| Abstract Scope |
The thermal stability of high entropy alloys is often attributed to their high configurational entropy, which increases with the addition of more elements. However, the impact of these additions on vibrational and electronic entropy has received little attention. Using a PPMS from Quantum Design, we measured S_vib,el in AlₓCoCrFeNi, AlₓMn₀.₇₅CoCrFeNi, AlₓNbTa₀.₅TiZr, and their Al-free variants. Al additions often reduce vibrational entropy—for instance, at T = 385 K, ΔS_vib,el = −0.43 kB/atom in Al₀.₇₆CoCrFeNi (vs. theoretical ΔS_config = +0.22 kB/atom) and −0.31 kB/atom in Al₀.₂₉NbTa₀.₅TiZr (vs. ΔS_config = +0.17 kB/atom). We attribute this reduction to stiff Al bonding in transition metal systems and to Al’s low relative mass in refractory systems. We are also investigating how chemical ordering alters the configurational entropy and the vibrational entropy in these alloys. Supported by AFOSR award FA9550-25-1-0093. |