Ultrawide Temperature Range Super-Invar Behavior of R2(Fe,Co)17 Materials (R = Rare Earth)

Super Invar (SIV), i.e., zero thermal expansion of metallic materials underpinned by magnetic ordering, is of great practical merit for a wide range of high precision engineering. However, the relatively narrow temperature window of SIV in most materials restricts its potential applications in many critical fields. Here, we demonstrate the controlled design of thermal expansion in a family of R-2(Fe, Co)(17) materials (R = rare Earth). We find that adjusting the Fe-Co content tunes the thermal expansion behavior and its optimization leads to a record-wide SIV with good cyclic stability from 3-461 K, almost twice the range of currently known SIV. In situ neutron diffraction, Mossbauer spectra and first-principles calculations reveal the 3d bonding state transition of the Fe-sublattice favors extra lattice stress upon magnetic ordering. On the other hand, Co content induces a dramatic enhancement of the internal molecular field, which can be manipulated to achieve ultrawide SIV over broad temperature, composition and magnetic field windows. These findings pave the way for exploiting thermal-expansion-control engineering and related functional materials.

Automated summary

By adjusting the Fe-Co content, researchers have optimized the thermal expansion behavior in a family of R-2(Fe, Co)(17) materials, achieving a record-wide SIV range with good cyclic stability. This breakthrough paves the way for exploiting thermal-expansion-control engineering and related functional materials.