The Pressure Coefficient of Thermal Conductivity of Metals

The pressure coefficients of thermal conductivity of copper, silver, and gold were determined by means of an improved longitudinal heat flow method. The results indicate that the ratio of the thermal to the electrical conductivity (the Wiedemann-Franz ratio) for these metals, over a pressure range of 12,000 kg/${\mathrm{cm}}^2$, has a small positive coefficient of approximately 1 percent in 10,000 kg/${\mathrm{cm}}^2$. These results are at variance with those of Bridgman who used a similar method but found that the pressure coefficient of the Wiedemann-Franz ratio may be either negative or positive and is more often negative. Experiments are reported which prove that the negative coefficients found by Bridgman were due to a systematic convection error undiscovered in his longitudinal heat flow method. It is reasonable to suppose that the positive pressure coefficient of the Wiedemann-Franz ratio is due to the nonelectronic part of the thermal conductivity, and this assumption is further supported by the correlation between these positive coefficients and the volume compressibilities of the metals.