Electrical resistivity anomaly in quasi-one-dimensional compound KFeS₂

The origin of an anomalous behavior of DC resistivity in a quasi-one-dimensional compound KFeS₂ was studied using transmission-electron-microscopy (TEM) and differential scanning calorimetry (DSC). The resistivity of the as-grown crystal exhibits sharp decrease around room temperature with a thermal hysteresis. However, this sharp decrease in the resistivity disappears after annealing the specimen at 300°C for two days. A endothermic peak in DSC is found in the range of 230K-280K, which corresponds to that of the decrease in the resistivity. TEM images of as-grown specimens show larger numbers of dislocations and higher density of plain defects comparing with annealed specimens. The FeS₂ chain is supposed to be interrupted and to form "FeS₂ segment". A model based on some kind of defects relaxes to thermal equilibrium state is proposed.