The temperature dependence of resistivity and thermoelectric power in lanthanum molybdenum oxide crystal La₂Mo₂O₇

Electrical resistivity, voltage - current (V-I) characteristics and thermoelectric power (TEP) at various temperatures in the quasi-two-dimensional single crystal La₂Mo₂U₇ were measured. It was found that at 130 K the resistivity shows a metal - semiconductor transition, and the TEP has a minimum value. In the semiconducting states below 130 K, the electronic transport presents a clear non-linear behaviour. By analysis of the above data, it is indicated that above 130 K the crystal is a metal and electrons are dominant carriers; below 130 K the crystal becomes a semiconductor with a small energy gap, the two types of carrier being possibly coexistent. The anomalies of TEP and resistivity near 130 K may be associated with the formation of so-called charge-density waves due to the partial opening of a gap.