Electronic-Entropy-Driven Solid-Solid Phase Transitions in Elemental Metals

TL;DR

This study uses finite-temperature density functional theory to map the phase diagram of seventeen elemental metals, revealing electronic entropy-driven solid-solid phase transitions across different crystal structures.

Contribution

It demonstrates that electronic entropy can induce solid-solid phase transitions in metals, a factor previously underappreciated in structural stability analyses.

Findings

All studied metals, except Mg and Pb, undergo electronic entropy-driven phase transitions.

Transition electronic temperatures are identified from free-energy crossings.

Electronic entropy is shown to be a key factor in metallic structural stability under excitation.

Abstract

We compute the thermodynamic phase diagram of seventeen elemental metals with hexagonal close-packed (hcp), face-centered cubic (fcc), and body-centered cubic (bcc) crystal structures using finite-temperature density functional theory. Helmholtz free-energy differences between competing hcp, fcc, and bcc phases are evaluated as functions of electronic temperature up to 7 eV, allowing us to identify solid-solid phase transitions driven by electronic entropy. The systems studied include Zr, Ti, Cd, Zn, Co, and Mg (hcp), Ni, Cu, Ag, Al, Pt, and Pb (fcc), and Cr, W, V, Nb, and Mo (bcc) in their ground-state structures. From the free-energy crossings, we extract the transition electronic temperatures and analyze systematic trends across the metallic systems. We found that all the studied systems go through one or two solid-solid phase transition caused purely by electronic entropy except Mg and Pb. Our results establish electronic entropy as a key factor governing structural stability in metals under strong electronic excitation.