Thermal conductivity measurement under hydrostatic pressure using the 3ω method

We have designed and modeled new techniques, based on the 3omega method, to measure thermal conductivity of liquids (kappa(l)) and solids (kappa(s)) under hydrostatic pressure (P). The system involves a solid sample immersed in a liquid pressure medium, both of which have unknown thermal properties. The temperature (T) and P dependance of kappa(l) are first determined through the use of a modified 3omega technique. This method uses a conducting wire (Pt, in this work), which is immersed in the pressure medium, as the heater/sensor. In addition to kappa(l), this allows for the accurate determination of the specific heat per volume of the liquid and Pt, (rhoC)(l) and (rhoC)(Pt), respectively. The information of kappa(l) and (rhoC)(l) can then be used to make corrections to measurements of kappa(s), in which the sample is immersed in the pressure medium, and a metal strip acts as the heater/sensor. We present the T and P dependence of kappa(l) and (rhoC)(l) for the widely used pressure medium 3M Fluorinert FC77 up to 0.8 GPa. The measurement of kappa(s) for a thermoelectric clathrate material, Sr8Ga16Ge30, in FC77 is analyzed in detail, and the refined data achieves an accuracy of 1%. The setup can be modified to measure kappa and rhoC up to 3.5 GPa. (C) 2004 American Institute of Physics.