Giant negative thermal expansion in Ge-doped anti-perovskite manganese nitrides

We report the discovery of a large negative thermal expansion (NTE) up to α=−25×10−6K−1 (α: coefficient of linear thermal expansion) in Ge-doped anti-perovskite manganese nitrides Mn3AN (A=Cu,Zn,Ga). This gigantic NTE is several to ten times higher than that of commercially available NTE materials. The discontinuous lattice expansion seen in pure Mn3AN is broadened by Ge substitution over a wide temperature window, at widest ΔT∼100K, around room temperature. Such a large, isotropic and nonhysteretic NTE is desirable for practical applications.