Method for the determination of the specific heat of metals at low temperatures under high pressures

Efforts are made to determine the absolute specific heat of metals as a function of pressure with an accuracy, which, for the first time, will permit a direct evaluation of the pressure variation of the electronic and phonon parameters gamma and vartheta(D'), respectively. This is achieved by employing the ac method of Sullivan and Seidel, and choosing a suitable sample configuration within a piston-cylinder pressure cell. Essential is the use of diamond powder as a pressure transmitting medium, which because of its low heat capacity and high thermal resistance, couples the sample loosely to the temperature bath, represented by the pressure cylinder. Thus, the thermal requirements of the ac method are met, and corrections--if necessary--are fully tractable. High sensitivity even at the lowest temperatures is obtained by the use of thin slices, prepared from standard carbon resistors, for thermometers. Although delicate, these sensors withstand pressures of more than 20 kbars and remain sensitive. A thorough comparison of results on indium with the literature data at zero pressure is undertaken. It shows that the accuracy of the present results is comparable with that from literature data. Preliminary results at pressures up to 8 kbar are shown; they will be discussed in a separate paper.