Electrical resistivity of solid and liquid iron at high pressure in large-volume presses: A critical comparison between powder-compacted and solid wire samples

An accurate measurement of electrical resistivity of iron (Fe) and Fe-alloy systems at high temperatures and high pressures is essential for understanding the dynamics inside the metallic cores of planetary bodies. Many experimental studies have been carried out on the electrical resistivity of Fe and Fe-alloy compositions using both powder samples and wire samples with different experimental designs, and discrepancies in the measured values still persist. In this study, we evaluated multiple experimental designs using the four-wire method with Fe powder samples to assess the influence of sample geometry, melting, and contact materials on measured resistivity values in a large-volume multi-anvil press. Three configurations with varying sample diameters and geometrical constraints were tested at 5 GPa and beyond the melting temperature of Fe, revealing significant uncertainties due to deformation, especially in the molten state. These results indicate that electrical resistivity measurements with powder samples should be taken as the upper bound unless sample geometry is well preserved. Further experiments examined the effect of disk materials (Pt, W, and Re), with results indicating that higher resistivity materials, such as Re, may introduce larger discrepancies in measured values. With a geometric correction derived from previous room-temperature resistivity data, the agreement of resistivity values between wire and powder samples improves significantly. A two-step approach was then suggested for future experiments with powder samples to reduce uncertainties in resistivity measurements.