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ELECTRONIC TRANSPORT IN MOLYBDENUM-SESQUISULFIDE
Abstract
This dissertation presents the results of detailed investigations of the conductivity, thermoelectric power, and conductivity fluctuations in Mo(,2)S(,3). In particular, a very unusual time-dependent conductivity is observed. Single crystals of Mo(,2)S(,3) exist as long, needle-shaped fibers which have a metallic appearance. At room temperature, the crystal structure is monoclinic, with zig-zag molybdenum chains which run parallel to the crystalline b-axis. The electrical resistivity of Mo(,2)S(,3) shows the existence of two first-order phase transitions at 182 K and 145 K on cooling. In addition, a large peak in the resistivity is observed at 80 K. Below 80 K, the resistivity is metal-like, decreasing with decreasing temperature. The time-dependent conductivity measurements were made at temperatures between 75 K and 300 K first by heating the Mo(,2)S(,3) sample a few degrees and then rapidly quenching (in a few milliseconds). For temperatures below 110 K, the sample conductivity was observed to slowly decrease after thermal quenching, with a characteristic time constant varying between 10 mS (110 K) and several minutes (75 K). These results show that a relatively high conductivity metastable state exists for the charge carriers. All of the time-dependent conductivity measurements can be explained by a double-well potential model for the carriers. The conductivity fluctuations (electrical noise) were measured by passing a constant electric current through the sample, and measuring the electrical noise thereby generated. The frequency dependence of the noise is completely consistent with the double-well potential model used to describe the time-dependent conductivity measurements. The thermoelectric power measurements show that the dominant charge carriers in Mo(,2)S(,3) are holes. The time-dependent thermoelectric power measurements show a behavior similar to the time-dependent conductivity. Two physical models for the charge carriers in Mo(,2)S(,3) appear most likely to be able to explain these experimental results. Both a charge-density wave model, and an acoustic polaron model are discussed at some length, and further investigations to help determine which, if either, of these models is correct are suggested.
Subject Area
Condensation
Recommended Citation
FAGERQUIST, RANDY LEE, "ELECTRONIC TRANSPORT IN MOLYBDENUM-SESQUISULFIDE" (1985). ETD collection for University of Nebraska-Lincoln. AAI8526590.
https://digitalcommons.unl.edu/dissertations/AAI8526590