Dominant influence of vibrational entropy on the phase transition in CoNi and related high-entropy alloys

This is the authors' abstract. We don't add key points for this paper.

Entropy is an effective means to stabilize the high-temperature phase of a material. However, the origin of entropy is diverse, including configurational, vibrational, electronic, and magnetic, amongst others. It is still unclear, and sometimes controversial, which type of entropy plays a dominant role in a phase transition. Here, the individual entropy contributions during a hexagonal-close-packed (hcp) to face-centered-cubic (fcc) phase transition were quantified in transition metal based random solid solution alloys. We show, by inelastic neutron scattering measurements, that the vibrational entropy accounts for ∼80% of the overall entropy change in a C⁢o75⁢N⁢i25 binary alloy, whereas the contributions from electronic and magnetic entropy are small. First-principles calculations further identified that the excess vibrational entropy stems from the disappearance of optical phonon modes in the hcp phase. Analysis of a multicomponent C⁢r20⁢M⁢n20⁢F⁡e20⁢C⁢o40 high-entropy alloy leads to the same conclusion, confirming the essential role of the vibrational entropy in driving the hcp-to-fcc phase transition in these alloys.