1 M–E) show a linear variation in both Raman shifts and linewidths under pressure up to 18 GPa. This result is useful in distinguishing Raman scattering of samples from that of the alcohol mixture, an extensively used pressure-transmitting medium. The R1 fluorescence in the red region induced by two-photon absorption of the NIR laser is strong enough to be used as pressure scale. The frequency and line width of the R1 lines are very sensitive to pressure change and the glass transition of the pressure medium. Our results manifest that it is reliable and convenient to use NIR induced two-photon excited fluorescence of ruby for both pressure calibration and distribution of pressure in the 4:1 M–E pressure transmitting medium.