Experimental Investigations of the Thermodynamics and Pinning in the Charge-Density Wave System Potassium- Molybdate

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This research is concerned with unresolved fundamental problems associated with the charge-density-wave (CDW) transition, namely the nature and effects of fluctuations in the neighborhood of the CDW transition and secondly the nature of the very weak impurity interactions with the CDW. The role of phonon entropy on the thermodynamics of the CDW transition will be studied. Improved specific heat, elastic, and magnetization measurements will permit a more careful confirmation of scaling laws. A novel resonant ultrasonic method will be used for simultaneous evaluation of all components of the elastic modulus tensor as a function of temperature. Presently, thermodynamic measurements do not yet confirm the criticality temperature range shown by x-ray diffraction. Susceptibility measurements will be attempted to further explore the validity of the scaling laws. It is hoped to provide experimental evidence on the influence of fluctuations on charge and heat transport and to compare these results with thermodynamic quantities. A second portion of the research is concerned with the synthesis of patassium molybdate with isotopic substitution on the oxygen (0) site with the obtainment of well controlled ratios of 180/160 or 170/160. Both transport and nuclear magnetic resonance measurements will be undertaken to obtain evidence on the pinning of the CDW. A search for the effects of the isotopic substitution on the CDW phase transition will be made. This will be the first attempt to explore isotopic effects on CDW systems.