Electrical Resistivity of Cu and Au at High Pressure above 5 GPa: Implications for the Constant Electrical Resistivity Theory along the Melting Curve of the Simple Metals.

The electrical resistivity of solid and liquid Cu and Au were measured at high pressures from 6 up to 12 GPa and temperatures ∼150 K above melting. The resistivity of the metals was also measured as a function of pressure at room temperature. Their resistivity decreased and increased with increasing pressure and temperature, respectively. With increasing pressure at room temperature, we observed a sharp reduction in the magnitude of resistivity at ∼4 GPa in both metals. In comparison with 1 atm data and relatively lower pressure data from previous studies, our measured temperature-dependent resistivity in the solid and liquid states show a similar trend. The observed melting temperatures at various fixed pressure are in reasonable agreement with previous experimental and theoretical studies. Along the melting curve, the present study found the resistivity to be constant within the range of our investigated pressure (6-12 GPa) in agreement with the theoretical prediction. Our results indicate that the invariant resistivity theory could apply to the simple metals but at higher pressure above 5 GPa. These results were discussed in terms of the saturation of the dominant nuclear screening effect caused by the increasing difference in energy level between the Fermi level and the d-band with increasing pressure.

Technique, cell assembly, and measurement of T-dependent electrical resistivity of liquid Fe devoid of contamination at P, T conditions.

Since the cores of rocky planetary bodies are mainly Fe in composition, the understanding of the electrical resistivity and thermal conductivity of solid and molten Fe at pressure and temperature conditions is vital in placing a constraint on the quantity of heat flux from the cores of these planets. We develop an experimental technique and cell design to measure the temperature-dependent electrical resistivity of solid and molten Fe and other transition metals under high pressure. This addresses the problem of metal sample contamination encountered in designs that used W/Re, W, and Mo in direct contact with the sample. At first, we attempted to improve these pre-existing designs by testing the suitability of Hf and Zr metals to serve as a mechanical barrier between the electrodes and the sample. Unfortunately, our result shows that solid Hf and Zr dissolve in molten Fe and are not suitable for this purpose. Next, we adopt the same sample material, Fe, for electrodes and leads while the thermocouple leads are taken through the gasket and protected against frequent mechanical breakage using the shielding technique. The recovered Fe samples compressed at various pressure conditions and heated up to 200 K above the melting temperature show no trace of contamination. As anticipated, the resistivity increases and decreases with increasing temperature and pressure, respectively. Thus, to closely measure the electrical resistivity of molten Fe and other similar metals at extreme conditions, it is necessary to ensure liquid containment, eliminate biased voltage through the current reversal technique, and ensure the use of the same material for the electrode and sample while monitoring the sample temperature using a thermocouple placed close to but not in contact with the sample. Our developed technique provides the highly demanding technique for investigating the temperature-dependent electrical resistivity of Fe and other similar metals devoid of contamination at extreme conditions. This progress will accelerate studies which will provide a detailed understanding of the electrical and heat transport properties of Fe as it applies to the core of rocky planetary bodies.