Axis thermal expansion switching in transition-metal zirconides TrZr₂ by tuning the c/a ratio

This study examines the temperature-dependent evolution of the lattice constants for various CuAl2-type compounds, including NiZr2, (Co,Rh,Ir)Zr2, (Fe,Co,Rh,Ir)Zr2, and (Co,Ni,Cu,Rh,Ir)Zr2, in the pursuit of negative or zero thermal expansion. Results reveal that NiZr2 has positive thermal expansion, while the other compounds exhibit uniaxial negative thermal expansion along the c-axis contraction. The study suggests that the c-axis thermal expansion can be controlled by manipulating the c/a ratio through Tr-site substitution, providing a design principle for achieving negative thermal expansion of the c-axis and potentially zero thermal expansion in a single compound in TrZr2 compounds.