Resonant States in the Electronic Structure of the High Performance Thermoelectrics AgPbmSbTe_{m}SbTe_{2+m}$ ; The Role of Ag-Sb Microstructures

Ab initio electronic structure calculations based on gradient corrected density functional theory were performed on a class of novel quaternary compounds AgPb$_{m}SbTe$_{2+m}$, which were found to be excellent high temperature thermoelctrics with large figure of merit ZT ~2.2 at 800K. We find that resonant states appear near the top of the valence and bottom of the conduction bands of bulk PbTe when Ag and Sb replace Pb. These states can be understood in terms of modified Te-Ag(Sb) bonds. Electronic structure near the gap depends sensitively on the microstructural arrangements of Ag-Sb atoms, suggesting that large ZT values may originate from the nature of these ordering arrangements.Comment: Accepted in Physical Review Letter

Nanoscale clusters in the high performance thermoelectric AgPbmSbTem+2

The local structure of the AgPbmSbTem+2 series of thermoelectric materials has been studied using the atomic pair distribution function (PDF) method. Three candidate-models were attempted for the structure of this class of materials using either a one-phase or a two-phase modeling procedure. Combining modeling the PDF with HRTEM data we show that AgPbmSbTem+2 contains nanoscale inclusions with composition close to AgPb3SbTe5 randomly embedded in a PbTe matrix.Comment: 7 pages, 5 figures, 2 tables, submitted to PR

Influence of La 2 Mo 2 O 9 on the sintering behavior and electrochemical properties of gadolinium-doped ceria

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Innovative solid oxide fuel cells based on BaIn 0.3 Ti 0.7 O 2.85 electrolyte and La 2 Mo 2 O 9 amorphous reduced phase as anode material

International audienceThis article presents elaboration of electrolyte-supported solid oxide fuel cells based on the oxide ion conductor BaIn0.3Ti0.7O2.85 (BIT07) as electrolyte, the amorphous reduced phase of La2Mo2O9 (La2Mo2O7-y) as anode which presents a mixed ionic and electronic conduction in low pO2 and La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) as cathode. Electrode materials have been deposited by screen-printing on BIT07 substrate. In order to avoid chemical reactivity between BIT07 and La2Mo2O9, a thin layer of Ce0.9Gd0.1O1.95 (CGO) has been used. Electrochemical performance of the single cell has been characterized by I–V measurements and impedance spectroscopy. Encouraging performance of 40 mW cm−2 at 700 °C is obtained with a thick electrolyte layer. Finally, ageing test of the cell at 700 °C during 800 h has been done with a low rate of performance loss of 4.4 × 10−3% h−1. No degradation of the electrolyte material is reported and stability of the anode material after operating the fuel cell is discussed

Crystal structures of new silver ion conductors Ag7Fe3 (X2O7)4 (X = P, As)

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Toward the Coordination Fingerprint of the Edge-Sharing BO 4 Tetrahedra

International audienceThe K3Sb4BO13 (KSBO) material undergoes an uncommon symmetry increase upon cooling, from triclinic symmetry at room temperature to monoclinic symmetry at low temperature. The first-order phase transition is accompanied by shrinkage of the unit cell, resulting in the transformation of every pair of head-to-tail triangular BO3 groups into one B2O6 unit featuring unique edge-sharing BO4 tetrahedra. This is the first material with B2O6 units formed through temperature lowering and exhibiting a B–O anionic framework composed uniquely of isolated edge-sharing BO4 tetrahedra. Several techniques including single-crystal X-ray diffraction experiments, Raman and 11B magic-angle-spinning NMR spectroscopies, and, for the first time, B K-edge electron energy loss spectroscopy were used to evidence the rare and discrete B2O6 units. The complete transformation of BO3 units into B2O6 units makes the KSBO compound the perfect candidate to extract information about B2O6 units whose signal can be unambiguously assigned

Oxygen Ion Transport and Effects of Doping in Ba 3 Ti 3 O 6 (BO 3 ) 2

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Structural investigation of composite phases Ba1+x[(NaxMn1−x)O3] with x= 2/7, 5/17 and 1/3 ; exotic Mn4.5+ valence in perovskite-like structure

International audienceStructural models are proposed for three composite compounds of chemical formula Ba 1+x[(NaxMn1-x)O3] (x2/7, 5/17 and 1/3) by single crystal X-ray diffraction ; super space formalism is used to obtain an unified description of the three phases. The [(NaxMn1-x)O3] framework is built up from the stacking of face sharing MnO6 octahedra and NaO6 trigonal prisms. The displacive modulations relating to these metallic columns were particularly difficult to modelize. Thus a model, including both discontinuous crenel-like functions for Ba atoms and continuous atomic strings for the Mn/Na sites has finally been retained. The large displacement of the oxygen atoms ( ±0.7 ° A) in comparison with that observed for related compounds ( ±0.3 ° A) makes it a direct consequence of the Na+ alkali insertion inside the trigonal prisms. Owing to this insertion, the Mn atoms exhibit, in the three phases, an ”exotic” oxidation state of about + 4.5

High Performance Dense Proton Ceramic Electrolyte Material Obtained by Cold Sintering Process

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Structural investigation of composite phases Ba1+x[(NaxMn1−x)O3] with x= 2/7, 5/17 and 1/3 ; exotic Mn4.5+ valence in perovskite-like structure

International audienceStructural models are proposed for three composite compounds of chemical formula Ba 1+x[(NaxMn1-x)O3] (x2/7, 5/17 and 1/3) by single crystal X-ray diffraction ; super space formalism is used to obtain an unified description of the three phases. The [(NaxMn1-x)O3] framework is built up from the stacking of face sharing MnO6 octahedra and NaO6 trigonal prisms. The displacive modulations relating to these metallic columns were particularly difficult to modelize. Thus a model, including both discontinuous crenel-like functions for Ba atoms and continuous atomic strings for the Mn/Na sites has finally been retained. The large displacement of the oxygen atoms ( ±0.7 ° A) in comparison with that observed for related compounds ( ±0.3 ° A) makes it a direct consequence of the Na+ alkali insertion inside the trigonal prisms. Owing to this insertion, the Mn atoms exhibit, in the three phases, an ”exotic” oxidation state of about + 4.5