Giant negative thermal expansion in Fe-doped layered ruthenate ceramics

The effects of iron doping on the giant negative thermal expansion (NTE) of Ca₂RuO_{4- y} ceramics are investigated. Fe-doped ruthenate ceramics exhibit a large NTE even though the crystallographic unit-cell volume shows no NTE. The anisotropic thermal strain of crystal grains consumes open spaces in the sintered body and causes giant bulk volume contraction on heating. This giant NTE is reproducible against repeated thermal cycling, indicating a tough microstructure. The thermal expansion of epoxy resin is fully suppressed below 400 K by the 56 vol % loading of the Fe-doped ruthenate ceramic powder, demonstrating tough microstructures and the capability of thermal expansion compensation of the ruthenate sintered body.