Highly ordered TiO(2) nanotubes were successfully fabricated using a nanoporous alumina templating method. A modified sol-gel route was used to infiltrate the alumina pores with Ti(OC(3)H(7))(4) which was subsequently converted into TiO(2) nanotubes. The average external diameter, tube lengths, and wall thickness achieved were 295 nm, 6-15 microm, and 21-42 nm, respectively. Diffraction data reveals that the nanotubes consist solely of the anatase phase. Dye-sensitized solar cells using TiO(2) nanotube arrays as the working electrode yielded power conversion efficiencies as high as 3.5% with a maximum incident photon-to-current conversion efficiency of 20% at 520 nm.
A new series of Na ion conductors of the type Na5MSi4012, where M = Fe, In, Sc, Y, and the rare earths Lu-Sm, has been prepared by hydrothermal and solid-state reactions. Na ion conductivities, measured with Na electrodes at ~103 Hz, are proportional to the size of M3+ and range from 2 X 10~3 ( cm)"1 for Na5ScSi4012 to 3 X 10"1 ( cm)"1 at 300 °C for Na5SmSi4012. This behavior is consistent with a structure consisting of Sil2036 rings stacked to form columns held apart by M06 octahedra. Immobile Na atoms are situated within the rings and mobile Na atoms between the columns. The size of the channels is dictated by the size of the M06 octahedra. Na5GdSi4012 and Na5-zGd1_xZrxSi4012, which can be sintered to 95% theoretical density and appear to be resistant to attack by Na, are probably the most practical materials for use as a solid electrolyte.
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