Nature © Macmillan Publishers Ltd 19988 letters to nature 456 NATURE | VOL 394 | 30 JULY 1998 amount to Ϯ10%, this would result in a total T c variation of 7 K in the bulk phase diagram. In strained films a total variation of ϳ40 K is observed, together with a drastic change in T ‫ء‬ . Hence, the lattice deformations associated with the strain fundamentally modify the energy scales, leading to the formation and condensation of the superconducting pairs. As the pair formation strongly influences the spin and charge excitation spectrum of the normal state, r(T) and the metal-insulator transition are also considerably modified. Further work to identify and quantify the subtle lattice deformations responsible for these changes needs to be done. In any case, the data reported here emphasize that T c increases as the distance between consecutive CuO 2 planes increases, in contradiction of a recent theoretical prediction 30 . Our data also show that adjustment of the epitaxial strain offers a unique way to increase T c and to reveal the fundamental role played by the interlayer coupling. Ⅺ

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The physical and chemical properties of a new class of lithium conducting polymer electrolytes formed by dispersing ceramic powders at the nanoscale particle size into a poly(ethylenoxide) (PEO)-lithium salt, LiX complexes, are reported and discussed. These true solid-state PEO-LiX nanocomposite polymer electrolytes have in the 30-80 °C range an excellent mechanical stability (due to the network of the ceramic fillers into the polymer bulk) and high ionic conductivity (promoted by the high surface area of the dispersed fillers). These important and unique properties are accompanied by a wide electrochemical stability and by a good compatibility with the lithium electrode (assured by the absence of any liquids and by the interfacial stabilizing action of the dispersed filler), all this making these nanocomposite electrolytes of definite interest for the development of advanced rechargeable lithium batteries.

The addition of nanometric fillers (e.g., SiO2 , TiO2 ) to Pfalse(EO)nLiClO4 polymer electrolytes induces consistent improvement in the transport properties. The increase in conductivity and in the cation transference number is attributed to the enhancement of the degree of the amorphous phase in the polymer matrix, as well as to some acid‐base Lewis type, ceramic‐electrolyte interactions. This model is confirmed by results obtained from a detailed impedance spectroscopy study carried out on poly(ethylene oxide) [P(EO)]‐based polymer electrolyte samples with and without ceramic fillers. © 2000 The Electrochemical Society. All rights reserved.

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