Discovery of Elusive K₄ O₆ , a Compound Stabilized by Configurational Entropy of Polarons

Synthesis of elusive K₄ O₆ has disclosed implications of crucial relevance for new solid materials discovery. K₄ O₆ forms in equilibrium from K₂ O₂ and KO₂ , in an all-solid state, endothermic reaction at elevated temperature, undergoing back reaction upon cooling to ambient conditions. This tells that the compound is stabilized by entropy alone. Analyzing possible entropic contributions reveals that the configurational entropy of "localized" electrons, i.e., of polaronic quasi-particles, provides the essential contribution to the stabilization. We corroborate this assumption by measuring the relevant heats of transformation and tracking the origin of entropy of formation computationally. These findings challenge current experimental and computational approaches towards exploring chemical systems for new materials by searching the potential energy landscape: one would fail in detecting candidates that are crucially stabilized by the configurational entropy of localized polarons.