Month: September 2013

Tunable near-infrared and visible-light transmittance in nanocrystal-in-glass composites

nature12398-f1

Anna Llordés, Guillermo Garcia, Jaume Gazquez & Delia J. Milliron

Nature 500, 323–326

doi:10.1038/nature12398

Amorphous metal oxides are useful in optical, electronic and electrochemical devices. The bonding arrangement within these glasses largely determines their properties, yet it remains a challenge to manipulate their structures in a controlled manner. Recently, we developed synthetic protocols for incorporating nanocrystals that are covalently bonded into amorphous materials. This ‘nanocrystal-in-glass’ approach not only combines two functional components in one material, but also the covalent link enables us to manipulate the glass structure to change its properties. Here we illustrate the power of this approach by introducing tin-doped indium oxide nanocrystals into niobium oxide glass (NbOx), and realize a new amorphous structure as a consequence of linking it to the nanocrystals. The resulting material demonstrates a previously unrealized optical switching behaviour that will enable the dynamic control of solar radiation transmittance through windows. These transparent films can block near-infrared and visible light selectively and independently by varying the applied electrochemical voltage over a range of 2.5 volts. We also show that the reconstructed NbOx glass has superior properties—its optical contrast is enhanced fivefold and it has excellent electrochemical stability, with 96 per cent of charge capacity retained after 2,000 cycles.

Thermal analysis for low temperature synthesis of oxide thin films from chemical solutions

jp-2013-049742_0006

D. Sanchez-Rodriguez, J. Farjas, P Roura, S. Ricart, N. Mestres Andreu, X. Obradors and T. Puig

Journal of Physical Chemistry C 117, 20133-20138 (2013)

DOI: 10.1021/jp4049742

The possibility of synthesizing functional oxide thin films at low temperature via combustion synthesis is analyzed both experimentally and numerically. To this aim, the decomposition of several oxide precursors [copper and cerium acetates, yttrium trifluoroacetate, and In2O3 and La0.7Sr0.3MnO3 (LSMO) nitrate based precursors] has been analyzed by thermal analysis techniques. It is shown that, although these precursors decompose via combustion when they are in the form of powders, their corresponding films show no evidence of combustion. The reason for this different behavior is clearly revealed with numerical simulations. Thin films will hardly experience combustion because the precursor front extinguishes before reaching the precursor–substrate interface leaving a “cool zone” hundreds of micrometers thick. In contrast, it is argued that thin oxide films can be obtained at temperatures lower than powders because of the enhanced gas transport mechanisms that usually limit the decomposition rate.

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