Revision of the high Poisson ratio phenomenon in copper prior to shock melting
Phys. Rev. B 113, 094110 – Published 17 March, 2026
DOI: https://doi.org/10.1103/2r3z-q8cv
Abstract
High Poisson's ratio phenomenon in copper prior to shock melting has been observed and attributed to partial melting, due to its presumed simple solid structural phase diagram including only the face-centered cubic (fcc) phase. Recent shock-compression experiments indicate a possible transition to the body-centered cubic (bcc) structure under high pressure and temperature. Determination of the fcc-bcc phase boundary is essential for assessing copper's effectiveness as a pressure standard, and the fcc-bcc transition also provides an alternative mechanism for the high Poisson's ratio phenomenon. This study uses first-principles density functional theory to calculate the phase boundary by comparing the Gibbs free energies of the two phases. The derived phase boundary extends from approximately 80 GPa and 3400 K to over 1.2 TPa and 9000 K, consistent with prior experimental findings. Elastic properties of copper across the fcc-bcc phase boundary obtained from ab initio molecular dynamics simulations confirm that the decrease in the shear modulus and the increase in Poisson's ratio are due to the fcc-bcc transition rather than partial melting.
