FIRST OBSERVATION OF WEAK LOCALIZATION EFFECTS IN ORGANIC CONDUCTORS ?

We have studied the transverse magnetoresistance of the organic series (DMtTSF)2 X down to 2 K and up to 40 T. Under about 20 K and 8 T a negative magnetoresistance appears only for salts whose X is a tetrahedral anion. This new phenomenon is interpreted as a two-dimensional (2D) weak localization effect

Optimization of high strength materials : Design of the engineering parameters through the nanostructure characterization

High strength and high conductivity conductors are elaborated via strong plastic deformation by drawing, for the winding of high pulsed magnetic field coils. These nanocomposites are composed of a copper matrix containing 9.106 continuous niobium nanofilaments. The microstructure has been studied in detail using X-Ray diffraction, TEM, HREM : the niobium fibers are nanowhiskers separated from the inter-filamentary copper by semi-coherent interfaces. TEM in-situ tensile tests revealed a mechanism of single dislocation loops nucleation in the nanoscaled copper matrix. Its analytical simulation takes into account all the characteristics of the structure and is in good agreement with the experimental strength data. All these fundamental studies are combined to define the engineering parameters for the strength optimization of the nanocomposites. These parameters were applied to design the new nanocomposites. The first strength results are given for conductors containing 52.106 filaments with a diameter down to 25 nm