Isothermal transport properties and majority-type defects of BaCo(0.70)Fe(0.22)Nb(0.08)O(3-δ).

(Ba,Sr)(Co,Fe)O3-δ based mixed conducting oxides, e.g. (Ba0.5Sr0.5)(Co1-xFex)O3-δ and Ba(Co0.7Fe0.3-xNbx)O3-δ, are promising candidates for oxygen permeable membranes and SOFC cathodes due to their excellent ambipolar conductivities. Despite these excellent properties, however, their mass/charge transport properties have not been fully characterized and hence, their defect structure has not been clearly elucidated. Until now, the majority types of ionic and electronic defects have been regarded as oxygen vacancies and localized holes. Holes, whether localized or not, are acceptable as majority electronic carriers on the basis of the as-measured total conductivity, which is essentially electronic, and electronic thermopower. On the other hand, the proposal of oxygen vacancies as majority ionic carriers lacks solid evidence. In this work, we document all the isothermal transport properties of Ba(Co0.70Fe0.22Nb0.08)O3-δ in terms of a 2 × 2 Onsager transport coefficient matrix and its steady-state electronic thermopower against oxygen activity at elevated temperatures, and determine the valences of Co and Fe via soft X-ray absorption spectroscopy. It turns out that the ionic and electronic defects in majority should be oxygen interstitials and at least two kinds of holes, one free and the other trapped. Furthermore, the lattice molecule should be Ba(Co0.7Fe0.3-xNbx)O2+δ, not Ba(Co0.7Fe0.3-xNbx)O3-δ, to be consistent with all the results observed.

Colloidal solution-processed CuInSe2 solar cells with significantly improved efficiency up to 9% by morphological improvement.

We demonstrate here that an improvement in the green density leads to a great enhancement in the photovoltaic performance of CuInSe2 (CISe) solar cells fabricated with Cu-In nanoparticle precursor films via colloidal solution deposition. Cold-isostatic pressing (CIP) increases the precursor film density by ca. 20%, which results in an appreciable improvement in the microstructural features of the sintered CISe film in terms of a lower porosity, a more uniform surface morphology, and a thinner MoSe2 layer. The low-band-gap (1.0 eV) CISe solar cells with the CIP-treated films exhibit greatly enhanced open-circuit voltage (V(OC), typically from 0.265 to 0.413 V) and fill factor (FF, typically from 0.34 to 0.55), compared to the control devices. As a consequence, an almost 3-fold increase in the average efficiency, from 3.0 to 8.2% (with the highest value of 9.02%), is realized. Diode analysis reveals that the enhanced V(OC) and FF are essentially attributed to the reduced reverse saturation current density and diode ideality factor. This is associated with suppressed recombination, likely due to the reduction in recombination sites at grain/air surfaces, intergranular interfaces, and defective CISe/CdS junctions. From the temperature dependences of V(OC), it is revealed that CIP-treated devices suffer less from interface recombination.

A new high-energy cathode for a Na-ion battery with ultrahigh stability.

Large-scale electric energy storage is a key enabler for the use of renewable energy. Recently, the room-temperature Na-ion battery has been rehighlighted as an alternative low-cost technology for this application. However, significant challenges such as energy density and long-term stability must be addressed. Herein, we introduce a novel cathode material, Na1.5VPO4.8F0.7, for Na-ion batteries. This new material provides an energy density of ~600 Wh kg(-1), the highest value among cathodes, originating from both the multielectron redox reaction (1.2 e(-) per formula unit) and the high potential (~3.8 V vs Na(+)/Na) of the tailored vanadium redox couple (V(3.8+)/V(5+)). Furthermore, an outstanding cycle life (~95% capacity retention for 100 cycles and ~84% for extended 500 cycles) could be achieved, which we attribute to the small volume change (2.9%) upon cycling, the smallest volume change among known Na intercalation cathodes. The open crystal framework with two-dimensional Na diffusional pathways leads to low activation barriers for Na diffusion, enabling excellent rate capability. We believe that this new material can bring the low-cost room-temperature Na-ion battery a step closer to a sustainable large-scale energy storage system.

Electrical conductivity-defect structure correlation of variable-valence and fixed-valence acceptor-doped BaTiO(3) in quenched state.

Insulation resistance degradation of dielectric BaTiO(3) is expected to be closely correlated to its defect structure frozen in from elevated processing temperatures. For BaTiO(3), respectively doped with variable-valence (Mn(Ti)) and fixed-valence acceptors (Al(Ti)), their defect structures were frozen in by quenching at different equilibrium oxygen activities in the range of -18 < log a(O(2))< or = 0 at 1000 and 900 degrees C, respectively, and their electrical conductivities were measured against temperature in the range of 200 < or =T/K < or = 494 by impedance spectroscopy. Frozen-in defect structures were calculated and compared with the conductivity as measured in the quenched state. A close correlation has been confirmed between the bulk conductivity as measured in the quenched state and the frozen-in defect structure as calculated. The effects of variable- and fixed-valence acceptor impurities on the defect structure and electrical conductivity in the quenched state are highlighted in the light of hole trapping, and the charge transport behavior in the quenched state is discussed.