Metastable Conduction States in Mo\u3csub\u3e2\u3c/sub\u3eS\u3csub\u3e3\u3c/sub\u3e: Pulse Conductivity and Thermoelectric Power

Mo2S3 is a linear-chain-structure compound which has two inequivalent zig-zag Mo chains parallel to the b axis. It undergoes at least two phase transitions below room temperature (at 182 and 145 K upon cooling). X-ray-diffraction measurements show that both incommensurate and commensurate structural distortions are associated with the phase transitions. We repot here the results of electrical-conductivity and thermoelectric-power measurements on Mo2S3 . By using pulsed electric currents to rapidly heat and cool the sample while electrical-resistivity or thermoelectric-power measurement are being made, we are able to show that below the lower-temperature phase transition, the carriers in Mo2S3 can be either in a poorly conducting ground state or in a relatively highly conducting metastable state. The lifetime of a carrier in the metastable state is strongly dependent on the temperature and is more than 200 s at 77 K. The temperature dependence of the conductivity and all of the pulse conductivity measurements are consistent wit ha phenomenological double-well-potential model for the carrier in Mo2S3. Three possible models which can give rise to such a double-well potential are discussed: (1) a defect-trapping model, (2) an acoustic-polaron model, and (3) a charge-density-wave mode