Isotropic Zero Thermal Expansion in Yb(Al,Mn)₂: Achieving Continuous Shiftability over a Wide Temperature Range

Zero thermal expansion (ZTE) substances, whose volume remains invariant under temperature variations, have attracted significant attention owing to their extensive potential applications in advanced technology fields. However, practical challenges persist, including thermal expansion anisotropy, ferromagnetism, high density, and restricted ZTE temperature windows. In this study, we have achieved a lightweight, nonferromagnetic, isotropic ZTE in Yb(Al,Mn)₂ alloys, which exhibits continuous shiftability of the ZTE temperature window across a wide range (140-650 K). By employing multiple advanced experimental techniques and combining first-principles calculations, we have elucidated that the ZTE behavior originates from valence fluctuations accompanied by local structural distortions. The latter manifests as the first two observed effects: the splitting of local bond lengths and the attenuation of atomic displacements. More importantly, the induced enhancement of hybridization between Mn-3<i>d</i> and Yb-4<i>f</i> orbitals is identified as the primary mechanism responsible for the emergence of shiftability over a wide temperature range. This work presents an unprecedented phenomenon of continuously shiftable ZTE temperature windows observed in the mixed-valence system Yb(Al,Mn)₂, which holds significant potential for diverse thermal expansion control applications in advanced technological fields, paving the way for next-generation devices requiring exceptional dimensional stability. Furthermore, the modulation of valence fluctuations provides new strategies for the development of new ZTE materials in the future.