Designer Entropy Enables Negative and Zero Thermal Expansion beyond 1000 K
Negative thermal expansion (NTE) and zero thermal expansion (ZTE) materials are technologically relevant for precision engineering, yet their practical deployment is constrained by narrow operating temperature windows. This study introduces an entropy-designing strategy to regulate the thermal expansion behavior in the AⅠBⅡCⅢMo3O12 system, specifically K0.4(Mg0.25Mn0.25Co0.25Ni0.25)0.4Sc1.6Mo3O12 (CE0.4MO) and related CExMO compositions (x = 0.4, 0.6, 0.8, 1.0). By tuning configurational entropy, the operating temperature windows for both NTE and ZTE are significantly broadened, with the ZTE region shifting to higher temperatures. Among single-phase compositions, CE0.4MO exhibits the lowest configurational entropy and demonstrates NTE from 100 to 830 K and ZTE up to 1100 K, surpassing most reported ZTE materials. Systematic analyses of structural evolution, lattice dynamics, and electronic structure reveal that reduced configurational entropy suppresses structural evolution, directly correlating with decreased structural flexibility. Higher atomic displacement parameters (ADPs) of oxygen in CE1.0MO provide experimental evidence for enhanced flexibility. Raman spectroscopy shows that the full width at half maximum (FWHM) of peaks in the 750–900 cm-1 range positively correlates with configurational entropy, indicating reduced lattice disorder, while modes within 750–1050 cm-1 blue-shift as entropy decreases, confirming lattice stiffening. Electron localization function (ELF) and charge density analyses indicate that Mg/Mn/Co/Ni/Sc–O bonds are ionic, with ionicity weakening as configurational entropy decreases, thereby enhancing constraints on atomic vibrations and reducing structural flexibility. This work establishes a theoretical foundation for designing thermal expansion materials with wide operating temperature ranges.