A flash heating method for measuring thermal conductivity at high pressure and temperature: Application to Pt

•Novel technique for measuring thermal conductivity at high pressure and temperature outlined.•Thermal Conductivity measurements on platinum at 35–55 GPa and up to 2300 K reported.•Empirical model for electrical and thermal conductivity in platinum under pressure and temperature presented.•Platinum is found to follow Stacey’s prediction of constant resistivity at melting in simple metals.•Use of Stacey’s law in application to planetary cores is justified.

The transport properties of matter at high pressure and temperature are critical components in planetary interior models, yet are challenging to measure or predict at relevant conditions. Using a novel flash-heating method for in-situ high-temperature and high-pressure thermal conductivity measurement, we study the transport properties of platinum to 55 GPa and 2300 K. Experimental data reveal a simple high-pressure and high-temperature behavior of the thermal conductivity that is linearly dependent on both pressure and temperature. The corresponding electrical resistivity evaluated through the Wiedemann–Franz–Lorenz law is nearly constant along the melting curve, experimentally confirming the prediction of Stacey for an ideal metal. This study together with prior first-principles predictions of transport properties in Al and Fe at extreme conditions suggests a broad applicability of Stacey’s law to diverse metals, supporting a limit on the thermal conductivity of iron at the conditions of Earth’s outer core of 90 W/mK or less.