Thermal expansion and electrical properties of stannum doped manganese nitrides and composites

Antiperovskite manganese nitrides Mn3Cu1−xSnxN and carbon nanotubes/Mn3Cu1−xSnxN composites were prepared by mechanical ball milling and solid state sintering. The crystal structure, microscopic morphology, thermal expansion properties and electrical conductivities of Mn3Cu1−xSnxN and CNTs/Mn3Cu1−xSnxN were studied. The results show that the dominating phase of the samples has a Mn3CuN-type structure. The Mn3Cu1−xSnxN has fine and dense grains. The CNTs are distributed among the Mn3Cu1−xSnxN grains in the composites. The transition temperature of negative thermal expansion (NTE) tends to increase with increasing the content of Sn. The NTE coefficient of Mn3Cu1−xSnxN is between −27.7 × 10−6 K−1(x = 0.2) and −87.5 × 10−6 K−1 (x = 0.3). The operation temperature window is narrower and the absolute value of NTE coefficient is smaller in CNTs/Mn3Cu1−xSnxN compared to Mn3Cu1−xSnxN. The electrical conductivities of Mn3Cu1−xSnxN and CNTs/Mn3Cu1−xSnxN composites are in the ranges of 0.90–2.62 × 103 S/cm and 1.38–3.34 × 103 S/cm, respectively. The electrical conductivities decrease with increasing Sn contents for both Mn3Cu1−xSnxN and CNTs/Mn3Cu1−xSnxN.