RESISTIVE ANOMALIES AT NEAR 250 K IN Hg-Ca-Cu-O AND Fe-S SYSTEMS

Abstract

High pressure synthesized samples of nominal composition of Ca2-xHgajCuO-y with x = 0.10 »J 0.20 under reductive synthesis condition showed stable and reproducible resistivity onset transition at 225 ~ 254 K accompanied by rapid drop of thermoelectric power without accompanying magnetic susceptibility transition. Fei-xS (x=0) by mechanical alloying method showed resistivity anomaly and thermal hysteresis at 150 <~ 180 K. These resistive anomalies may be phase transition of unknown origin rather than an indication of superconductivity.