engleski

Resistivity anomalies above 90K in ceramic Na_xWO_(3-delta)

Na_xWO_3 has been found to exhibit anomalies in the region of 90-120 K, which were recently attributed by Reich and Tsabba (Eur.Phys.J.B 9,1 (1999)) to possible high-temperature surface superconductivity with T_c = 91 K. We report on the synthesis, microstructure, SQUID magnetization and transport measurements of ceramic Na_xWO_(3-delta). We conclude that the intrinsic behavior of the material appears to be activated above 100 K. Below 100 K, there are anomalies which are observed, but may be related to dielectric breakdown. The possible origins of this anomalous behavior are discussed in terms of possible percolative superconductivity or charge-density wave formation.

high T_c surface superconductivity; ceramic superconductors; percolative superconductivity

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