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This paper introduces a quantum spectral thermodynamic framework that links phonon spectral broadening to free energy, coupled with an uncertainty-guided active learning approach, to explore 7.7 million high-entropy ceramic configurations at DFT fidelity. The key result is the discovery that phonon self-energy effects from chemical disorder intrinsically stabilize phases by compensating unfavorable mixing enthalpies, revealing a ~12 at.% solute threshold for mechanical properties and enabling unusual high-temperature stiffness with low thermal conductivity. This work establishes a quantum spectral foundation for understanding many-body interactions and thermodynamics in solids, while providing a scalable method for exploring vast multicomponent chemical spaces.
Chemical disorder in high-entropy ceramics intrinsically stabilizes phases beyond configurational entropy, driven by phonon self-energy effects, and unlocks a unique combination of high-temperature stiffness and low thermal conductivity.
Understanding phase stability and navigating vast compositional spaces in multicomponent solids remain central challenges in solid-state chemistry. Here, we develop a quantum spectral thermodynamic framework connecting interaction-induced phonon spectral broadening to free energy, alongside an uncertainty-guided active-learning workflow that explores 7.7 million high-entropy ceramic configurations at density-functional-theory fidelity, achieving a $10^5$-fold acceleration. We show that phonon self-energy effects arising from chemical disorder provide an intrinsic vibrational contribution to thermodynamic stabilization beyond ideal configurational entropy, compensating unfavorable mixing enthalpies and suppressing phase separation. Across the chemical space, we uncover a robust ~12 at.% solute threshold separating strengthening and softening regimes, associated with the filling of metal-carbon antibonding states. Chemical disorder further enables an unusual combination of high-temperature mechanical stiffness and low thermal conductivity, together with anomalous temperature-dependent lattice heat transport. This work establishes a quantum spectral foundation for connecting many-body interactions to thermodynamics and phase stability, while providing a scalable framework for exploring previously inaccessible multicomponent chemical spaces.
