Resistive anomalies at near 250 K in Hg-Ca-Cu-O and Fe-S systems

High pressure synthesized samples of nominal composition of Ca2-xHgxCuOy wi th x = 0.10 similar to 0.20 under reductive synthesis condition showed stab le and reproducible resistivity onset transition at 225 similar to 254 K ac companied by rapid drop of thermoelectric power without accompanying magnet ic susceptibility transition. Fe1-xS (x = 0) by mechanical alloying method showed resistivity anomaly and thermal hysteresis at 150 similar to 180 K. These resistive anomalies may be phase transition of unknown origin rather than an indication of superconductivity.