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The misfit-layered cobalt oxide [Ca2CoO3-δ][CoO2]1.62 is a promising material for high-temperature thermoelectric heat recovery. Here, we show that discrepancies in the numerously reported thermoelectric performances can result from Co3OM4 impurities or a change of the defects, i.e., the relative Co content in the [Ca2CoO3-δ][CoO2]1.62 phase. We observe that increasing the relative Co content in the [Ca2CoO3-δ][CoO2]1.62 phase leads to a larger figure of merit ZT. We attribute this increase of ZT to additional p-type charge carriers introduced by Ca vacancies and the resulting reduction of the electrical resistivity. For Co/Ca ratios above the miscibility limit, the increase in thermal conductivity due to the formation of Co3OM4 impurities leads to a reduction of ZT when the volume fraction of the Co3OM4 phase is increased from 1% to 3%. Hence, the best figure of merit is expected close to the upper phase boundary of the [Ca2CoO3-δ][CoO2]1.62 phase. [ABSTRACT FROM AUTHOR]

Polycrystalline tungsten-substituted CaMn1-xWxO3-δ (0.00 ≤ x ≤ 0.05) powders were synthesized from a polymeric precursor, pressed and sintered to high density. The impact of tungsten substitution on the crystal structure, thermal stability, phase transition, electronic and thermal transport properties is assessed. Tungsten acts as an electron donator and strongly affects high-temperature oxygen stoichiometry. Oxygen vacancies form in the high figure-of-merit (ZT)-region starting from about T = 1000 K and dominate the carrier concentration and electronic transport far more than the tungsten substitution. The analysis of the transport properties yields that in the investigated regime the band filling is sufficiently high to overcome barriers of polaron transport. Therefore, the Cutler-Mott approach describes the electrical transport more accurately than the Mott approach for small polaron transport. The lattice thermal conductivity near room temperature is strongly suppressed with increasing tungsten concentration due to mass-difference impurity scattering. A ZT of 0.25 was found for x = 0.04 at 1225 K. [ABSTRACT FROM AUTHOR]

We assess the benefits of offline laser-desorption/ionization mass spectrometry in understanding ambient particulate matter (PM) sources. The technique was optimized for measuring PM collected on quartz-fiber filters using silver nitrate as an internal standard for m∕z calibration. This is the first application of this technique to samples collected at nine sites in central Europe throughout the entire year of 2013 (819 samples). Different PM sources were identified by positive matrix factorization (PMF) including also concomitant measurements (such as NOx, levoglucosan, and temperature). By comparison to reference mass spectral signatures from laboratory wood burning experiments as well as samples from a traffic tunnel, three biomass burning factors and two traffic factors were identified. The wood burning factors could be linked to the burning conditions; the factors related to inefficient burns had a larger impact on air quality in southern Alpine valleys than in northern Switzerland. The traffic factors were identified as primary tailpipe exhaust and most possibly aged/secondary traffic emissions. The latter attribution was supported by radiocarbon analyses of both the organic and elemental carbon. Besides these sources, factors related to secondary organic aerosol were also separated. The contribution of the wood burning emissions based on LDI-PMF (laser-desorption/ionization PMF) correlates well with that based on AMS-PMF (aerosol mass spectrometer PMF) analyses, while the comparison between the two techniques for other components is more complex. [ABSTRACT FROM AUTHOR]

We assess the benefits of offline laser-desorption/ionization mass spectrometry (LDI-MS) in understanding ambient particulate matter (PM) sources. The technique was optimized for measuring PM collected on quartz-fiber filters using silver nitrate as an internal standard for m/z calibration. This is the first application of this technique to samples collected at nine sites in central Europe throughout the entire year 2013 (819 samples). Different PM sources were identified by positive matrix factorization (PMF) including also concomitant measurements (such as NOx, levoglucosan, and temperature). By comparison to reference mass spectral signatures from laboratory wood burning experiments as well as samples from a traffic tunnel, three biomass-burning factors and two traffic factors were identified. The wood-burning factors could be linked to the burning conditions; the factors related to inefficient burns had a larger impact on air quality in southern Alpine valleys than in northern Switzerland. The traffic factors were identified as primary tailpipe exhaust and most possibly aged/secondary traffic emissions, respectively. The latter attribution was supported by radiocarbon analyses of both the organic and elemental carbon. Besides these sources, also factors related to secondary organic aerosol were separated. The contribution of the wood burning emissions based on LDI-PMF correlates well with that based on AMS-PMF analyses, while the comparison between the two techniques for other components is more complex. [ABSTRACT FROM AUTHOR]

Large-grained CuInSe2 absorber layers are synthesized using a non-vacuum process based on nanoparticle ink precursors and selenization by rapid thermal processing (RTP). The use of hydroxide-based particles in organic solvents allows for the conversion with elemental selenium without the need to employ explosive and/or toxic H2 or H2Se gasses. Lateral grain sizes up to 4 µm are obtained through a novel RTP route, overcoming the inherently high layer porosity for previous nanoparticle processes. Morphological and elemental characterization at interrupted selenization steps suggests that liquid selenium can play a beneficial role in promoting layer densification and grain growth. Long carrier collection lengths in CuInSe2 enable notable conversion efficiencies, despite the low minority carrier lifetimes of below 1 ns. Record efficiencies up to 8.73% highlight the potential of low-cost, non-vacuum deposition of chalcopyrite absorber layers with safe and simple precursors and processing routes. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Perovskite-type LaVO2.78N0.10 powder was synthesized by thermal ammonolysis of the oxide precursor LaVO4. By X-ray, neutron, and electron diffraction an orthorhombic crystal structure with space group Pnma was identified. XANES spectra showed that the oxidation state of vanadium changes from 5+ in LaVO4 to approximately 3+ in LaVO2.78N0.10. The temperature dependence of the electrical conductivity revealed an Arrhenius-type behavior with an activation energy of 0.103 eV in the temperature range of 119-302 K indicating that the conduction process is thermally activated band transition. Based on the positive Seebeck coefficient, holes were identified as the dominant charge carriers in the temperature range of 100-302 K. Both the Seebeck coefficient and the thermal conductivity showed an anomaly at 138 K, which is attributed to the Néel temperature for antiferromagnetic ordering according to magnetic susceptibility measurements. [ABSTRACT FROM AUTHOR]

ABSTRACT Non-vacuum methods for Cu(In,Ga)Se2 (CIGS) absorber deposition have gained wide interest because of their inherent cost and energy saving potential. Here, a solution-based processing route for CIGS absorber layers is presented that employs binder-free solutions of metal salts in non-toxic, alcohol solvents. Despite the low-boiling-point nature of the employed solvents, a residual carbon-rich layer is observed between the CIGS and metal back contact. Based on comprehensive investigations by scanning electron microscopy, energy-/wavelength dispersive X-ray spectroscopy, X-ray fluorescence, X-ray diffraction, thermogravimetric analysis, differential thermal analysis, and extended X-ray absorption fine structure spectroscopy, a formation reaction mechanism through intermediate metal-organic complexes is proposed. In this route, the CIGS layer is formed in selenium atmosphere via a gradual decomposition of the carbon-rich layer comprising carboxylic chelate complexes of metals. A compositional gradient occurs in the CIGS absorber, whereas a significant amount of metals remains in the carbon-rich layer. The incorporation of Ga into CIGS is affected by the initial salt concentration and the selenization temperature. Fabricated solar cells exhibit active area efficiencies of up to 7.7% on 0.3 cm2 area without anti-reflection coating, which is among the highest reported efficiencies for solar cells from a solution process with non-explosive gases or solvents. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Oxygen contents and thermoelectric properties of hot-pressed polycrystalline Ca3−x Bi x Co4O9+δ (0.00 < x < 0.20) samples were investigated both in Ar and air atmospheres in the temperature range 300 K < T < 870 K. Ar-annealed samples showed reduction in electrical conductivity and an elevation in Seebeck coefficient at T > 650 K with increasing x, whereas no systematic behaviour was found for the air-annealed samples. The figure-of-merit ZT at 870 K was improved from 0.12 (x = 0.00, both air and Ar) to 0.19 (x = 0.20, air) and 0.15 (x = 0.20, Ar). The results mark the significance of the oxygen content when assessing the thermoelectric properties of oxide compounds. [Copyright &y& Elsevier]

Abstract: Topotactic oxygen deintercalation from cubic perovskite oxide SrCoO3− δ (δ <0.25) is realized in a controlled way at low temperatures. Annealing in air at 200< T <275°C results in a three-phase region within 0.25< δ <0.50. Two of the phases are known previously, namely SrCoO2.5, a phase with an orthorhombic brownmillerite-type (BM) structure, and SrCoO2.75 (T1), a phase with a slight tetragonal distortion from cubic symmetry. The third phase (T2) has a strong tetragonal distortion, and appears to be the missing n =3 member of the SrCoO(3n −1)/n series. Once the overall oxygen content reaches the value of (3− δ)aver =2.68(1), the T1-to-T2 phase conversion proceeds at constant (3− δ)aver. A more pronounced evolution of the c T2 lattice parameter as compared to the a T2 parameter implies a layered oxygen-vacancy-ordered structure for T2 with some flexibility for oxygen-content variation, in the style of the BM phase. [Copyright &y& Elsevier]