The effect of high pressure on the thermoelectric power and resistance of aluminum and gold

Abstract

The effect of pressure up to 4 kbar on the thermoelectric power of aluminum, gold, nickel and platinum has been determined. The change in resistance with pressure of aluminum and gold has also been measured. Measurements were carried out at temperatures between room temperature and 1300 oK or, in the case of aluminum, o between room temperature and 900 K. A null method was used for the resistance measurements and for the thermoelectric power measurements, requiring an externallyheated pressure vessel. The use of a special molybdenum alloy made this possible. The high temperature thermoelectric power data for aluminum are separated into terms associated with three thermally activated defects: the monovacancy, the divacancy, and the impurityvacancy pair. Values for the formation energy and the volume are obtained for each of these defects. The effect of vacancies in gold is dominated by the effect of pressure on the lattice so that no quantitative results can be determined. An effect consistent with a monovacancy model is detected. Measurements in platinum and nickel were carried out to test the sensitivity of the method to changes in scattering mechanism. A phenomenological model is presented to explain the resistance data in aluminum and gold. This model gives the accepted formation volume for monovacancies in gold. It gives a value for the formation volume of monovacancies in aluminum in agreement with the value obtained from the thermoelectric power measurements. The presence of divacancies in aluminum is strongly supported by this mode 1.