Electronic phase diagram of NdFe1-xRhxAsO

We report on the electrical resistivity, thermoelectric power and electronic phase diagram of rhodium-doped NdFeAsO. Rhodium doping suppresses the structural phase transition and spin density wave observed in the undoped material, and superconductivity emerges at x close to 0.05, despite the distortion of FeAs4 tetrahedra induced by the large size difference between Rh and Fe elements. The Tc(x) curve is dome-like, and the highest Tc is reached at x = 0.1, with Tconset = 18K. An upturn of the electrical resistivity above Tc has been observed, with a Kondo like behaviour above Tc and a Fermi-liquid behaviour close to room temperature.Comment: 17 pages, 10 figure

Electronic phase diagram of NdFe1-xRhxAsO

We report on the electrical resistivity, thermoelectric power and electronic phase diagram of rhodium-doped NdFeAsO. Rhodium doping suppresses the structural phase transition and spin density wave observed in the undoped material, and superconductivity emerges at x close to 0.05, despite the distortion of FeAs4 tetrahedra induced by the large size difference between Rh and Fe elements. The Tc(x) curve is dome-like, and the highest Tc is reached at x = 0.1, with Tconset = 18K. An upturn of the electrical resistivity above Tc has been observed, with a Kondo like behaviour above Tc and a Fermi-liquid behaviour close to room temperature.Comment: 17 pages, 10 figure

Structure and Transport Properties of the BiCuSeO-BiCuSO Solid Solution

In this paper, we report on the crystal structure and the electrical and thermal transport properties of the BiCuSe1−xSxO series. From the evolution of the structural parameters with the substitution rate, we can confidently conclude that a complete solid solution exists between the BiCuSeO and BiCuSO end members, without any miscibility gap. However, the decrease of the stability of the materials when increasing the sulfur fraction, with a simultaneous volatilization, makes it difficult to obtain S-rich samples in a single phase. The band gap of the materials linearly increases between 0.8 eV for BiCuSeO and 1.1 eV in BiCuSO, and the covalent character of the Cu-Ch (Ch = chalcogen element, namely S or Se here) bond slightly decreases when increasing the sulfur fraction. The thermal conductivity of the end members is nearly the same, but a significant decrease is observed for the samples belonging to the solid solution, which can be explained by point defect scattering due to atomic mass and radii fluctuations between Se and S. When increasing the sulfur fraction, the electrical resistivity of the samples strongly increases, which could be linked to an evolution of the energy of formation of copper vacancies, which act as acceptor dopants in these materials

Étude de skutterudites de terres-rares (R) et de métaux d (M) du type RM4Sb12 (de nouveaux matériaux thermoélectriques pour la génération d'électricité)

Cette étude présente les propriétés de nouveaux composés de la famille des skutterudites,de formule générale (R et R' Ce, Yb, Ba, La). La valence de Yb est non entière et elle décroît lorsque la fraction de Yb augmente tandis que Ce est toujours trivalent. Le moment parama a été décomposé suivant les sous-systèmes R, R' et Fe La contribution de ce dernier ne dépend pas la nature et de la valence de R et R', mais elle décroît si Fe est substitué par Ni. Une transition ma est présente pour R = Yb et Ba à 6,5 K sans doute vers un état verre de spin. Les propriétés de transport électrique et thermique ont été mesurées de 5K à 800K ce qui a permis de discuter des potentialités de ces matériaux pour la génération d'électricité par effet thermoélectrique. Le facteur de puissance et le facteur de mérite sont plus élevés dans les composés de type Ce que dans ceux de type R présentés dans la littérature.We have studied the properties of ii tterudi compounds, with general formula RypR'pFe (R and R' = Ce, Yb, Ba, La). X-ray absorption spectroscopy shows that Ce is aiways in a trivalent state and that Yb valence decreases as Yb fraction increases. The parama effective moment has been separated into contributions arisin from R, R' and Fe The latest does not depend on the nature of R and R' and oftheir valence states. However, it decreases when Fe is substituted by Ni. A ma.gnetic transition as been observed for R Yb and Ba at 6,5 K, which seems to be of spin-glass nature. The electrical and thermal properties have been measured between 5K and 800K, and the potentialities of these compounds for thermoelectric power generation have been discussed. The power factor and the figure of ment ZT have been improved significantly in double filled CeY/2Yb skutterudites as compared to the R seriesPARIS12-CRETEIL BU Multidisc. (940282102) / SudocSudocFranceF

Synthesis and transport properties of p-type lead-free AgSnmSbSe2Tem thermoelectric systems

We report the synthesis, characterization and thermoelectric properties of lead-free AgSnmSbSe2Tem (m = 2 and 10) systems. Powder X-ray diffraction patterns and Rietveld refinement results were consistent with phases belonging to the Pm (3) over barm space group. The microstructures and morphologies of these systems were investigated using scanning electron microcopy (SEM) and high-resolution transmission electron microscopy (HRTEM). Parallelepiped bars for transport measurements were prepared using two methods: the classical method (CM) from melted samples and the spark plasma sintering (SPS). The AgSnmSbSe2Tem (m = 2 and 10) systems exhibited typical degenerate semiconductor behavior, with a carrier concentration of approximately +10(21) cm(-3). We determined that the Seebeck coefficient can be substantially increased from approximately +40 V K-1 (CM) to +70 mu V K-1 (SPS) in AgSn2SbSe2Te2 at room temperature. Consequently, the power factor (S(2)cr) was similar to 22 W cm(-1) K-2. On the basis of the electrical and thermal transport properties, ZT values of similar to 0.10 were obtained at room temperature. (C) 2018 Elsevier B.V. All rights reserved.Entidad financiadora FONDECYT Número de concesión 116068

Amplified Photoluminescence of CsPbX3 Perovskites Confined in Silica Film with a Chiral Nematic Structure

Metal halide perovskites (MHPs, CsPbX3: X = Cl, Br, I) have advanced the field of optoelectronic devices due to their remarkable light-emitting capabilities, stemming from the large overlap between their emission and absorption spectra, offering the possibility to reabsorb their own emitted photons. Herein, a straightforward method is reported to confine CsPbBr into mesoporous silica films with a chiral nematic structure, allowing the amplification of the photoluminescence (PL). The simple room temperature ligand-free synthesis allows facile growth of CsPbBr in silica photonic films, in which the Bragg peak position can be tuned from the UV to the visible range. The perovskite/silica films demonstrate a remarkable improvement in PL intensity and lifetime compared to the as-synthesized non-confined perovskite nanocrystals (NCs) due to the overlap of the Bragg peak position of the chiral nematic photonic films and CsPbBr absorption band. Such a PL enhancement stems from the slow photon effect induced at blue and red Bragg peak edges that facilitates the photon recycling of the emitted photons. This innovative approach offers a new way to fabricate highly emissive and long-lived photoluminescent films at ambient conditions, potentially advancing perovskite utilization in light-emitting devices

Structure and Transport Properties of the BiCuSeO-BiCuSO Solid Solution

In this paper, we report on the crystal structure and the electrical and thermal transport properties of the BiCuSe1−xSxO series. From the evolution of the structural parameters with the substitution rate, we can confidently conclude that a complete solid solution exists between the BiCuSeO and BiCuSO end members, without any miscibility gap. However, the decrease of the stability of the materials when increasing the sulfur fraction, with a simultaneous volatilization, makes it difficult to obtain S-rich samples in a single phase. The band gap of the materials linearly increases between 0.8 eV for BiCuSeO and 1.1 eV in BiCuSO, and the covalent character of the Cu-Ch (Ch = chalcogen element, namely S or Se here) bond slightly decreases when increasing the sulfur fraction. The thermal conductivity of the end members is nearly the same, but a significant decrease is observed for the samples belonging to the solid solution, which can be explained by point defect scattering due to atomic mass and radii fluctuations between Se and S. When increasing the sulfur fraction, the electrical resistivity of the samples strongly increases, which could be linked to an evolution of the energy of formation of copper vacancies, which act as acceptor dopants in these materials