A Technique for Measurement of the Heat Capacity of Metals under Pressure

A method is described that can be used for the determination of the heat capacity of a metal (or a semiconductor) as a function of pressure and temperature. The method involves use of a dc electric pulse. If a constant current I is passed through a wire sample of resistance R, the heat capacity C_p is related to the increase in temperature by the expression $$C_p{\mathrm{=I}}^3{\mathrm{RR\prime /(dE/dt)}}_{\text{t=0}}$$ , where R′ is the temperature derivative of the resistance, and (dE/dt)_t=0 is the limiting value of the time rate of change of the emf across the sample. Data are given for iron to 100 kilobars in the temperature interval from 77 to 300 K. The results obtained are in accord with earlier theoretical estimates. The Curie temperature T_c of gadolinium has also been determined from heat capacity measurements; its rate of change with pressure was found to be dT_c/dP=−1.3 K/kilobar. With the equipment that is available at the present time, the measurements can be made as long as the specific resistance is 5 μΩ·cm or greater.