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Negative thermal expansion (NTE) behavior with giant thermal hysteresis exceeding 450 K has been observed in Fe3NiBx. This behavior is desirable in the field of pipe joint or encapsulation. The temperature dependent X-ray diffraction and magnetization indicate that NTE behavior with giant thermal hysteresis is related to crystal structure transition between face-centered cubic (fcc) and body-centered cubic (bcc), but not to the magnetic transition. The introduction of boron can reduce the NTE temperature range and stabilize the high temperature fcc phase. Therefore, we can obtain the NTE behavior below room temperature during cooling process, which is important for the practical application.

The antiperovskite Mn 3 Zn 0.77 Mn 0.19 N 0.94 was investigated by in situ neutron powder diffraction (NPD) in the temperature region 5–300 K. Here, a noncollinear-antiferromagnetic/collinear-ferrimagnetic phase separation (PS) showing different lattice parameters was firstly revealed in antiperovskites. The NPD results prove that the noncollinear antiferromagnetic phase, even coexisting with the collinear ferrimagnetic phase, could be responsible for the zero thermal expansion behavior of Mn 3 Zn 0.77 Mn 0.19 N 0.94 below 110 K. These findings suggest that Mn 3 ZnN based materials could open a new avenue for further exploring the noncollinear magnetic PS and correlated physical properties of antiperovskites.

An Mn3Cu0.5Ge0.5N/Cu composite was synthesized with 50 wt.% Cu and 50 wt.% Mn3Cu0.5Ge0.5N. The composite has a nearly zero thermal expansion behavior around room temperature and consists of Cu, Mn3Cu0.5Ge0.5N with a small number of MnO particles. There are no chemical reactions between these phases and the thermal expansion property of the composite is stable. Based on the distribution of Cu and Mn3Cu0.5Ge0.5N phases in the composite, we built a structure model to clarify the stability of Mn3Cu0.5Ge0.5N/Cu composite.