Low-temperature negative thermal expansion of the antiperovskite manganese nitride Mn3CuN codoped with Ge and Si

We have synthesized antiperovskite manganese nitrides Mn3(Cu0.6SixGe0.4−x)N, (x=0–0.2) and investigated their negative thermal expansion (NTE) in the temperature range of 80–300 K. We found that the transition temperature of NTE moves toward lower temperature region and as well the NTE operation-temperature window (ΔT) becomes broader with increasing Si content. Typically, the giant low-temperature NTE coefficient identified in Mn3(Cu0.6Si0.15Ge0.25)N reaches as large as −16×10−6 K−1, and its ΔT reaches as wide as 100 K. The magnetic properties of these compounds were measured and correlated with the broadened NTE operation-temperature window. The present discovery highlights the potential applications of NTE materials in cryogenic engineering.