Non?Isotropic Contraction and Expansion of Samples in Diamond Anvil Cells: Implications for Thermal Conductivity at the Core?Mantle Boundary

The thermal conductivities of mantle and core materials have a major impact on planetary evolution, but their experimental determination requires precise knowledge sample thickness at high pressure. Despite its importance, in most diamond anvil cell (DAC) experiments is not measured inferred from equations state, assuming isotropic contraction upon compression or expansion decompression. Here we provide evidence that DAC both assumptions are invalid for range mechanically diverse (KCl, NaCl, Ar, MgO, silica glass, Al2O3). Upon compression, these samples ?30–50% thinner than expected contraction. Most surprisingly, all the studied continue to thin decompression 10–20 GPa. Our results partially explain some discrepancies among highly controversial conductivity values iron Earth's conditions. More generally, suggest situ characterization geometry essential measurements