Isotropic Zero Thermal Expansion in (Sc_0.85Al_0.1Cr_0.05)F₃

Zero thermal expansion, also known as the Invar effect, has great application potential in the field of precision equipment. In this work, a zero thermal expansion material of (Sc_0.85Al_0.1Cr_0.05)F₃ (α_l = -0.83 × 10^-6 K^-1, 173-473 K) was prepared by the solid-state reaction method. A joint study combining variable-temperature X-ray diffraction, pair distribution function, and density functional theory was conducted to elucidate the thermal expansion mechanism. The introduction of Al and Cr leads to local structural distortions, altering the vibrational modes of fluorine atoms and weakening their contribution to negative thermal expansion. Density functional theory calculations further confirm that the weighted sum of the total Grüneisen parameter is close to zero, consistent with the zero thermal expansion characteristics. This study not only provides a new zero thermal expansion material but also reveals the intrinsic relationship between material structure and thermal expansion properties.